A CATALOGUE OF N B S ATURE- ASED OLUTIONS FOR URBAN RESILIENCE Table of Contents Acknowledgments ........................5 3 The Catalogue...........................29 Foreword ...........................................7 3.1 Reader's Guide...........................30 1 Introduction ................................9 3.2 Urban NBS Families ..................38 Urban Forests ...............................42 1.1 The Urban Resilience Terraces and Slopes .....................56 Challenge ....................................9 River and Stream Renaturation...70 1.2 Nature-based Solutions .............9 Building Solutions ........................84 1.3 A Catalogue to Support Open Green Spaces ......................98 the Identification of Urban Green Corridors .........................112 NBS Investments ......................11 Urban Farming ...........................126 Bioretention Areas .....................140 2 Integrating Nature-based Natural Inland Solutions for Urban Wetlands.....................................154 Resilience ...................................15 Constructed Inland Wetlands.....................................168 2.1 Assess the Functions, River Floodplains........................182 Benefits, Suitability Mangrove Forests ......................196 © 2021 International Bank for Reconstruction and Development / The World Bank Considerations and Salt Marshes ..............................210 1818 H Street NW Costs of NBS .............................15 Washington DC 20433 Sandy Shores ..............................224 Telephone: 202-473-1000 2.2 Apply an Integrated Internet: www.worldbank.org Systems Approach to This work is a product of the staff of The World Bank and the Global Facility for Disaster Reduction and Recovery (GFDRR) with external NBS for Resilience in contributions. The findings, interpretations, and conclusions expressed in this work do not necessarily reflect the views of The World Bank, its Board of Executive Directors, or the governments they represent. Urban Landscapes .....................18 Although the World Bank and GFDRR make reasonable efforts to ensure all the information presented in this document is correct, its 2.3 Consider the Principles accuracy and integrity cannot be guaranteed. Use of any data or information from this document is at the user’s own risk and under no circumstances shall the World Bank, GFDRR or any of its partners be liable for any loss, damage, liability or expense incurred or suffered of Ecosystem Conservation which is claimed to result from reliance on the data contained in this document. The boundaries, colors, denomination, and other information shown in any map in this work do not imply any judgment on the part of The World Bank concerning the legal status of any by adopting a Hierarchy of territory or the endorsement or acceptance of such boundaries. Rights and Permissions Ecosystem-Based The material in this work is subject to copyright. Because The World Bank encourages dissemination of its knowledge, this work may be Approaches...............................20 reproduced, in whole or in part, for noncommercial purposes as long as full attribution to this work is given. 2.4 Consider the Integration Unless otherwise indicated, all original designs and drawings in this work were developed by Felixx Landscape Architects & Planners. of NBS across a Range of Any queries on rights and licenses, including subsidiary rights, should be addressed to World Bank Publications, The World Bank Group, Spatial Scales............................21 1818 H Street NW, Washington, DC 20433, USA; fax: 202-522-2625; e-mail: pubrights@worldbank.org. Suggested citation 2.5 Adopt a Multistakeholder World Bank, 2021. A Catalogue of Nature-based Solutions for Urban Resilience. Washington, D.C. World Bank Group and Interdisciplinary Approach ..................................25 Vegetated slopes and upland forests in Sarvelat, Gilan, Iran Photo by Mojtaba Hoseini on Unsplash 2 3 Acknowledgments The Catalogue of Nature-based Solutions for Urban Resilience was developed by the World Bank’s Global Program on Nature-based Solutions (GPNBS) and the City Resilience Program (CRP), under the leadership of Sameh Wahba, Global Director for Urban, Resilience and Land; Niels Holm-Nielsen, Practice Manager of the Global Facility for Disaster Reduction and Recovery (GFDRR); and Meskerem Brhane, Practice Manager for Urban, Resilience and Land, East and Southern Africa. The core team was led by Brenden Jongman, Defne Osmanoglou and Boris van Zanten, and comprised Borja González Reguero, Douglas Macfarlane, Larissa Duma, Steven Carrion and Steven Rubinyi. The Catalogue was developed in collaboration with a consortium of companies that included Felixx Landscape Architects and Planners, Nelen & Schuurmans, Rebel, UNStudio, and UNSense. The World Bank would especially like to acknowledge the contributions from Michiel Van Driessche, Eduardo Marin Salinas, Nadya Nylina, Cherk Ga Leung, Zofia Krzykawska, and Elan Redekop van der Meulen (Felixx Landscape Architects and Planners), Joost van der Hammen, Evelyn Aparicio Medrano, and Thomas van Veelen (Nelen & Schuurmans), Benan Berhan and Johan Gauderis (Rebel Group), Ren Yee (UNSense) and Dana Behrman (UNStudio). The Catalogue further built extensively on collaborative input from many reviewers to progress through the iterations of its textual content and we express our sincere gratitude to the following people who provided incisive comments and guidance on this report: Ana Campos García, Annu Rajbhandari, Andrey Shanin, Eric Dickson, Gonzalo Goizueta, Irene Rehberger Bescos, Joop Stoutjesdijk, Juan Jose Miranda, Juliana Castaño Isaza, Kavita Kapur Macleod, Klaas de Groot, Laurent Corroyer, Marcus Wishart, Maria Catalina Ramirez, Nicholas Jones, Rob Pilkington, Ross Eisenberg, William Ouellette, Xueman Wang. Chitra Arcot edited the Catalogue. This report was prepared with support from the World Bank’s Global Facility for Disaster Reduction and Recovery (GFDRR). in collaboration with: A dense tree canopy in Hanoi, Vietnam Photo by Raissa Lara Lütolf on Unsplash 4 Foreword More than half of the world's population lives in cities, and that number is rising every day. Urban areas are becoming more crowded, corrosively reducing green spaces within cities, and causing loss of biodiversity, and in turn, affecting people’s mental and physical well-being and exposure to disaster impacts. At the same time, cities are facing growing climate-related challenges. Climate change and urbanization are exacerbating disaster risks, and these risks are affecting the poor and the vulnerable the most. By protecting natural systems and investing in green infrastructure, cities have the opportunity to build resilience and protect development gains for future generations. Globally, the interest in nature-based solutions (NBS) or using nature for climate resilience, is growing. Key international agreements, such as the Sendai Framework for Disaster Risk Reduction, the Paris Climate Agreement, and Sustainable Development Goals, underline the importance of NBS as dependable approaches that address climate change. Nature- based solutions also contribute to people’s well-being and support biodiversity, as well as remove carbon dioxide from the atmosphere as noted in the Sixth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), which provides an additional rationale for investment. The World Bank has a growing portfolio of NBS investments for disaster risk management and climate resilience, which amounted to nearly US$5 billion between 2012 and 2020. In Beira, Mozambique, a 17-hectare, multifunctional urban green park along the Chiveve River was financed by the World Bank to provide various recreational and economic opportunities for residents, while also restoring the river’s natural ability to retain water and mitigate floods. In Freetown, Sierra Leone, a community-based reforestation project—to combat deforestation and its accompanying loss of biodiversity, and counter the severity of natural hazards—has created more than 550 jobs to support local economies impacted by the COVID-19 pandemic. Despite the growing demand for NBS in cities, many people who make planning, financing, and technical decisions for urban resilience building have little knowledge of when and how to build with nature. It creates a need for better guidance, more real-world examples that illustrate how such approaches have worked, and technical assistance to help support more cities identify potentially viable nature-based investments that help cities address resilience challenges. Thus, this Catalogue of Nature-based Solutions for Urban Resilience was created as a resource for those aiming to shape urban resilience with nature. The Catalogue was jointly launched by the Global Program on Nature-Based Solutions for Climate Resilience and the City Resilience Program, both housed in the Global Facility for Disaster Reduction and Recovery (GFDRR). Developed with a specialized cohort from Felixx Landscape Architects and Planners, Nelen & Schuurmans, Rebel, UNStudio, and UNSense, and a team of experts from the Word Bank, the Catalogue provides good practice examples, design, benefits, and implementation considerations. It gives insight to the suitability of NBS in the urban landscape and their effectiveness for climate resilience. We hope that this Catalogue will support the identification of potential investments, start policy dialogues on NBS in cities, and inspire any person—policy maker, project developer, development professional, urban planner, engineer, or ecologist—to work with nature to address urban resilience challenges. Niels Holm-Nielsen Practice Manager GFDRR World Bank A meandering river with a dense riparian forest in Ivanovo Oblast, Russia Photo by Alexandr Bormotin on Unsplash 6 7 Chapter 01 Introduction 1.1 The Urban Resilience Challenge Cities worldwide are facing resilience challenges as climate risks interact with urbanization, loss of biodiversity and ecosystem services, poverty, and rising socioeconomic inequality. Extreme precipitation events, flooding, heatwaves, and droughts are causing economic losses, social insecurity, and affecting wellbeing. Over time, urban resilience challenges are expected to grow, driven by processes such as urbanization, land use, and climate change. Whereas climate change is expected to increase the frequency and intensity of some natural hazards, urbanization can also lead to higher exposure of people and assets in cities. More than half of the global population lives in cities, and more than 70 percent are expected to do so by 2050 (Wijesiri et al. 2020; Nerini et al. 2018). In rapidly urbanizing areas, a significant proportion of urban growth risks to materialize in dense, lower-quality unplanned settlements. In these vulnerable areas, climate impacts are exacerbated—now and into the future—as these settlements are often located in high-risk areas, such as on floodplains or steep slopes (Hallegatte et al. 2017). In addition, poorly maintained infrastructure, such as drainage systems, and impervious surfaces can increase the magnitude of natural hazards, such as flooding and urban heat island effects. The World Bank has a growing portfolio of investments and analytical engagements in urban resilience. In the past, structural interventions to reduce disaster risk and build climate resilience have largely focused on gray infrastructure. However, gray infrastructure will not always be suitable in cost-effectiveness, resiliency, or sustainability. More than ever, nature-based solutions (NBS) are recognized to have a critical role in addressing resilience challenges urban areas (box 1-1). The need to advance nature-based approaches is endorsed by many international agreements and initiatives such as the Sendai Framework for Disaster Risk Reduction, the Sustainable Development Goals (SDGs), and the Paris Climate Agreement. These agreements support an alignment of environmental and risk management goals to address the burgeoning needs of managing climate risk, to confront environmental degradation, to improve the adaptive capacities of vulnerable communities, and to advance public and private investment in disaster risk prevention and reduction (Reguero et al. 2020). Box 1-1: Definitions 1. Gray infrastructure refers to built structures and mechanical equipment, such as reservoirs, embankments, pipes, pumps, water treatment plants, and canals. These engineered solutions are embedded within watersheds or coastal ecosystems whose hydrological and environmental attributes profoundly affect the performance of the gray infrastructure. (World Bank and World Resources Institute. 2019.) 2. Nature-based solutions (NBS) is an umbrella term referring to “actions to protect, sustainably manage, and restore natural or modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits.” (Cohen-Shacham et al. 2016.) A green corridor runs parallel to railway infrastructure in Hanoi, Vietnam Photo by Hoach Le Dinh on Unsplash 8 9 1.2 Nature-based Solutions 1.3 A Catalogue to Support the Identification of Urban NBS Investments Nature-based solutions are approaches that use nature and natural processes for delivering infrastructure, services, and The Catalogue of Nature-based Solutions for Urban Resilience has been developed as a guidance document to support integrative solutions to meet the rising challenge of urban resilience. These interventions usually go beyond sectoral the growing demand for NBS by enabling an initial identification of potential investments in nature-based solutions. boundaries and require cross-sectoral partnership. NBS can provide multiple benefits to cities and address different Consolidating insights of the performance and benefits of the 14 NBS typologies—hereafter “NBS families”—presented societal challenges, including reducing disaster risk and building climate resilience, while also contributing to restore in figure 1-1, intends to support policy makers, project developers, development professionals, urban planners, and biodiversity, creating opportunities for recreation, improving human health, water and food security, and supporting engineers with the identification of potential NBS investments, and to start a policy dialogue on NBS in cities. community wellbeing and livelihoods. Two key questions in the initial scoping of nature-based solutions potential are: (i) What are the desired benefits from NBS use a set of structural and non-structural interventions that protect, manage, restore, or create natural or nature- the NBS? and (ii) Is the NBS suitable at the location? To help answer these two questions, the Catalogue provides: (i) based features. Alongside other benefits, NBS can reduce the impact of natural hazards in cities, such as flooding, erosion, technical descriptions, visualizations, and examples to better assess the potential of NBS in urban areas; (ii) unit costs landslides, drought, and extreme heat (Ozment et al. 2019; Sudmeier-Rieux et al. 2021). They can also complement gray and benefits’ estimates to help assess the economic viability; and (iii) suitability considerations to provide guidance on infrastructure such as storm drains, embankments, and retaining walls. In many cases, integration of NBS has proven to possible locations for NBS (see also figure 2-1). The Catalogue focuses mainly on nature-based solutions for flood and be cost-effective (Raymond et al. 2017). heat risk management in urban areas, but it also provides insights for other social and environmental benefits of NBS. Nature-based solutions for urban resilience can be applied across spatial scales and settings in and around cities. This Catalogue complements and builds on other knowledge products on NBS developed by the World Bank (Jongman Examples include small scale green spaces on buildings, bioswales, and green corridors along streets and water bodies, and Ozment 2019; World Bank 2017; Browder et al. 2019) to support the integration of NBS in investment projects. The urban parks and forests within city boundaries, and larger areas with wetlands and forests upstream or along the coast, document represents a selection of prevailing thinking around urban NBS in a quickly evolving and growing field. sheltering cities from flooding and improving availability and quality of water. Figure 1-1 includes an overview of common NBS typologies. The document is structured as follows: Chapter 2 describes generic principles for integrating NBS into urban environments. Chapter 3 provides a reader’s guide and holds the Catalogue of the 14 NBS families that include: Urban Forests, Terraces A momentum is growing for NBS as a vehicle for delivering green resilient and inclusive development, especially in the and Slopes, River and Stream Renaturation, Building Solutions, Open Green Spaces, Green Corridors, Urban Farming, context of economic recovery from the COVID-19 pandemic. Demand and interest from World Bank clients in investing in Bioretention Areas, Natural Inland Wetlands, Constructed Inland Wetlands, River Floodplains, Mangrove Forests, Salt NBS is steadily rising. Since 2012, the World Bank’s portfolio of NBS investment projects contributing to climate resilience Marshes, and Sandy Shores. is worth nearly 5 billion USD. NBS investments have increased especially sharply in the last three years, 2018–2020, when the total number of NBS-lending projects rose by 35 percent. Figure 1-1: Diversity of nature-based solutions for urban application River and Stream Open Green Urban Forests Terraces and Slopes Renaturation Building Solutions Spaces Green Corridors Urban Farming Natural Constructed Bioretention Areas Inland Wetlands Inland Wetlands River Floodplains Mangrove Forests Salt Marshes Sandy Shores 10 11 REFERENCES Browder, G., Ozment, S., Rehberger Bescos, I., Gartner, T., and Lange, G-M. 2019. Integrating Green and Gray : Creating Next Generation Infrastructure. Washington, D.C.: World Bank and World Resources Institute. https:// openknowledge.worldbank.org/handle/10986/31430 Cohen-Shacham, E., Walters, G., C. Janzen, and Maginnis, S. 2016. Editors: Nature-based Solutions to address global societal challenges. International Union for Conservation of Nature (IUCN). Gland, Switzerland. https://portals.iucn. org/library/sites/library/files/documents/2016-036.pdf Hallegatte, S., Vogt-Schilb, A., Bangalore, M., and Rozenberg, J. 2017. Unbreakable : Building the Resilience of the Poor in the Face of Natural Disasters. Climate Change and Development. Washington, D.C. World Bank. https:// openknowledge.worldbank.org/handle/10986/25335 Jongman, B., and Ozment, S. 2019. What if we could use nature to prevent disasters? World Bank. https://blogs. worldbank.org/sustainablecities/what-if-we-could-use-nature-prevent-disasters Nerini, F.F., Tomei, J., To, L.S., Bisaga, I., Parikh, P., Black, M., Borrion, A., Spataru, C., Broto, V.C., Anandarajah, G. and Milligan, B. 2018. Mapping synergies and trade-offs between energy and the Sustainable Development Goals. Nature Energy, 3(1), 10–15. Ozment, S., Ellison, G., and Jongman, B. 2019. Nature-Based Solutions for Disaster Risk Management. Washington, D.C. World Bank Group. https://documents1.worldbank.org/curated/en/253401551126252092/pdf/134847-NBS-for- DRM-booklet.pdf Raymond, C.M., Frantzeskaki, N., Kabisch, N., Berry, P., Breil, M., Nita, M.R., David Geneletti, D., and Calfapietra, C. 2017. A framework for assessing and implementing the co-benefits of nature-based solutions in urban areas. Environmental Science & Policy, 77:15–24. https://www.sciencedirect.com/science/article/pii/S1462901117306317#! Reguero, B.G., Beck, M.W., Schmid, D., Stadtmüller, D., Raepple, J., Schüssele, S., and Pfliegner, K. 2020. Financing coastal resilience by combining nature-based risk reduction with insurance. Ecological Economics; 169. https://doi. org/10.1016/j.ecolecon.2019.106487 Sudmeier-Rieux, K., Arce-Mojica, T., Boehmer, H.J., Doswald, N., Emerton, L., Friess, D.A., Galvin, S., Hagenlocher, M., James, H., Laban, P., Lacambra, C., Lange, W., McAdoo, B.G., Moos, C., Mysiak, J., Narvaez, L., Nehren, U., Peduzzi, P., Renaud, F.G., Sandholz, S., Schreyers, L., Sebesvari, Z., Tom, T., Triyanti, A., van Eijk, P., van Staveren, M., Vicarelli, M. & Walz, Y. 2021. Scientific evidence for ecosystem-based disaster risk reduction. Nature Sustainability. https://doi. org/10.1038/s41893-021-00732-4 Wijesiri, B., Liu, A., and Goonetilleke, A. 2020. Impact of global warming on urban stormwater quality: From the perspective of an alternative water resource. Journal of Cleaner Production, 262, 121330. World Bank. 2017. Implementing nature-based flood protection. https://documents1.worldbank.org/curated/ en/739421509427698706/pdf/Implementing-nature-based-flood-protection-principles-and-implementation- guidance.pdf A lush green structure integrated into a residential area Photo by Vista Wei on Unsplash 12 13 Chapter 02 Integrating Nature-based Solutions for Urban Resilience The urban landscape is an interconnected system. The built environment functions as a system that modifies the local hydrology and climate, and hence, influences the frequency and intensity of hydrometeorological natural hazards. At the same time, the built environment can often hinder large-scale NBS because of space constraints. Critical considerations can be defined that enable the integration of NBS in the urban landscape. One enlightened approach, for example, would be that project developers and planners follow an approach of "green where possible, gray when needed". This chapter describes five important principles for the integration of NBS in cities—that hold good for all NBS families in the Catalogue—and that can guide the identification and realization of potential investments in NBS: 1. Assess the functions, benefits, costs, and suitability considerations of NBS 2. Apply an integrated systems approach to NBS for resilience in urban landscapes 3. Consider the principles of ecosystem conservation by adopting a hierarchy of ecosystem-based approaches 4. Consider the integration of NBS across a range of spatial scales 5. Adopt a multistakeholder and interdisciplinary approach 2.1. Assess the Functions, Benefits, Suitability Considerations and Costs of NBS Assessments on functions, benefits, location suitability, and costs of NBS enable an initial identification of locations of potential investments. It increases understanding of the socioeconomic values of NBS and helps identify locations where environmental, technical, or urban conditions are suitable for NBS (figure 2-1). In the Catalogue, this information is provided for every NBS family. Functions, benefits, and suitability considerations Each NBS is characterized by a set of processes that defines their functions and the benefits they provide. Processes of NBS may involve stormwater infiltration and evapotranspiration. ‘Functions’ refer to the capacity of NBS to provide benefits to people. For example, NBS can regulate flooding or reduce extreme heat, stabilize soils, or improve water quality. These functions are an important intermediate step for understanding the value, or benefits, of NBS for people. ‘Benefits’ are provided if there are people who directly or indirectly benefit from NBS functions. This, for example, includes reduced flood damages, reduced heat stress, or the use of green space for recreation. In comparison to gray infrastructure, NBS provide a variety of benefits to society such as flood risk reduction, heat stress reduction, human health, recreation, tourism, and biodiversity. Often, the full suite of benefits that NBS offer represents an important factor in decision making. In the Catalogue, each NBS family includes a visualization of their processes, a section describing its functions, and a section with its benefits described qualitatively (box 2-1). An urban park in Nairobi, Kenya Photo by Zac Wolff on Unsplash 14 15 Considerations on locations of NBS can help in understanding whether an NBS could be suitable at a location in or around Costs a city, which may, for example, depend on the local climate, terrain, available space, or maintenance needs. These location suitability considerations are subdivided in the Catalogue in environmental, technical and urban categories. For each NBS type, the Catalogue outlines key cost considerations for the investment and implementation stage, such as land-related costs, NBS construction costs, or longer-term maintenance costs. In addition, examples of unit costs are provided. However, such unit cost estimates should only be taken as indicative, as NBS costs may vary significantly across locations (box 2-2). Factors that influence costs include, for example, the approach taken by the project—protection, Figure 2-1: A framework to support the first identification of potential investments in NBS rehabilitation/restoration, or creation—and numerous other economic, environmental, and project-level labor and material costs. • Upfront costs Processes - Infiltration - Evapotranspiration Upfront costs of NBS include costs associated with securing the land upon which the NBS will be installed and costs - Water storage Functions for planning, installing, and overseeing the effective implementation of NBS measures. - Aquifer recharge - Flood regulation - Heat regulation Benefits for people Land-related costs of implementing NBS are dependent on: the extent of land the extent of land area required - Soil stabilization - Reduced flood risk - Water retention for the NBS, which is sometimes large; whether land must be purchased to implement the NBS; and, if land must - Reduced heat stress be purchased or otherwise obtained for use; whether the land is held publicly or privately; and the relative value - Outdoor recreation - Human health of the land. Land values are driven by the opportunity cost of using the land for NBS versus other purposes— Is the NBS - Biodiversity agricultural cultivation; residential or commercial development; open space or recreation—and beneficial uses suitable at to which the land could be put. Land-related costs in a Developing Country context are in part generated by this location? necessary engagement and collaboration with multiple stakeholders to secure land acquisition or use, and must consider social safeguards and social inclusion of local communities, especially regarding indigenous peoples and women. Identify NBS and approach to protect, enhance, restore, What are NBS installation or implementation costs are driven by labor and materials needed for the project. The type and create natural or modified ecosystems. the desired of NBS and site-specific factors such as local materials, topography, preparatory works required, hydrological benefits of conditions, transportation, or access to the correct types of trees and plants to be used. the NBS? • Maintenance costs Maintenance costs are the actions required to maintain a functional NBS, providing the benefits it was designed for. Maintenance costs include routine monitoring or inspection to determine necessary maintenance actions, Note: The information per NBS family is organized to provide an understanding of the and implementation of these maintenance activities on a regular basis. NBS maintenance activities may include processes, functions, benefits, and location suitability of NBS. The lists in the boxes are enforcing area protection avoiding encroachment, removal and disposal of debris and dead plant material; examples and not intended to be exhaustive. weeding; pruning or thinning; removal of invasive species; replanting; and fertilizing. Effective maintenance actions are critical to NBS project sustainability and success and require upfront planning and long-term funding to realize. Box 2-1: Benefits assessment is important for identifying project financing Box 2-2: Key cost-related caveats After the scoping phase and identification of NBS (and beyond the scope of this Catalogue), a thorough Actual project-level NBS costs may differ from the example unit cost estimates provided in the Catalogue for the assessment of the benefits and beneficiaries of NBS is critical for the identification of financing options. The following reasons: principal sources of funding are based on sustainable revenues derived from tariffs, taxes, or transfers that determine how investment costs are repaid over time, while also supporting project life cycle costs. Governments NBS project costs vary significantly and are highly site- and project-specific. Unit costs will also vary over time have traditionally played a key role in providing economic and social infrastructure, both as financier and by with changing land, labor, and materials prices. In addition, economies of scale may be present with larger projects, leading some unit cost estimates to overestimate potential projectwide costs. establishing the enabling policies and regulations. However, public investments alone are often not sufficient, given the size of investment required to meet future challenges relating to building urban resilience. Valuation Many unit cost estimates in the literature are derived from developed countries, where unit costs may be much of a broad range of benefits can provide opportunities to leverage a wider array of financing options that can higher than in the developing country context due to higher labor and materials costs and other location- help promote the application of nature-based solutions and continuous improvements in the quality of life and specific costs. For example, one source lists the costs of dredging as US$2/ m3 in Bangladesh and US$59/m3 in urban landscape. Based on the potential benefits and beneficiaries identified, different financing mechanisms and sources can be adopted and leveraged (Wishart et. al. 2021). 16 17 understanding of the local ecology including temperature, rainfall, soils, and the selection of naturally occurring plant species for their use in NBS projects. the UK (Aerts 2018). Costs from the developed world may be therefore limited in their ability to represent actual costs in developing countries. While resilience and biodiversity benefits are key in NBS design, it is often the variety of co-benefits contributing to human wellbeing that supports the value proposition over gray infrastructure alternatives. These include aesthetic Unit cost estimates associated with implementing NBS in rural areas may be lower than in urban areas given the benefits that make neighborhoods more attractive to urban residents and cultural benefits including opportunities for higher transaction costs that typically accompany urban projects (for example, municipal zoning and permit or relaxation and recreation. The longevity of NBS also requires the support of local communities and as such, warrants a construction requirements; larger numbers and greater density of landowners and fragmented landownership; need to integrate local community needs and aspirations into planning to ensure that interventions are supported and larger number of stakeholders requiring engagement) and frequently higher costs of labor and materials in maintained in the long term. urban areas. Unit cost estimates in the literature vary depending on the components the project included—for example, land acquisition, construction technique, types of materials, maintenance needed—. Some estimates bundle multiple components together, which makes difficult to isolate and compare upfront costs from other longer- term sources of project cost. Figure 2-2: Example of a hybrid solution integrating green and gray infrastructure 2.2. Apply an Integrated Systems Approach to NBS for Resilience in Urban Landscapes Evapotranspiration Carbon Water storage Nature-based solutions aimed to increase urban resilience are often most effective when approached and planned sequestration and reuse in an integrated or holistic manner, especially in complex urban environments. This means first taking a system-based approach to address resilience and biodiversity challenges, and then, seeking practical ways to integrate NBS into policies plans, programs, and projects. Cooling effect Taking an integrated systems approach also means that NBS should not be designed independently, but rather to complement and strengthen existing risk management interventions. NBS can, for example, augment and complement existing gray infrastructure, gradually increasing the overall capacity of the system, and its efficacy and efficiency on risk reduction and co-benefits to the urban landscape. Such integration is not only necessary at a system level, but should also be considered at a local scale where hybrid solutions—a combination of nature-based features and gray Shade infrastructure elements—may provide the most efficient solution (figure 2-2). Water collection Consequently, NBS can be integrated into broader programs, such as risk management plans, plans for designs of structural measures, proactive urban and land use planning, evacuation management, and sustainable maintenance. As most NBS are multifunctional, they can perform a variety of functions at different scales, and respond to several resilience demands, such as managing flooding and extreme heat effects, at different times. For example, the same NBS implemented as part of a larger systems approach can retain, filter, and convey water protecting cities from floods as well as droughts. A hilly area with loose soils, debilitated from water damage and erosion, can benefit from an appropriately designed slope stabilizing NBS, while at the same time retaining runoff and conveying water down to the areas where it is needed (Jha et al. 2012). Infiltration Soil cleaning With the alarming levels of biodiversity loss, cities also have a responsibility to contribute to global efforts to restore, strengthen, and enhance biodiversity. In practice, this involves ensuring that critical biodiversity areas are protected and effectively managed, and that ecological networks are enhanced to promote the movement of wildlife that is necessary for dispersing, foraging, and maintaining genetic diversity. Planning of ecological networks is therefore critical in cities where NBS can be used to provide supplementary habitat. Optimizing these benefits does, however, require an Building Reflective Underground Rain sewer Bioretention Green Permeable solutions materials water areas corridors pavements storage 18 19 2.3 Consider the Principles of Ecosystem Conservation by adopting a Hierarchy of enhanced through carefully planned rehabilitation and restoration initiatives. In coastal regions, the benefits provided by mangroves, salt marshes, and sandy shores can also be strengthened through restoration efforts. Co-benefits of Ecosystem-based Approaches productive lands can also be enhanced through terracing and appropriate slope stabilization measures, and the implementation of sustainable urban farming methods. Opportunities also exist to enhance and strengthen a broad Nature-based solutions are an umbrella concept covering a range of ecosystem-based approaches including protection, suite of benefits provided by existing urban green spaces and green corridors through enhanced design, landscaping, sustainable management, restoration, and creation of natural or green infrastructure (Cohen-Shacham et al. 2019). and replanting measures. The third layer, creation of new NBS, can be used to mitigate impacts and strengthen urban These approaches can be considered in a hierarchy, prioritizing the protection of existing ecosystems over enhanced resilience. This includes new natural or green infrastructure interventions such as green roofs, vegetated facades, management, rehabilitation and restoration, or the creation of new NBS (figure 2-3). At the same time the three constructed wetlands, and bioretention areas. These new NBS can also provide other co-benefits to communities. elements—protection, restoration, and creation of new NBS—are complementary and the development of an NBS strategy should assess all elements. Consideration of this hierarchy is particularly relevant when investigating and prioritizing NBS opportunities at a strategic level, such as when screening investment opportunities for a city. However, the three approaches can also be adopted for planning and preparing NBS projects at the neighborhood, city, and river 2.4 Consider the Integration of NBS across a Range of Spatial Scales basin scales (see also section 2.4). The Catalogue indicates which of the ecosystem-based approaches can be applied for NBS should be considered at a range of spatial scales. The Catalogue considers NBS at three spatial scales: the river each NBS family. basin scale, the city scale, and the neighborhood scale. The different scales at which the NBS can be implemented are indicated for every NBS family. For example, floodplain restoration that re-establishes natural hydraulic and Adopting the hierarchy of these three elements supports the need to take a strategic approach to planning. It also hydrological connectivity can help manage flood hazards at the river basin scale, whereas bioswales can be planned at emphasizes the importance of evaluating opportunities to strengthen the protection of existing natural infrastructure the neighborhood level. in a city to maintain functional and biodiversity values. Natural wetlands, grasslands, floodplains, urban forests, and mangroves are all examples of ecosystems in and around urban areas that can be protected to secure existing benefits. This section describes the difference between these spatial scales for flood resilience problems. Urban areas can be This requires their formal integration into zoning schemes and the application of measures to prevent encroachment affected by riverine flooding, coastal flooding, and either pluvial or ground water floods or combinations. These floods and degradation. can be the result of a complex combination of causes, such as meteorological and hydrological extremes, including extreme precipitation, river discharges and storm surges, and failure of flood defenses. NBS can serve to mitigate and While protection is critical, untransformed land in urban areas is typically exposed to a broad suite of impacts that can adapt to flood risk. They can contribute to flood risk reduction by controlling the flow of water both outside and within adversely affect the capacity to deliver valuable ecosystem services. The second layer focuses on the restoration and urban settlements. Offshore or upstream measures at some distance from the affected city that reduce storm surges rehabilitation of ecosystems to enhance their performance, functioning, and benefits. Deforestation, for example, can or slow down runoff can tackle flooding problems before floods reach the urban areas. For example, in the event of a be addressed through active reforestation, while the benefits provided by streams, wetlands, and floodplains can be heavy storm, inland NBS such as forests can hold water upstream, relieving the pressure from the downstream part of the system and thereby protecting the river. At the same time, adaptation measures within the city can be applied to prepare the built environment in towns and cities with their concentrated population centers, buildings and urban Figure 2-3: A hierarchy of approaches under the nature-based solutions umbrella infrastructure, and strengthen their resilience (Jha et al. 2012). The river basin scale PROTECTION AND SUSTAINABLE MANAGEMENT OF Cities can be located at different positions in a river basin—at the most upstream location in the mountains to the downstream region at the coast. To some degree, their position determines the suitability of NBS types in the city at EXISTING NBS TO SUSTAIN BENEFITS AND hand. Cities can be classified by their position in the river basin, along with their main characteristics into (see also figure BIODIVERSITY 2-4): • Mountainous cities, located at higher elevations, often with steep slopes, are characterized by an extensive ENHANCEMENT network of streams, and are vulnerable to flash floods from stormwater, erosion, and landslides. RESTORATION AND REHABILITATION OF • River cities, located along the large river systems, benefit from fertile soils and access to river trading, but also DEGRADED NBS experience seasonal water-level fluctuations, and are often susceptible to flooding. REGENERATING BENEFITS • Delta cities are often flood-prone regions and highly influenced by hydrological dynamics, including dynamics CREATION between fresh and brackish water and sedimentation. They are also home to highly productive and nutrient- rich wetland ecosystems and soils. OF NEW NBS • Coastal cities are located along shorelines and benefit from coastal ecosystem services. At the same time, these cities are exposed to the impact of sea level rise, coastal flooding, erosion, and also other threats such as subsidence or saltwater intrusion. 20 21 Figure 2-4: Different types of cities based on their location in the river basin. Suitable NBS can be considered NBS at the river basin scale recognize the interconnectedness of communities and the importance of integrated dependent on the characteristics of the city such as the hydrological conditions. catchment management approaches to address flooding and water resource challenges. These include NBS that address the problem near the source, outside of the city, and aim to tackle the problem before it reaches the city. Examples of NBS that benefit cities but which take a broader river basin scale perspective (figure 2-5) include: • Restoration of forest cover in upland areas to intercept and slow floodwater. • Rehabilitation of river floodplains to enhance storage and reduce flood risks in downstream areas. • Restoration of mangrove forests outside the city to decrease wave energy and storm surges. Mountainous cities Figure 2-5: Schematic section of NBS at the river basin scale River cities Artificial Mangrove Sandy Natural River Upland reefs forests shores inland floodplains forests wetlands The city scale NBS at the city scale include measures in a city or town that seek to complement and strengthen urban land use planning and to support disaster risk management. The landscape and ecological structure of the city, together with the unique challenges faced by city residents, determine the suitability and potential of NBS. A broad suite of characteristics can be distinguished that affect the applicability of NBS such as the terrain, climate, hydrology, ecology, and sociology. Some Delta cities examples of NBS that are typically considered at city level are (figure 2-6): • Urban forests and terracing on higher elevation levels to delay runoff. • Creation of constructed wetlands or wetland restoration in lower urban areas to collect and store water runoff. • Renaturation of existing streams and drainage lines in the city to slow down water flows. • Increase of open green spaces or parks throughout the city to add infiltration capacity and reduce urban heat. Coastal cities • Continuity of linear tree canopies and green corridors along roads in the city to reduce urban heat and strengthen biodiversity networks. 22 23 Figure 2-6: Schematic section of NBS at the city scale Figure 2-7: Schematic section of NBS at the neighborhood scale NBS at the building scale River Natural Open green Constructed Green River and Terraces Urban Green Green Retention Pocket River and Bioretention Urban floodplains inland spaces inland corridors stream and forests walls roofs ponds parks stream areas farming wetlands wetlands renaturation slopes renaturation The neighborhood scale Box 2-3: Spatial considerations for arid and semi-arid urban contexts At the neighborhood scale, resilience challenges are addressed at a local level including measures in buildings, streets, and open public spaces (figure 2-7). These often smaller-scale interventions can build resilience by increasing stormwater Planning and implementing NBS in arid and semi-arid urban contexts requires several special considerations. retention capacities and reducing the heat island effect, for example. These NBS can be very effective for local rainwater Arid and semi-arid landscapes, as well as landscapes with distinct wet and dry seasons, can be particularly collection, to mitigate impacts of air, water, and soil contamination, and to reduce heat levels in cities by providing shade. challenging environments for plants and trees to thrive which are critical components for several of the NBS. Neighborhoods can be established as functional clusters of resilience. Implementing NBS at the neighborhood level can NBS planning for these contexts should integrate detailed analysis of the environmental factors critical for relieve pressure on existing local infrastructure such as stormwater drains. At the neighborhood level, collaboration plant and tree survival including sunlight intensity and directness, rainfall patterns, surface water flows, and between the public and the private domain is key, and NBS implementation can help build alliances between the groundwater levels and access. The planning phase should also include a detailed assessment of indigenous different stakeholders—governments, private sector, property owners, and communities—. Examples of NBS at the plant and tree species inclusive of their ideal growing conditions such as their tolerances to direct sun and neighborhood scale include: water requirements, which should be incorporated into the implementation and maintenance plans. Sufficient resources should be allocated including financing for watering and general maintenance for prolonged periods post-implementation to ensure the survival and establishment of all plants and trees for the NBS. •NBS integrated into buildings such as green roofs, green facades, private gardens in combination with green streets. Such measures can both regulate temperature and store water. • Retention basins, rainwater retention ponds, or green water squares to store water. 2.5 Adopt a Multistakeholder and Interdisciplinary Approach • Small-scale rainwater catchment and drainage interventions such as bioswales. Integrating NBS into urban resilience strategies requires a collaborative, interdisciplinary, and cross-sectoral approach. This means extensive coordination through project phases—starting from the identification and design to the implementation and operation —and between a variety of actors, including city governments, national governments, ministries, public sector companies, meteorological and planning institutions, civil society, non-government organizations, educational institutions and research centers, and the private sector (Frantzeskaki 2019). Successful realization of NBS requires interactive development of holistic long-term strategies that balance existing resilience needs with sustainable development (Jha et al. 2012). It also involves an interdisciplinary approach that 24 25 integrates flood risk management, land use planning, and climate change adaptation strategies. Interdisciplinary teams of urban planners, landscape architects, urbanists, civil engineers, and stakeholders should actively collaborate in the planning and design process of urban resilience projects to provide more comprehensive solutions to urban challenges (box 2-3). This is particularly relevant in urban environments that typically have significant space constraints and that have led to an increase in societal emphasis on the spatial and environmental footprint and impact of interventions in urbanizing areas (Nillesen 2018). Given their interdisciplinary and cross-sectoral character, NBS projects have the unique capacity and opportunity to catalyze better cross-sectoral collaboration. This could support a shift from fragmented, siloed planning of urban interventions toward a systems-planning approach to achieve urban resilience objectives while using the available resources in an efficient manner. REFERENCES Cohen-Shacham, E., Andrade, A., Dalton, J., Dudley, N., Jones, M., Kumar, C., Maginnis, S., Maynard, S., Nelson, C.R., Renaud, F.G. and Welling, R. 2019. Core principles for successfully implementing and upscaling Nature-based Solutions. Environmental Science & Policy, 98:20–29. https://www.iucn.org/sites/ dev/files/content/documents/core_principles_for_successfully_implementing_and_upscaling_nature- basedsolutions.pdf Frantzeskaki, N. 2019. Seven lessons for planning nature-based solutions in cities. Environmental Science & policy, 93:101–111. https://www.sciencedirect.com/science/article/pii/ S1462901118310888 Jha, A.K., Bloch, R. and Lamond, J. 2012. Cities and flooding: a guide to integrated urban flood risk management for the 21st century. The World Bank. https://openknowledge.worldbank.org/ handle/10986/2241 Nillesen, A.L. 2018. Delft University of Technology, Faculty of Architecture and the Built Environment, Department of Urbanism. Spatial Quality as a decisive criterion in flood risk strategies. https://journals. open.tudelft.nl/abe/article/view/3247/3430 Wishart, M.; Wong, T., Furmage, B., Liao, X., Pannell, D., and Wang, J. 2021. Valuing the Benefits of Nature- Based Solutions : A Manual for Integrated Urban Flood Management in China. World Bank, Washington, DC. © World Bank. https://openknowledge.worldbank.org/handle/10986/35710 License: CC BY 3.0 IGO. Lush courtyard in Spain Photo by Alevision.co on Unsplash 26 27 Chapter 03 THE CATALOGUE A pocket park in India Photo by Chander Mohan on Unsplash 28 29 3.1 Reader’s Guide Processes Figure 3-2: Processes icons The Catalogue consists of 14 chapters, one for each NBS family. This chapter guides the reader through the different The technical profile of NBS illustrates processes that sections by explaining the nature of information included in every section. This can help the reader take the first step to are relevant for its resilience functions and benefits assess possible locations for NBS. Each NBS family chapter consists of following sections: (figure 3-1). Water collection Aquifer recharge 1. Facts and figures The left panel (figure 3-1) represents a sample technical 2. Visualizations profile that is provided for each NBS family. It indicates Buffer capacity Shade the characteristic processes of NBS that are considered 3. Functions in this Catalogue, which are individually outlined in the 4. Benefits right panel (figure 3-2). Wave and surge reduction Permeability 5. Suitability considerations 6. Costs 7. NBS in practice Figure 3-1: Technical profile NBS processes Cooling effect Water delay Evapotranspiration Water reuse FACTS AND FIGURES Fresh water Infiltration balance Short descriptions Sediment Generic background information about the NBS family. Water storage trapping and stabilization Type of city Cleaning capacity Overflow Information about the type of city the NBS can be applied to, with respect to the position of the city into the river basin, including mountainous, river, delta and Carbon coastal cities (see also figure 2-4). Coastal Delta River Mountain Sequestration Biodiversity Scale The spatial scale at which the NBS can be applied, including the river basin, city, and neighborhood scale. VISUALIZATIONS River basin City Neighborhood This section includes visualizations and landscaping sketches, developed for each NBS family in a uniform style to Approach illustrate certain NBS designs in the urban landscape, including technical and spatial characteristics and environmental How the planning of NBS can be approached through qualities. The visualizations also provide insight to how NBS can be seen from a systems perspective and how they ecosystem-based approaches: are most effective when integrated at different scales. This section includes following visualizations: (i) visualization of 1. Protection of existing ecosystems or NBS; the NBS in the urban context; (ii) details of increased benefits for the urban living environment; and (iii) special NBS 2. Rehabilitation of degraded ecosystems or NBS; techniques within the family. 3. Creation of new NBS. Protect Rehabilitate, Create restore, and enhance 30 31 FUNCTIONS Visualization of the NBS in the urban context This section describes the functions of each NBS family. Figure 3-4: Functions icons Functions refer to the capacity of NBS to provide A bird’s eye view of the NBS illustrating the urban benefits to people. These functions may describe context and the connection with the built environment, the regulation of potential natural hazards, such as typical topographical profiles and settings, and a flooding, extreme heat, drought or erosion. They Pluvial flood Subsidence representative spatial scale of the NBS in an urban can also describe the functions underpinning other regulation regulation area. regulating ecosystems services, such as mitigating pollution, preventing land subsidence or improving water quality. Riverine flood regulation Biodiversity A chart visualizes the relative importance of NBS functions. The flood and heat regulating functions are Coastal flood Coastal erosion described for each NBS family, while the remaining regulation regulation functions are summarized under other functions. The left panel (figure 3-3) represents a sample diagram that is provided for each NBS family. The icons that were Heat Salt intrusion included in this Catalogue are individually outlined in regulation regulation Details of increased benefits for the urban living figure 3-4. environment Sea level rise Soil pollution Highlights of NBS in the built environment and the adaptation regulation added values they deliver in enhanced landscape Figure 3-3: NBS functions chart ecology of the city and in daily experience of the living Drought Air pollution environment of people. regulation regulation Landslide Water pollution regulation regulation Special techniques for the NBS Illustrations that zoom in on different specific NBS applications and techniques within the NBS family, including alternative design options and techniques. 32 33 BENEFITS 3. Urban considerations comprise suitable urban density, preferred land use, the relative size of the required area, and potential for integration with urban agendas. Urban density is rated from low to high based on the number of dwellings and the availability of open space. Area is rated from small to extra-large and is based on the required area of a specific This section describes multiple ways NBS can deliver social, economic, and environmental benefits. Each NBS family NBS to be effective. Normally, a nature-based solution with small area requirements has potentially high replicability chapter contains a list of selected benefits that are highlighted and explained (figure 3-6). The relative importance of rates, while a nature-based solution with extra-large area requirements is usually site-specific. benefits is graphically presented in a radar chart scored qualitatively to distinguish benefits that are considered least relevant, somewhat relevant and highly relevant for each NBS family (figures 3-5 and 3-7). 4. Maintenance comprises basic guidance on requirements such as intensity of labor, frequency, or special care in the initial stages of development. Figure 3-5: Radar graph for NBS benefits Coastal Stimulate Figure 3-8: Suitability considerations icons flood risk local economies reduction and job creation Pluvial Human Environmental flood risk reduction health Location and Hydrology Soil Contamination Water Sources Hydrologic Upstream climate quality of water connectivity retention NBS Family Riverine flood risk Education reduction Hydroperiod Landscape Salinity Inundation Wave Sedimentation Wave integration time exposure rate velocity Heat stress reduction Biodiversity Figure 3-7: Scale of measurement Resources production Cultural Planting and Slope Site evaluation Dimensions Hybrid infrastructure Species Species growing strategy and selection combination preparation highly Tourism and Social relevant recreation interaction somewhat Seedling Time of Construction Arable Natural Substrate Roof type Roof slope Technical relevant and planting production fabrics Carbon storage and tree production sequestration least relevant Figure 3-6: Benefits icons Structural Facade Accessibility Accessibility Inclusivity Vandalism Social Utility capacity orientation (humans) (vehicles) and crime involvement restrictions prevention SUITABILITY CONSIDERATIONS This section describes considerations of location suitability of NBS to help understand whether an NBS is suitable at Infrastructure Crop type Mosquitoes Floodplain Riverbanks Natural a location in or around a city. Suitability considerations that are relevant for the feasibility and implementation of the restrictions profile regeneration NBS family, are subdivided in four categories (figure 3-8): 1. Environmental considerations comprise factors such as location and climate, hydrology and soil characteristics. Urban 2. Technical considerations cover a variety of considerations dependent on the NBS, such as effective dimensions, planting and growing strategy, and synergies with gray infrastructure. Land use Urban Area Integrated density urban planning 34 35 COSTS This section consists of two elements: 1. Cost considerations: 1. Land; 2. Construction and implementation; 3. Maintenance. Land Construction and Maintenance Implementation 2. Unit cost examples from around the globe. NBS IN PRACTICE This section provides examples of NBS with global good practices, lessons learned, and guidance for learning how to successfully finance, implement, and maintain NBS. The examples are from existing NBS projects, literature review, and case studies that have identified as good practices throughout the globe. Every example selected comprises an image, project name, year, location, brief description, benefits, source, website link for detailed information, and key aspects which highlight the significance of the NBS in a specific context (figure 3-9). Community Educational Integrated involvement scope with housing development Figure 3-9: Examples of key aspects of NBS implementation A recreational corridor in Seoul, South Korea Photo by Daniel Bernard on Unsplash 36 37 3.2 Urban NBS Families 42 Urban Forests Bioretention Areas 140 56 Terraces and Slopes Natural Inland Wetlands 154 70 River and Stream Renaturation Constructed Inland Wetlands 168 84 Building Solutions River Floodplains 182 98 Open Green Spaces Mangrove Forests 196 112 Green Corridors Salt Marshes 210 126 Urban Farming Sandy Shores 224 38 39 An urban wetland park in Nugegoda, Sri Lanka Photo by Shruthimathews on Flickr 40 41 FACTS AND FIGURES DESCRIPTION Urban forests are complex ecosystems with a remarkable capacity for regeneration and resiliency (FAO 2016). Urban forests are located within cities or at the rural–urban interface. In most contexts, urban forests survive and thrive as fragments of the larger regional landscape mosaic, or emerge as pockets of successional outgrowth on vacant or abandoned land. Urban forests adapt to adversity and have the ability to survive in hostile conditions. Varied in size and composition, they demonstrate remarkable resilience under a great deal of stress from pollution, compacted soils, and disrupted hydrological cycles. In addition, urban forests may be subjected to intentional and unintentional abuse from fires, harvesting, logging, encroachment, and adverse chemical impacts. The combination of trees, shrubs and grasses, the complexity of soils, and related biotic and abiotic components give urban forests a strong advantage as rich and vital sources of biodiversity. Multiple mechanisms of adaptation make them one of the most valuable nature-based solutions. Urban forests have a great potential to mitigate the urban heat island effect and air pollution, and to retain stormwater. They protect rivers by intercepting rainfall, increasing infiltration, and reducing flooding. In addition, they clean soils, sequester carbon, and regulate water cycles through retention, infiltration and evapotranspiration; improve air and water quality; provide critical habitat for a variety of species, and decrease ambient temperatures. Urban forests make positive contribution to the physical, mental, social, and economic wellbeing of urban societies. Their preservation and maintenance are a critical opportunity to make cities and communities resilient to climate change. Acknowledging that "urban forests can be defined as networks or systems comprising all woodlands, groups of trees, and individual trees located in urban and peri-urban areas; they include, therefore, forests, street trees, trees in parks and gardens, and trees in derelict corners” (UN FAO), the tunneled perspective in this chapter on urban forests focuses only to support cities with this specific NBS family. TYPE OF CITY SCALE APPROACH Protect Neighborhood Conserve existing forest areas. Coastal Delta Rehabilitate, Restore, Enhance City Reforest and manage existing forest areas. Create River basin Plant new forest areas. River Mountain PROCESSES Evapotranspiration Cooling effect Carbon sequestration Air cleaning Shade Biodiversity Infiltration URBAN FORESTS Soil cleaning Bojong Genteng, Indonesia Aquifer recharge Photo by Vickry Alvian on Unsplash 42 43 VISUALIZATIONS VISUALIZATION OF URBAN FORESTS IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR URBAN FORESTS 2 Phytoremediation forest A phytoremediation forest consists of trees and shrubs with specific metabolic qualities that allow such vegetation to clean polluted soils inclusive of those on landfills and abandoned urban areas. The roots and microorganisms remove, transfer, stabilize, or detoxify contaminants in the soil and groundwater, improve ecological conditions, and help prepare sites for future development. 1 3 Ecological forest corridors Urban forests are often established along drainage lines where additional moisture is available. These forests provide a critical linkage, while screening light and noise effects, allowing safe movement of species in the landscape. Ecological forest corridors can also be established in upland areas to link important habitats. Where possible, these forests should include structural complexity and species diversity to facilitate movement of a broad suite of species. Details of increased benefits for the urban living environment 1 2 3 Agroforestry Agroforestry is a dynamic and ecologically based natural resource management system. Agroforestry integrates trees and wooded patches into farms and productive landscapes, and diversifies and enhances agricultural production. Increased social, economic, and environmental benefits can be derived from any productive area Urban forests reduce heat Urban forests provide Urban forests should be where trees contribute to the productivity of the landscape within by providing shade and opportunities for people to developed using a suite of and outside cities (FAO 2021a). evaporative cooling. retreat from the city and enjoy native species to optimize recreational activities such as biodiversity values. walking and cycling. 44 45 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of urban forests. The diagram in this section shows a sampling of important benefits that urban forests can provide to people. Pluvial and Riverine flood riverine flood regulation risk reduction Heat stress risk reduction Pluvial flood regulation Resources Biodiversity production Subsidence regulation URBAN FORESTS Heat regulation Air pollution Tourism and regulation recreation Soil pollution regulation Biodiversity Carbon storage and Human health Landslide sequestration regulation Pluvial and riverine flood regulation: Urban forests absorb and retain significantly more stormwater than paved surfaces. Trees and Pluvial and riverine flood risk reduction: Well-managed and a reduction in the cost of healthcare and improved productivity soils of forested areas intercept precipitation and recycle the water through evapotranspiration, root water uptake, and infiltration healthy forests can contribute greatly to reducing flood risks in (Buckley and Brough 2015). (Gehrels et al. 2016). Upland forests with deep soils can intercept and infiltrate rainwater, reducing flood hazards along canals and downstream areas. Forests are beneficial to retain stormwater Tourism and recreation: Urban forests create opportunities rivers downstream (Ozment et al. 2019). A review of restoration studies found that 83% of the cases reported a positive relation and decrease the amount of water rapidly washing over the for recreational activities such as walking and cycling especially between infiltration capacity and forest restoration in upland areas (Filoso et al. 2017). streets and public spaces, entering and overwhelming the in proximity to residential areas. Urbanization will result in a sewerage systemws. As a result, forests can lower flood heights higher demand for recreation opportunities and increased Heat regulation: Urban forests reduce heat island effects by shading building surfaces, deflecting radiation from the sun, and and flood velocities in surrounding areas, thereby reducing visitor numbers in urban forests. releasing moisture into the atmosphere. Shaded surfaces may be 11–25°C (20–45°F) cooler than peak temperatures of unshaded structural damages to properties and infrastructure (Salbitano Carbon storage and sequestration: Urban forests store and materials. Evapotranspiration, alone or in combination with shading, can help reduce peak summer temperatures by 1–5°C (2–9°F) et al. 2016). sequester carbon in the above ground vegetation and in the (EPA n.d). Heat stress risk reduction: Trees reduce heat in the built soil, providing climate change mitigation benefits. Stored environment by providing shade and evaporative cooling. carbon densities per hectare vary greatly as a result of climatic Other functions: Tree root systems stabilize soils. This is particularly important in areas with high risk of erosion such as riparian Forest areas within the city boundaries reduce solar conditions, soil conditions, and forest management. A recent zones and steep slopes. Forested areas reduce soil subsidence, mitigate air and soil pollution, and provide habitat and conduits for radiation, by providing shade, and air temperature through review of natural regeneration—successional forests, secondary the movement and propagation of local fauna (Brockerhoff et al. 2017). evapotranspiration (EPA n.d.). Reducing extreme heat in cities forests, and forest restoration—showed that regeneration brings a variety of socioeconomic benefits, including reduced delivers significant carbon sequestration benefits estimated at mortality (Tan et al. 2010), improved health, reduced energy 9.1–18.8 tons CO2 per ha per year for the first 20 years of growth. cost and carbon dioxide emissions (Roxon et al. 2020), and With continued biomass growth, these rates can be as high or improved productivity of labor (Wong et al. 2017). higher after the first 20 years of forest regeneration. Rates are Resource production: If managed sustainably, forests can typically lower in temperate than in tropical regions, suggesting provide a variety of natural resources: fruit and vegetation, that latitude is an important general driver of biomass growth animals, biomass and timber, genetic material for all types of (Bernal et al. 2018). biota, fuel, and medicinal plants (Brockerhoff et al. 2017). Biodiversity: Forests and woodlands support a range of Human health: Urban forests offer physical, emotional, and terrestrial and aquatic biodiversity. Wet tropical forest regions mental health benefits to local communities in different ways, are home to the richest diversity of species in the world (Hassan including: increased immune responses (Kuo 2015; Li et al. et al. 2005; Lindenmayer 2009; Gibson et al. 2011). Besides the 2008); benefits for focus and attention (Kaplan 1995); and intrinsic value of biodiversity, the species that are part of the accelerated rates of recovery from illnesses (Ulrich et al. 1991; forest ecosystem support its tourism and recreation value. Alvarsson et al. 2010). These positive health effects often lead to 46 47 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: New urban forests can be planted anywhere in the world (FAO 2021b). Forests al. 2015). The availability of a nursery or other sources that can produce quality trees, following a good intended to reduce stormwater runoff can be effective in a broad range of climates and significant results seedling preparation process, is therefore critical for forest establishment (Evans and Turnbull 2004). can be achieved within 15 to 20 years after planting. In dry climates, however, afforestation must be Easily cultivated seedlings are not always the most desirable, and incentives, financial or otherwise, implemented with greater care to avoid lowering water tables and reducing soil recharge rates especially should be used to encourage the growing of desirable species to desirable sizes and parameters. during the dry season. In contexts where water is critical to tree growth, artificial irrigation may be required to sustain forest establishment and maintenance. Planting and growing strategy: Humans, free-range livestock, and land management practices in urban settings can subject seedlings or young trees to additional removal, destruction, and browsing challenges, Soil: Soils provide water and nutrition, and act as a substrate or a medium for the trees to grow (Le et which require a sustainable planting and growing strategy. Planting on deforested or degraded sites al. 2012). New trees require the substrate to have high mineral and structural quality. The type and requires sturdy plants from the nursery, which are well-watered before planting (FAO 2021b). Planting composition, depth, acidity, and the degree of compaction are all major substrate considerations. Sandy in urban settings—especially for urban forests with intended human uses and in areas with gray and loamy soils provide better conditions for new forests given their strong infiltration capacity and infrastructure—often requires additional considerations of seedling or tree sizes, pre-planting, formative aeration of the soil. Soils with a high proportion of clay and compact soils are much less favorable to the pruning, and root management, proximity of planting to gray infrastructure, and identification of other establishment of the new roots (Kadam et al. 2020). growing and planting parameters to ensure the most sustainable planting initiative. TECHNICAL Time of planting: To survive, the seedlings must be planted at the right time of the year (Nawir and Rumboko 2007). In most parts of the world that means the beginning of the rainy season. Tree planting can extend into the middle of the season as long as newly planted trees receive adequate amount of Slope: The direction of the slope is an important consideration in temperate regions. Slopes are moisture during the first months while they develop their root systems (Le et al. 2012). responsible for variations in soil humidity, determining the velocity of stormwater runoff, and the rate of erosion of soils. Unstable soils and steep slopes can be challenging during the initial phase of growth when trees are establishing the roots (Kadam et al. 2020). Once the initial challenge is surpassed, forests URBAN thrive and frequently occur on steep slopes where the cost of construction is too prohibitive for urban development. Site evaluation and preparation: Site preparation may require suppression and removal of weeds, Land use: Suitable land uses for urban forests: Afforestation of degraded natural forest areas, possibly cultivation and fertilization, augmentation of soil structure and composition (Le et al. 2012). In alluvial sites along streams, rivers, and water bodies, steep slopes at risk of soil erosion and landslides, areas without established vegetation, it may be necessary to establish nurse crops of fast-growing species non-productive agricultural sites, and no longer productive industrial wood plantations (FAO 2021b). before planting preferred species (FAO 2021b). Species selection: Identifying the desired type of urban forest and its ultimate objectives are important Urban density: Urban forests are suitable for low to medium density urban areas. in supporting the selection of tree species, establishment of a planting and growing strategy, and the implementation of each urban forest. Future mature forest objectives could include carbon sequestration, slope stabilization, heat stress mitigation, flood mitigation, biodiversity enhancement, and other technical factors as well as aesthetics, recreational, and public space uses, costs for implementation Area: Small to extra-large. Whereas regional afforestation programs are ideally planned at a landscape or and maintenance. Additional objectives may include the provision of livelihood and income generation city scale, small forests also offer biodiversity and other benefits . opportunities for local communities. Species selection can be tailored to the suitability of each identified species option according to each specific site, with local indigenous tree species always being preferable (Le et al. 2012). Integrated urban planning: New forests can become an integral component of conservation zones, slope Species combination: As a general recommendation, newly established forests should be composed of a stabilization measures, and the development of green areas and public parks. mix of local tree and understory species. It is important that forests are not established on untransformed land that already supports indigenous vegetation as such areas contribute to the conservation of other non-forest species and ecosystems. When forests are established, a mix of species should be used that mimics natural forest habitat in the region. Such forests are more typically productive and resilient and MAINTENANCE offer higher levels of ecosystem services (Le et al. 2012). Seedling and tree production: Global urban forestry best practices are shifting to include—and in some For up to five years after establishment, tree seedlings may require watering or irrigation and need to be protected from cases require—the planting of larger saplings and trees rather than conventional seedling planting. Some weeds competing for light, moisture, and nutrients, and from grazing wild and domestic animals. Pruning and cutting may also cities have mandated a mix of size, age, planting distribution, species variety, and other requirements be required. In seasonally dry climates where fire poses a significant risk, an effective fire prevention program is essential. including, for example, that urban trees must be at least 1.5 to 3.0 meters tall at the time of planting for Dead seedlings should be replaced early in the next rainy season, ideally with seedlings of a similar size to those surviving seedling, sapling, or tree production. The growing, formative pruning, and establishment of seedlings, nearby (FAO 2021b) Silvicultural treatments applied at the establishment and early growth phase are particularly important saplings, and young trees in a nursery is the primary way of establishing planting stock in many parts of to forest establishment (Le et al. 2012). the world, although local communities may also be trained in growing indigenous seedlings (Douwes et 48 49 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land is Urban forest implementation costs The cost of forest maintenance required for urban forests. include tree inventory, securing can vary widely depending on the necessary government permits, site location of the urban forest, forest Land on which urban forests may be preparation (for example, draining, condition, and its age (newly planted located may be public or private. cleaning, weeding and invasive versus conserved mature forests) and species removal), and reforestation species composition of trees. Land required for urban forests (tree purchase, planting, watering, may span a spectrum of small to and pruning as required). Urban forest maintenance costs large parcels. Larger urban forest may include: areas may require engagement and cooperation with multiple • Training and capacity building landowners and stakeholders and can • Monitoring and additional raise transaction costs. inventory • Replanting, depending on tree mortality Example land-related costs: • Pruning or thinning • Acquisition costs • Invasive species removal • Land use (for example, payments • Tree disposal to landowners) costs • Tree or forest litter management • Land protection costs, including managing and controlling access • Community resettlement costs UNIT COST EXAMPLES THROUGHOUT THE GLOBE • Planting and 40-year maintenance costs for • Tree reforestation costs: US$2,400–US$3,500/ha urban trees in different cities of Colorado, US, (Strassburg and Latawiec 2014). were found to vary from US$100–$570 per tree. • A study in Ghana estimated ~US$8,000/year cost (McHale et al. 2007). of forest area within an urban university (Dumenu • Watershed reforestation from European cost 2013). data: US$2207/ha (US$185–US$5,546/ha) (Ayres • Operational costs of afforestation (for example, et al. 2014). maintenance, invasive species and pest control, • Capital costs of afforestation (planting, labor expenses) from a UK study: US$3,600– establishment, financing) from a UK study: US$3,700/ha (Cambridge Econometrics 2020) US$15,780–US$18,700/ha (Cambridge • U.S. cities spend US$13–US$65 annually per tree Econometrics 2020). (McPherson et al. 2005) Brasov, Romania Photo by Maria Teneva on Unsplash 50 51 NBS IN PRACTICE The projects in this section highlight good practices and lessons learned in four urban forest projects, drawn from a growing number of case studies around the globe. Campaign Project #1: Freetown the Tree Town Campaign, 2020–23 Project #3: Toronto Strategic Forest Management Plan, 2012–22 0 trees Location: Freetown, Sierra Leone Location: Toronto, Canada Description: Within and surrounding the urban space around Description: The City of Toronto recognizes the value of urban the capital, Freetown, trees have given way to buildings, a bleak forests and aims to increase its tree canopy cover to 40 percent. The testament to ongoing deforestation and environmental degradation City's focus is on maximizing the potential ecological, social, and in Sierra Leone. The Freetown Municipality began a one million tree- economic benefits of urban trees. The Urban Forestry branch of the planting campaign in 2020. In addition to diverse native tree species Parks, Forestry and Recreation division maintains over four million with extended canopies and strong roots, private compound and trees on public property and works with local groups and residents community-based trees include mango trees to provide additional to expand and improve the urban forest throughout the city. Since fruit harvesting community benefits. Educational workshops, 2013, the city has been planting approximately 100,000 trees on community-based stewardship, planting and growing models public lands—parks, streets, ravines—per year, with ambitions to establish ownership and value in the campaign at the community increase that to 300,000 trees per year through new private–public level. “This isn’t just about planting trees. It’s about growing trees, partnerships with private landowners. and it’s about ensuring that each one of us is part of the process,” Photo by World Bank says Yvonne Aki-Sawyerr, Mayor of Freetown. “A million trees is Photo by Matthew Henry on Unsplash Benefits our city’s small contribution to increasing the much-needed global Governance, Health, Biodiversity. carbon sink.” Source Benefits City of Toronto, Urban Forestry Education, Health, Biodiversity, Employment. https://www.toronto.ca/data/parks/pdf/trees/sustaining- Source expanding-urban-forest-management-plan.pdf Community Private and Environmental Equitable Increase Promote Freetown City Council involvement public scope stewardship for distribution awareness environmental sustainability https://www.betterplace.org/en/projects/82290-tree-planting- stewardship campaign-in-sierra-leone Project #2: Shandong Ecological Afforestation Project, 2010–16 Project #4: Urban Food Forest Rijnvliet, 2017 to date Location: Shandong, China Location: Utrecht, The Netherlands Description: Counties of the Shandong Province initiated the Description: Residents of the Rijksstraatweg and the revegetation of degraded mountainous areas through the planting Metaalkathedraal areas proposed the concept of a food forest in of trees and shrubs on highly degraded hillsides with a shallow soil the new urban development of Rijnvliet in 2017. The municipality cover. The main goal was to protect agricultural land, improve developed a public space for this purpose—the edible residential productivity, and stabilize a newly created alluvial plain near the area. All plantings were chosen for their value to nature, with mouth of the Yellow River. A protective layer of vegetation was strong preferences for edible plants and trees, even in the private established along the roads, the canals, and in areas designated residential gardens. The municipality has also accorded Rijnvliet for afforestation. The initiative aimed to strengthen project a central food forest of 15,000 m2, dedicated space built on seven management capacity of the local and provincial governments. multiple layers that form an integrated ecosystem. A neighborhood Participants received technical assistance, learn to monitor and orchard for recreational activities and play areas for children is also evaluate the results, and took part in study tours. in planning. Residents, the school, and the municipality regularly discuss fresh ideas to implement. Photo by World Bank Benefits Photo by Fieke Damen / Felixx Landscape Architects and Planners Governance, Education. Benefits Source Community, Food, Biodiversity, Awareness. World Bank Source https://www.worldbank.org/en/results/2017/07/26/china- Felixx Landscape Architects, The Zwarte Hond, AE Food Forestry afforestation-project-in-shandong-improves-environment-and- Development and Utrecht Municipality. Government Participatory Knowledge farmers-incomes Community Educational Integrated https://www.utrecht.nl/wonen-en-leven/bouwen/bouwprojecten/ leadership process development involvement scope with housing leidsche-rijn/buurten/rijnvliet/de-eetbare-woonbuurt/ for future development https://www.felixx.nl/projects/urban-food-forest-rijnvliet-utrecht. application html 52 53 REFERENCES Alvarsson, J.J., Wiens, S. and Nilsson, M.E. 2010. Stress recovery during exposure to nature sound and environmental Kuo, M. 2015. How might contact with nature promote human health? Promising mechanisms and a possible central noise. International Journal of Environmental Research and Public Health, 7(3)1036–46. pathway. Frontiers in Psychology, 6:1093. Ayres, A., Gerdes, H., Goeller, B., Lago, M., Catalinas, M., García Cantón, Á., Brouwer, R., Sheremet, O., Vermaat, J., Le, H.D., Smith, C., Herbohn, J. and Harrison, S., 2012. More than just trees: assessing reforestation success in tropical Angelopoulos, N. and Cowx, I. 2014. Inventory of river restoration measures: effects, costs and benefits. REstoring rivers developing countries. Journal of Rural Studies, 28(1)5–19. FOR effective catchment management (REFORM). Li, Q., Morimoto, K., Kobayashi, M., Inagaki, H., Katsumata, M., Hirata, Y., Hirata, K., Suzuki, H., Li, Y.J., Wakayama, Y. and Bernal, B., Murray, L.T. and Pearson, T.R.H., 2018. Global carbon dioxide removal rates from forest landscape restoration Kawada, T. 2008. Visiting a forest, but not a city, increases human natural killer activity and expression of anti-cancer activities. Carbon Balance and Management, 13:22. https://cbmjournal.biomedcentral.com/track/pdf/10.1186/s13021- proteins. International Journal of Immunopathology and Pharmacology, 21(1)117–127. 018-0110-8.pdf Lindenmayer, D.B. 2009. Forest wildlife management and conservation. Annals of the New York Academy of Sciences, Brockerhoff, E.G., Barbaro, L., Castagneyrol, B., Forrester, D.I.,Gardiner, B., González-Olabarria, J.R., Lyver, P.O.B., 1162(1)284–310. Meurisse, N., Oxbrough, A., Taki, H. and Thompson, I.D. 2017. Forest biodiversity, ecosystem functioning and the provision of ecosystem services. https://link.springer.com/content/pdf/10.1007/s10531-017-1453-2.pdf Lupp, G., Förster, B., Kantelberg, V., Markmann, T., Naumann, J., Honert, C., Koch, M. and Pauleit, S. 2016. Assessing the recreation value of urban woodland using the ecosystem service approach in two forests in the Munich metropolitan Brown, S., Sathaye, J., Cannell, M. and KAUPPI, P.E. 1996. Mitigation of carbon emissions to the atmosphere by forest region. Sustainability, 8(11)1156 management. The Commonwealth Forestry Review, 80–91. https://www.jstor.org/stable/42607279 McHale, M.R., McPherson, G.E., and Burke, I.C. 2007. The potential of urban tree plantings to be cost effective in carbon Buckley, R.C., and Brough, P. Economic Value of Parks via Human Mental Health: An Analytical Framework. Front. Ecol. credit markets. Urban Forestry & Urban Greening, 6(1)49–60. Evol., 2017. https://www.frontiersin.org/articles/10.3389/fevo.2017.00016/full McPherson, G., J.R. Simpson, P.J. Peper, S.E. Maco, and Q. Xiao. 2005. Municipal forest benefits and costs in five US Cambridge Econometrics, Royal Society for the Protection of Birds. Economic costs and benefits of nature-based cities. Journal of Forestry,103:(8)411–416. solutions to mitigate climate change. 2020. https://www.camecon.com/wp-content/uploads/2021/03/The-economic- costs-benefits-of-nature-based-solutions_final-report_FINAL_V3.pdf Nawir, A.A. and Rumboko, L., 2007. Forest rehabilitation in Indonesia. Center for International Forestry Research. SMK Grafka Desa Putera, Jakarta, Indonesia. Dumenu, W. K. 2013. What are we missing? Economic value of an urban forest in Ghana. Ecosystem Services, 5:137– 142. Ozment, Suzanne; Ellison, Gretchen; Jongman, Brenden. 2019. Nature-Based Solutions for Disaster Risk Management. Washington, D.C. World Bank Group. http://documents.worldbank.org/curated/en/253401551126252092/Booklet Environmental Protection Agency of the US (EPA). Using Trees and Vegetation to Reduce Heat Islands. https://www.epa. gov/heatislands/using-trees-and-vegetation-reduce-heat-islands Raftoyannis, Y., Bredemeier, M., Buozyte, R., Lamersdorf, N., Mavrogiakoumos, A., Oddsdóttir, E. and Velichkov, I., 2010. Afforestation Strategies with Respect to Forest–Water Interactions. In Forest Management and the Water Cycle. Evans, J. and Turnbull, J.W., 2004. Plantation forestry in the tropics: The role, silviculture, and use of planted forests for 225–245. Springer, Dordrecht. industrial, social, environmental, and agroforestry purposes (No.3. ed.). Oxford University Press. Roxon, J., Ulm, F.-J. and Pellenq, R.J.-M. 2020. Urban heat island impact on state residential energy cost and CO2 FAO. 2016. Guidelines on urban and peri-urban forestry. F. Salbitano,F., Borelli, S., Conigliaro, M., and Chen, Y. FAO emissions in the United States. Urban Climate, 31:100546. https://www.sciencedirect.com/science/article/abs/pii/ Forestry Paper No. 178. Rome, Food and Agriculture Organization of the United Nations. S2212095518303560 FAO. 2021a. Agroforestry. Food and Agriculture Organization of the UN. http://www.fao.org/forestry/agroforestry/en/ Strassburg, B.B. and Latawiec, A.E. 2014, March. The economics of restoration: costs, benefits, scale and spatial aspects. In CDB Meeting-Linhares: International Institute for Sustainability. FAO. 2021b. Sustainable Forest Management Toolkit. Food and Agriculture Organization of the UN. http://www.fao.org/sustainable-forest-management/toolbox/modules/forest-restoration/in-more-depth/en/ Salbitano, F., Borelli, S., Conigliaro, M. and Chen, Y., 2016. Guidelines on urban and peri-urban forestry. FAO Forestry Paper, 178. Filoso, S., Bezerra, M.O., Weiss, K.C. and Palmer, M.A. 2017. Impacts of forest restoration on water yield: A systematic review. PloS One, 12(8). Tan, J., Zheng, Y., Tang, X., Guo, C., Li, L., Song, G., Zhen, X., Yuan, D., Kalkstein, A.K., Li, F., and Chen, H. 2010. The urban heat island and its impact on heat waves and human health in Shanghai. Int J Biometeorol, 54:75–84. https://doi. Gehrels, H., van der Meulen, S., Schasfoort, F., Bosch, P., Brolsma, R., van Dinther, D., Geerling, G.J., Goossens, M., org/10.1007/s00484-009-0256-x Jacobs, C.M.J., Kok, S., and Massop, H.T.L. 2016. Designing green and blue infrastructure to support healthy urban living. TO2 federatie. http://www.adaptivecircularcities.com/wp-content/uploads/2016/07/T02-ACC-WP3-Green-Blue- Taylor, A.F., Kuo, F.E., Spencer, C. and Blades, M. 2006. Is contact with nature important for healthy child development? infrastructure-for-Healthy-Urban-Living-Final-report-160701.pdf State of the evidence. Children and their environments: Learning, using and designing spaces, 124. Gibson, L., Lee, T.M., Koh, L.P., Brook, B.W., Gardner, T.A., Barlow, J., Peres, C.A., Bradshaw, C.J., Laurance, W.F., Lovejoy, Ulrich, R.S., Simons, R.F., Losito, B.D., Fiorito, E., Miles, M.A. and Zelson, M. 1991. Stress recovery during exposure to T.E. and Sodhi, N.S. 2011. Primary forests are irreplaceable for sustaining tropical biodiversity. Nature, 478(7369)378– natural and urban environments. Journal of Environmental Psychology, 11(3)201–30. 81. Wong, L.P., Alias, H., Aghamohammadi, N., Aghazadeh, S., and Sulaiman, N.M.N. Urban heat island experience, control Hassan, R., Scholes, R. and Ash, N. 2005. Ecosystems and human well-being: Current state and trends. Island Press. measures and health impact: A survey among working community in the city of Kuala Lumpur. 2017. Sustainable Cities and Society, 35:660–68. https://doi.org/10.1016/j.scs.2017.09.026 Kadam, A., Umrikar, B., Bhagat, V., Wagh, V. and Sankua, R.N. 2020. Land Suitability Analysis for Afforestation in Semi- arid Watershed of Western Ghat, India: A Groundwater Recharge Perspective. Geology, Ecology, and Landscapes, 1–13. Kaplan, S. 1995. The restorative benefits of nature: Toward an integrative framework. Journal of Environmental Psychology, 15(3)169–82. 54 55 FACTS AND FIGURES DESCRIPTION Civilizations across the globe have been building landscape terraces to stabilize slopes for centuries and protect urbanized areas with steep slopes and loose soils, often exposed to a variety of hazards. These may include hydrometeorological hazards, such as floods, cyclones, and droughts, as well as gravitational hazards, like landslides and mudslides. Such gravitational hazards can cause disruption of transportation networks, loss of property and agriculture, sedimentation and pollution of the water bodies, blocked streets and infrastructure, and clogged stormwater systems. During a landslide, fast-moving debris can cause extensive damage. Many typologies and technical approaches for terracing exist, tailored to specific conditions and geographical characteristics of a location. Terracing technology is often developed to enable and to prevent land degradation and erosion simultaneously. To date, it is an efficient solution to control erosion and it provides additional advantages for agriculture, such as added soil depth and the possibility of managing water levels. Modern technology including geogrids, textiles, membranes, and barriers evolved to augment and enhance terracing practices tested over time. Bioengineered substrates and reinforcement materials have been developed to provide better growing medium for trees, shrubs, and herbaceous species that enhance the stability of the slopes. Other tools are available to electronically monitor and control water levels and check water and soil quality and nutrient content. TYPE OF CITY SCALE APPROACH Protect Neighborhood Preserve existing terrace systems. Coastal Delta Rehabilitate, Restore, Enhance City Restore existing terraces. Apply modern landscape technologies, including membranes and geo- textiles. River basin River Mountain Create Design new terraces with built-in long-term sustainability criteria. PROCESSES Cooling effect Water storage and reuse Evapotranspiration Biodiversity Soil stabilization Water delay Overflow Infiltration Soil and water TERRACES AND SLOPES cleaning Aquifer recharge Bali, Indonesia Photo by Guille Álvarez on Unsplash 56 57 VISUALIZATIONS VISUALIZATION OF TERRACES AND SLOPES IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR TERRACES AND SLOPES Living smiles A living smile is a natural porous fence made of flexible plant cuttings, installed to drain a terrace of the excess water, simultaneously capturing and retaining suspended sediment, which is incorporated into the existing soil. Additional sediment increases the volume 1 3 and structure of the existing soil, enhancing its quality as a growth medium. As a landscape technology, the living smile protects terraces from losing too much soil during heavy storms and protects plant roots from being exposed (Polster 2008). 2 Wattle fences A wattle fence is made of sturdy wooden posts driven vertically into the soil with pliable young shoots woven horizontally in between. Traditionally made of willows or similar young trees, it is an ancient technology that is affordable, quick, and easily applied. Wattle fences are installed as vertical breaks perpendicular to the slope to reduce the impact of rolling materials during a storm. They also act as short retaining walls to reduce the angle of a slope and help Details of increased benefits for the vegetation establish. The cuttings sprout and grow, reinforcing the urban living environment overall structure (Polster 2008). 1 2 3 Vegetated gabions Vegetated gabions are rectangular baskets made of heavily galvanized steel or another durable, corrosion resistant wire mesh, filled with stones. Gabions can be reinforced with geotextiles and filled with earth. They are used to reinforce and protect the slopes from fast-moving stormwater. By virtue of their initially porous Terraces stabilize areas affected The design of terraces continues Terraces are entirely man-made structure, gabions capture and incorporate some of the flowing by flooding and landslides, while centuries-old tradition, passing landscapes that rely on a continuous debris and sediment into their structure, which becomes a growth creating safe spaces for recreation technical knowledge and cultural commitment of people for their medium for plants that colonize and reinforce the gabions (Polster and other uses. traditions, integrating new upkeep. They have symbolic meaning 2008). technologies and preserving local and represent a cultural practice that customs. binds people to their natural context. 58 59 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of terraces and slopes. The diagram in this section shows a sampling of benefits that terraces and slopes can provide to people. Water quality and sediment Pluvial flood, management landslide and erosion risk reduction Pluvial flood regulation Cultural Landslide Resources production Biodiversity regulation TERRACES AND SLOPES Drought regulation Soil pollution Tourism and regulation recreation Water pollution regulation Pluvial flood regulation, erosion and landslide control: Traditionally, landscape terracing has been used in regions with steep Pluvial flood, landslide, and erosion risk reduction: Terracing historic significance, terraces generate additional revenue from topography and poor soils to increase the size of arable land and stabilize soils simultaneously (Berčič and Ažman-Momirski 2020). transforms the overall length of a slope into a series of short, tourism, including income from local restaurants, hotels, and Terraces conserve water and soil by keeping them in place. They have the ability to capture and store stormwater and slowly release relatively level steps. Since each step is positioned perpendicular hospitality services (Díaz et al. 2019). the excess. The detention function of terraces is of increasing importance as more extreme precipitation events are occurring as a to the flow of water, it absorbs a certain amount and drains Biodiversity: Cultivated terraces maintain high levels of soil result of climate change. Terraces can be managed to improve their detention and infiltration capacity (Eekhout et al. 2018). the excess to the next step down (Díaz et al. 2019). This way, moisture and nutrient content. The plants, unless they grow much of the soil and its nutrient content is preserved in situ in the gabions, may be perceived as a threat, yet terraces can A study conducted in India demonstrated the efficacy of terraces in reducing runoff and soil loss by more than 80% compared to and the overall system not only reduces the risk of flooding safely provide habitat for certain birds. In the Mediterranean unterraced slopes (Díaz et al. 2019). In addition, a Canadian study found that terracing reduced runoff of seasonal rainfall by 25% downstream, but minimizes the amount of suspended soil in the region, for example, birds build nests on the terraces of rain- (NWRM n.d.). The traditional terracing in Veneto, Italy, reported a 50% increase in stormwater storage capacity by the terraces stormwater runoff, and protects infrastructures like irrigation fed arboreal crops and vineyard terraces shelter endangered (NWRM n.d.). channels, reservoirs, street drainage, the sewerage system spiders (Tokuoka and Hashigoe 2015). from being damaged and clogged by the sediment (Sandor and Cultural: Terraces represent cultural practices dating back Other functions: Terraces improve soil and water quality. Water quality increases due to improved buffering and filtering, thereby Eash 1995). Hence, proper functioning terraces avoid structural millennia. They are some of the most spectacular and enduring reducing groundwater and river pollution, and providing an extra supply of water to face periods of drought (Díaz et al. 2019). damages from pluvial flooding to the agricultural and irrigation achievements of human civilization recognized by UNESCO. infrastructure as well as to properties downstream. Besides (Díaz et al. 2019). As an agricultural practice, terraces help reducing flood risk, terraces reduce landslide risk. preserve ancient methods and practices passed from generation Resource production: Terrace farming ensures food security to generation. As such, they are both physical artifacts and part and increases crop yield 2.5 times by conserving water and of the intangible cultural heritage. soil (Haas et al. 1996; Hammad et al. 2004). In some instances, Water quality and sediment management: Considered highly the production is not limited to the crops. Rice paddies for effective techniques for erosion control, terraces trap sediment example, provide habitat for various edible aquatic animals. at each level of the steps where it becomes incorporated as the Terraces capture and clean stormwater, which can be reused growing medium for the crops. They also capture and infiltrate for additional purposes. large volumes of water and incrementally discharge the excess Tourism and recreation: Terraces are part of the cultural water so that it gets filtered by several terraces. Terracing is identity of many regions. They contribute to the scenic beauty of considered as a powerful water-harvesting technique (Rashid landscapes that attract tourists and inspire cultural production et al. 2016). In temperate climates, terraces work to conserve in the form of photography, painting, and film. In some regions water, and facilitate groundwater recharge (Liu et al. 2004). that are appreciated for their exceptional beauty and and 60 61 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: Terraces can be found almost everywhere in the world, but they are very different Arable production: Terrace farming improves soil fertility and land productivity and decreases the amount in use, size, shape, and construction. They can be used as a land management instrument to prevent of horizontal surface required to meet the local demand for crops. Terraces are therefore suitable for erosion and mudslides, but are more commonly used in combination with agriculture. Terraced barley, any hilly area with dense population, food shortages, and high unemployment rates; and areas where wheat, and rice paddies for example, are abundant in southeast Asia, and South America where rains are traditional local crops require plentiful irrigation or permanent water levels, such as rice and taro (Mesfin frequent and there is usually an excess of water. In the drier climates of Africa and in the Mediterranean 2016). region, terraces are built for vineyards, olive groves, and orchards as well as to grow cork oaks and other crops (Berčič and Ažman-Momirski 2020). URBAN Hydrology and soil: Terraces are built perpendicular to the flow of water to reduce erosion, retain soil and moisture, create space for the crops, and generate a favorable microclimate to increase crop yield. The dynamic nature of terrace water-and-soil cycles helps maintain long-term soil fertility and requires areas with relatively deep soils, sites that are not dissected by gullies, and not too stony (FAO 1990). Different types of structural design for terraces can be applied in variety of conditions: For example, Land use: Suitable land uses for terraces are peri-urban green areas, agricultural areas, slopes, and green level bench terraces are generally used in areas with medium rainfall and highly permeable soils. Most areas. of the stormwater falling on these terraces is absorbed; the excess water is drained out. Outward sloping bench terraces or orchard-type bench terraces are typical of the low-rainfall areas with moderately permeable soil. Inward sloping bench terraces are typically constructed in areas with heavy rainfall and less permeable soils. A large portion of the rainwater is drained off through a drainage channel located Urban density: Terrace construction is suitable for low to medium density urban areas. on the inner side of the side of the terrace (Mesfin 2016). TECHNICAL Area: Medium to large. Terraces are nature-based solutions typically designed for application at a medium to large scale. Slope: The optimal slope and the ideal distance between terraces on slopes with different gradients and Integrated urban planning: Terraces can be an integral component of slope stabilization works, local food the analysis of existing practices can yield valuable information on what works in each region (Doreen production, development of green areas and public parks, and reforestation programs. and Rey 2004). Although a 50% slope is usually considered a threshold for making terraces (Green 1978), in Nepal terraces are made on slopes exceeding this limit, and cultivation is practised up to a 100% slope using contour terracing (Shrestha et al. 2004). Construction: Terrace construction is a labor-intensive land management practice. In any region, terracing must be done gradually at a regular pace, maintaining a careful balance between the cut and fill of soils MAINTENANCE (FAO 1990). Several construction methods are available: Terraces require regular care and maintenance. A small, neglected break can result in significant damage. Regular monitoring • Manual labor; the terrace must be built when the soil is neither too dry nor too wet. and maintenance should be carried out after heavy storms and harvests, especially in the first two or three years after • Construction using farmyard working animals and specialized tools. construction or restoration (FAO 1990). The use of monitoring equipment can reduce the number of inspections and expedite • Mechanized construction. the delivery of maintenance when it is needed. It is essential to design and maintain the proper slope for the individual terrace; secure proper installation of the drainage channels along the inner side of the terrace; identify the need for secure proper installation of any geotechnical membranes, living smiles, wattle fences, and gabions; and secure correct installation of electronic equipment for monitoring water level, chemicals, and temperature. Dimensions: The size of a terrace is defined by drainage requirements and method of agricultural cultivation, among other variables. Its length is limited to the size and shape of the lot. In humid tropical climates, a maximum of 100 meters in one direction is recommended for proper drainage. Nonmechanized cultivation limits the width to 2.5–5 meters; mechanized increases the width to 3.5–8 meters where depth of soil is not a limit (Mesfin 2016). 62 63 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land is Terrace construction costs will be The costs of terrace maintenance required for terraces in urban areas. impacted by soil conditions, the depend on the terrace typology, the degree and consistency of the slope local context, labor, and material Land on which terraces may be to be terraced, the length of terraces costs. located may be public or private. required, the material terraces are constructed from, and whether the Land required for terraces may terrace will be parallel or contour, range from small to large, requiring level or graded. different levels of engagement with landowners and stakeholders Costs of terrace construction include depending on the project area, and machinery (e.g., bulldozers, terrace affecting transaction costs. plows); labor (equipment operators; managers); materials (e.g., materials Example land-related costs: to make gabions, support terrace • Acquisition costs edges, and others); and mobilization • Land use (e.g., payments to equipment to move soil. landowners) costs • Land protection costs, including managing and controlling access • Community resettlement costs UNIT COST EXAMPLES THROUGHOUT THE GLOBE • A European study estimates the cost for new in the nursery and transplantation and manual terracing using heavy machinery at US$1,080 ha/ harvesting (Mishra and Rai 2011). year (Khulman et al. 2010). • A European study estimates the cost of terrace • The U.S. Natural Resources Conservation Service maintenance at US$242 ha/year (Khulman et al. (NRCS) provides a range of cost estimates for 2010). terraces from US$2.3–US$4.92/m of terrace. • In India, the total cost of construction and the first two years of maintenance has been estimated at US$1,600/ha, including preparation of the plants Cikawari, Indonesia Photo by Dian Herdiansyah on Unsplash 64 65 NBS IN PRACTICE The four projects in this section highlight best practices and lessons learned in terracing and slopes in rural areas, drawn from growing experience in implementing NBS throughout the globe. Project #1: Loess Plateau Watershed Rehabilitation Project, Project #3: Lesotho Climate-Smart Agriculture Investment Plan, 1994–2002 2012–20 Location: China Location: Lesotho Description: Home to more than 50 million people, the Loess Description: The Kingdom of Lesotho is a small mountainous Plateau in China’s northwest takes its name from the dry powdery country in South Africa. Its agriculture is based entirely on the wind-blown soil. Centuries of overuse and overgrazing led to one of mountain terraces. In addition to raising crops, most households the highest soil erosion rates in the world and widespread poverty. own livestock and cattle, indispensable to the cultivation of the Two projects over 12 years set out to restore China’s heavily terraces. When not grazing on summer cattle posts, away from degraded Loess Plateau in the early 1990s through one of the the village, livestock is kept at night in special enclosures, known world’s largest erosion control programs with the goal of returning as kraals, adjacent to the farmers' houses. The cattle and the this poor part of China to an area of sustainable agricultural terrace agriculture are part of the same agricultural ecosystem production. Terraces have reduced labor inputs and so, allowed that sustains life in Lesotho. Long-term success of its communities farmers to pursue new income-earning activities. The physical and depends on careful land management to preserve the delicate economic transformation of the Loess Plateau offers the clearest balance between the grazing and the crop-producing land. Photo by Momo on Flickr demonstration of what can be achieved through close partnership Photo by Simon Allen on Unsplash Benefits with the government, good policies, technical support, and active Economic resiliency, Culture. consultation and participation of the people. Source Benefits World Bank Income, Food, Water Quality and Sedimentation Management. http://documents1.worldbank.org/curated/ Example of Physical and Project principles Source Support Partnership with Building and en/847551575647928833/pdf/Lesotho-Climate-Smart-Agriculture- a fruitful economic widely World Bank to promote international promoting Investment-Plan-Opportunities-for-Transitioning-to-More- partnership transformation adopted and https://web.worldbank.org/archive/website00819C/WEB/PDF/ agricultural research capacity to access Productive-Climate-Resilient-and-Low-Carbon-Agriculture.pdf of agriculture replicated CHINA_LO.PDF transition institutes climate finance Project #2: Ifugao Rice Terraces, Ongoing Project #4: Radical Terraces, 1970s to date Location: Cordilleras, Philippines Location: Amaterasi y’indinganire, Rwanda Description: Built 2,000 years ago and maintained from generation Description: Unique to Rwanda, radical terracing is a terracing to generation, the Ifugao Rice Terraces represent an enduring method of cut and fill that results in reverse-slope bench terraces illustration of an ancient civilization that surpassed various with regularly shaped risers stabilized by grass or trees. Radical challenges and setbacks posed by modernization. The terraces terraces consolidate land to create permanent agriculture on the illustrate a persistence of cultural traditions, remarkable continuity, very steep slopes. Their objective is to improve the livelihood of the and endurance. The maintenance of the living rice terraces reflects farmers; restore and enhance environmental resilience by reducing a primarily cooperative approach of the whole community. It is the amount of soil being washed off, and improving the rates of based on detailed knowledge of the rich diversity of biological stormwater retention and infiltration. When making the terrace, resources of the Ifugao agroecosystem, a finely tuned annual the farmers isolate and preserve nutrient-rich topsoil from the slope system respecting lunar cycles, zoning and planning, extensive soil and incorporate it back into the reverse-slope bench. With help conservation, mastery of a most complex pest control regime based from external funding, 70% of land users have implemented radical on the processing of a variety of herbs, accompanied by religious terracing. Photo by Azilem-yongbi on Unsplash rituals. Photo by Manasse Nshimiyimana / Green Cover Initiative RWANDA Benefits Benefits Social, Education, Economy. Culture, Education, Economy. Source Source FAO World Heritage Conservation http://www.fao.org/3/a-au298e.pdf Community- Continuity of Generations https://whc.unesco.org/en/list/722/ External Community Boost local based land use cultural traditions of small-scale funding leadership in economy and and zoning and ecological farmers working execution and livelihoods plans knowledge as a community maintenance 66 67 REFERENCES Berčič, T. and Ažman-Momirski, L. 2020. Parametric Terracing as Optimization of Controlled Slope Intervention. Water, 12(3)634. Dorren, L. and Rey, F. 2004, April. A review of the effect of terracing on erosion. In Briefing Papers of the 2nd SCAPE Workshop, 97–108. C. Boix-Fayons and A. Imeson. Díaz, M.A.R., de Vente, J. and Pereira, E.D. 2019. Assessment of the ecosystem services provided by agricultural terraces. Pirineos, (174) 43. Eekhout, J.P., Hunink, J.E., Terink, W. and Vente, J.D. 2018. Why increased extreme precipitation under climate change negatively affects water security. Hydrology and Earth System Sciences, 22(11) 5935–46. FAO. Watershed Management Field Manual, Guide 13, Chapter 6 - Continuous Types of Terraces (Bench Terraces). n.d. http://www.fao.org/3/ad083e/ad083e07.htm Natural Water Retention Measures (NWRM). Traditional Terracing. http://nwrm.eu/measure/traditional-terracing Green, R. 1978. Integrated Watershed Management Torrent Control and Land Use Development Project. The construction and management of bench terracing system in the hill areas of Nepal. Haas, H.J., Willis, W.O. and Boatwright, G.O. 1966. Moisture Storage and Spring Wheat Yields on Level‐Bench Terraces as Influenced by Contributing Area Cover and Evaporation Control. Agronomy Journal, 58(3)297–99. Hammad, A.A., Haugen, L.E., and Børresen, T. 2004. Effects of stonewalled terracing techniques on soil-water conservation and wheat production under Mediterranean conditions. Environmental Management, 34(5) 701–710. Kuhlman, T., Reinhard, S. and Gaaff, A. 2010. Estimating the costs and benefits of soil conservation in Europe. Land Use Policy, 27(1)22–32. Liu, C.W., Huang, H.C., Chen, S.K. and Kuo, Y.M. 2004. Subsurface Return Flow And Ground Water Recharge Of Terrace Fields In Northern Taiwan. Journal of the American Water Resources Association, 40(3)603–614. Mesfin, A., 2016. A Field Guideline On Bench Terrace Design And Construction. Ministry of Agriculture and Natural Resources Natural Resource Management Directorate. Ethiopia. Mishra, P.K. and Rai, S.C. 2011. Cost-Benefit Analysis Of Terrace Cultivation In Sikkim Himalaya, India. www.researchgate.net/publication/338541387_Cost-Benefit_Analysis_of_Terrace_Cultivation_in_Sikkim_Himalaya_ India U.S. Natural Resources Conservation Service (NRCS). 2014. Public Cost Scenarios for Oklahoma, estimates FY2015. Compiled 11/18/2014. Available at: https://efotg.sc.egov.usda.gov/references/public/OK/CostSenarios_600Terrace.pdf Polster, D.F. 2008. Soil bioengineering for land restoration and slope stabilization. Course material for training professional and technical staff. Polster Environmental Services. Duncan. British Columbia. Rashid, M., Alvi, S., Kausar, R. and Akram, M.I. 2016. The effectiveness of soil and water conservation terrace structures for improvement of crops and soil productivity in rainfed terraced system. Pakistan Journal of Agricultural Sciences, 53(1). Sandor, J.A. and Eash, N.S. 1995. Ancient agricultural soils in the Andes of southern Peru. Soil Science Society of America Journal, 59(1)170–79. Shrestha, D.P., Zinck, J.A. and Van Ranst, E. 2004. Modelling land degradation in the Nepalese Himalaya. Catena, 57(2) 135–56. Tokuoka, Y. and Hashigoe, K. 2015. Effects of stone-walled terracing and historical forest disturbances on revegetation processes after the abandonment of mountain slope uses on the Yura Peninsula, southwestern Japan. Journal of Forest Research, 20(1)24–34. Puthucode, Kerala, India Photo by Aboodi Vesakaran on Unsplash 68 69 FACTS AND FIGURES DESCRIPTION In many urbanized areas around the world, rivers and streams became completely denaturalized. Construction of embankments, culverting, and filling in of tributaries became a normal practice in industrialized societies to create space for development. Globally, flood risk along rivers and streams steadily increased as a result of these ongoing economic developments in flood prone areas, in addition to the increased likelihood of extreme weather events owing to climate change. Increasing flood risk and the societal appreciation of ecosystem services and biodiversity have led to a paradigm shift in management of rivers and streams in urbanized areas, making the case for their renaturation and restoration. Several nature-based solutions have been developed to restore the natural dynamics of these watercourses. Renaturation—stream daylighting, reestablishment of riparian corridors, removal of concrete embankments, and river or stream bed and bank revegetation—are gaining momentum. Where possible, cities are more frequently reinstalling riparian corridors and other measures for renaturation, giving additional room for the rivers to flow. “Don’t fight the water, work with it,” is becoming entrenched in urban planning and drives river and stream renaturation projects. TYPE OF CITY SCALE APPROACH Protect Neighborhood Preserve the tree structure along rivers and streams. Coastal Delta Preserve and protect existing watercourses and City hydrological systems of rivers. River basin Rehabilitate, Restore, Enhance River Mountain Replant riverbanks. Daylight streams and tributaries. Rehabilitate rivers and stream to restore natural dynamic processes. PROCESSES Cooling effect Evapotranspiration Shade Biodiversity Soil stabilization RIVER AND STREAM RENATURATION Soil and water Infiltration cleaning South Korea Water buffer Photo by MJ Haru on Unsplash 70 71 VISUALIZATIONS VISUALIZATION OF RIVER AND STREAM RENATURATION IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR RIVER AND STREAM RENATURATION Bank and bed renaturation The riverbank is an interface of aquatic and terrestrial ecosystems, an area protecting cities from riverine floods and often an important social place with recreational and cultural value. Its renaturation design should also safeguard ecological functions and flood control. Riverbank and bed renaturation aim to restore the natural dynamic of the river, which may mean restoring its shape, creating physical 1 structures to direct the flow of water, and provide habitat for 3 aquatic species. 2 Stream daylighting Small streams provide a wide array of benefits to communities, such as nutrient and pollution removal, groundwater recharge, and flood mitigation. In some urban areas, streams were previously enclosed by concrete pipes or simply filled in. This could lead to floods, soil subsidence, and consequently to severe damages such as building collapses. Daylighting is a technique to remove layers of concrete and recreate the natural shape and dynamic of streams, resulting Details of increased benefits for the in increased wildlife and aquatic habitat, and better regulated urban living environment stormwater runoff treatment and intake (Eisenbert and Polcher 2020). 1 2 3 Bioengineering techniques Renaturation relies on several bioengineering techniques to recreate the natural course of a river and connect it to its landscape for floodplain and riparian corridor revegetation, riverbank stabilization, and restoration of the riverbed. The natural river dynamic rests on the use of plants, rocks, and other natural elements, as well River renaturation establishes a Stream renaturation returns streams People experience the river and its as geotextiles and membranes to create ecologically rich and meaningful relationship between to communities. It makes water a riparian corridor as one landscape, structurally stable environment mimicking natural conditions, while the city and its river. The new visible, valuable, and enjoyable part full of opportunities, recreation, and providing space for recreation (Eisenbert and Polcher 2020). public space provides recreational of daily life; an asset that protects and education, a year-round source of and cultural benefits, contributing invigorates. discovery. to the city's identity. 72 73 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of river and stream renaturation. The diagram in this section shows a sampling of benefits that river and stream renaturation can provide to people. Water quality and sediment management Riverine flood regulation Pluvial and riverine flood risk reduction Social interaction Pluvial flood regulation Biodiversity Bank erosion RIVER AND STREAM regulation Heat RENATURATION regulation Tourism and recreation Air pollution regulation Biodiversity Human health Water pollution Stimulate local economies regulation and job creation Pluvial and riverine flood regulation: River and stream renaturation can help slow the river flow and thus, reduce river floods Pluvial and riverine flood risk reduction: River and stream have specifically shown that visiting rivers, lakes, and other by creating water retention and infiltration capacity in the river system (Ozment et al. 2019). If natural functions are preserved renaturation projects can be effective as part of a large-scale waterbodies increases the sense of wellbeing (Helliwell et al. or restored—such as a river’s meandering path or vegetated riparian areas—a variation of flow and sediment movement leads urban water management strategy, in which a typical objective 2020). Renaturation projects created with safe spaces and to a reduction of the peak discharge (Soar and Thorne 2001). Stream restoration, when applied to an urban watershed, can be is to protect cities from floods by increasing the capacity of that promote active exercise, kayaking, walking, and biking, complemented by other NBS for stormwater management throughout the river basin to also reduce the magnitude of local pluvial waterbodies to hold excessive amounts of stormwater. Such contribute to mental and physical health (D'Haese et al. 2015). flood hazard. projects increase volumetric capacity and restore the natural These positive health effects often lead to a reduction in the cost hydrodynamics of the watercourses together with their river of healthcare and improved productivity (Buckley and Brough Heat regulation: Some specific forms of river and stream renaturation—such as restored riparian corridors including trees—stabilize banks, riparian corridors, buffer zones, and floodplains where 2015). water temperature and reduce ambient temperatures in adjacent neighborhoods. Such canopy-rich NBS are specifically effective for possible (NWRM n.d.). As a result, river and stream renaturation Biodiversity: River, stream, and riparian corridor restoration reducing extreme heat in high density urban areas or riparian areas used for recreation (Hathway and Sharples 2012). projects can lower flood height and flood velocity in surrounding projects are excellent ways to enhance biodiversity. The corridors areas and thereby reduce structural damages to properties and provide food, shelter, nesting, and breeding areas for wildlife, Other functions: River and stream renaturation can decrease pollution of water, soil, and air, stabilize soils and reduce soil erosion, infrastructure. and serve as safe conduits for the movement of biota within the and offset the loss of biodiversity by becoming critical conduits for the movement and propagation of biota (NWRM n.d.). Tourism and recreation: Stream and river renaturation create city and to the larger patches in the regional landscape mosaic. new recreational and tourism opportunities, from fishing and Social interaction: Daylighting and reshaping of hidden and boating to walking and bird watching, attracting urban dwellers artificially straightened watercourses result in attractive new to the waterfront. In some contexts, formal sports and recreation green and blue areas with plenty of opportunities for social areas can be integrated into buffer zones (NWRM n.d.). interaction. These urban spaces can, for example, be enlivened Stimulate local economies and job creation: Stream and with simple footpaths and are good locations for cultural events river renaturation in cities enhance flood safety, leading to to highlight the connection between the people and the river. the rise of property values in areas close to renaturated areas Water quality and sediment management: River and stream and potentially enable land value capture. Also, renaturation renaturation stabilizes riverbanks, prevents soil erosion, and projects increase the number of recreants and tourists, and reduces runoff. A riparian zone, for example, protects water thereby bring opportunities for local entrepreneurs contributing quality by capturing sediments and pollutants and prevents to urban economic growth. stormwater runoff from streets entering and contaminating Human health: Rivers and riparian areas are uniquely suited for a watercourse (NWRM n.d.). This may reduce adverse health active recreation, and as areas for contemplation and reflection effects of water pollution and reduce water treatment costs for pastime. These activities enhance the human experience in the city and downstream areas. cities and deliver important public health benefits. Studies 74 75 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: River and stream renaturation projects can be initiated anywhere river systems have Natural fabrics: River and stream renaturation may use a combination of geotextiles and other technologies been altered by development. They are particularly important in flood prone areas; areas characterized with natural elements such as stones, wood logs, and fascine mattresses for bed and bank protection and by high levels of impervious surface and runoff; and areas with vulnerable structures on top of culverted to control water movement along the stream (Eisenberg and Polcher 2020). streams (NWRM n.d.). Hydrology: The effectiveness of river and stream renaturation interventions depends on the hydrological conditions of a river system and the performance targets of the full suite of benefits. Seasonal flow URBAN characteristics and the capacity of the river to accommodate high discharge levels should be modeled to understand the capacity of the restored watercourse to retain floods and to inform bed and bank stabilization measures. Good hydrological and hydraulic models can be used to support the restoration of the natural dynamics of the river basin, evaluate appropriate renaturation techniques at targeted sites, and simulate the potential impact of climate change and planned future developments such as new urban development, construction of dams, or new wastewater outfalls. These variables may change the Land use: Multifunctional use, such as recreation, should be encouraged where possible as part of river quantity and timing of water flowing through the river as well as the potential consequences of flooding and stream renaturation projects to enhance the provision of benefits. events along the catchment. Soil: Soil characteristics of the riverbed, the banks, and the floodplain need to be examined when designing a renaturation project. Riverbank and floodplain soils must have enough structure to keep Urban density: River or stream renaturation projects can be implemented in both low and high urban plant roots in place during inundation. They must also have the right acidity and enough moisture to density areas. sustain the plants during droughts. Bank soils should be erosion resistant and can be reinforced by plants, geotextiles, membranes, and gabions, if needed. In some contexts, silt-laden riverbeds may require dredging to maintain the capacity and biodiversity values of the river (DEP 2006). Area: Medium to extra-large. River and stream renaturation is a nature-based solution appropriate for a TECHNICAL neighborhood, district, city and river basin scale. Slope: Riverbank and floodplain slopes intercept and assimilate pollutants from lateral stormwater Integrated urban planning: River and stream renaturation can be integrated into ecoconservation, water inputs. They also provide additional storage space for floodwaters that help protect the city in case the management, and the development or restoration of green areas or public parks. river overflows. Slopes also support riparian habitat that helps maintain temperature regime, sustain aquatic life, and serve as essential movement corridors for terrestrial biota. The slopes should maintain stability, so protection and stabilization are key elements to be considered when planning river and stream renaturation projects. MAINTENANCE Dimensions: The dimensions of a river renaturation project depend on the availability of land, the size of the stream or a river, and the goals of the project. The restoration of a riparian corridor and a buffer zone may extend tens of meters on both sides of the river (NWRM n.d.). Although wider buffer zones provide River and stream renaturation projects are particularly susceptible to damage during the first two to four years after greater benefits (DEP 2006), this is rarely possible in the urban context. The most frequently approved implementation (DEP 2006). Regular inspections should follow the progress of revegetation and check for any signs of minimum dimensions for buffers providing water quality and habitat maintenance are 10–30 meters erosion. Once vegetation is successfully established, maintenance frequency can be reduced, although regular control of (2030 palette 2020). A range of factors need to be considered when delineating a buffer zone such as invasive species, mowing, and monitoring for pests and diseases are recommended. Additional monitoring and maintenance flood risks, the profile of the banks, risks of pollution from adjacent land uses, and the need to generate are required during the first few years after inundation, and after any additional restoration efforts (DEP 2006). other benefits such as recreation and cultural value. Planting and growing strategy: As part of the riverine ecosystem, plants have several roles. They help reduce soil erosion and stabilize banks, enhance the quality and functions of riparian corridors and buffer zones, and provide an aesthetic identity for the waterfront. Where possible, native plants should be selected for river and stream renaturation. Trees that can tolerate a high water table, provide strong shade, enhance habitat value for wildlife, and provide good cover for roving animals, should be used for riparian corridors (DEP 2006). The selection should fit soil profiles and hydrology in different zones. 76 77 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land is Depending on project design, river Maintenance costs for river widening required in riparian urban areas. and stream renaturation costs may include clearing weeds/vegetation; include protection or conservation removing obstructions, dirt, and Land on which river and stream of land adjacent to watercourses; silt; and repairing riverbanks. These renaturation is conducted may be removal of impervious surfaces maintenance activities can be public or private. and barriers (e.g., concrete); and conducted manually or mechanically. revegetation of land adjacent to the Land required in riparian areas may watercourse. overlap with multiple landowners where renaturation work is required on longer lengths along a waterway, and may increase transaction costs associated with engagement of numerous landowners and stakeholders. Example land-related costs: • Acquisition costs • Land use (e.g., payments to landowners) costs • Land protection costs, including managing and controlling access UNIT COST EXAMPLES THROUGHOUT THE GLOBE • Removal of riverbed or bank fixation from • Restoration of natural watercourse from European European cost data: US$1.80–US$1,426/m of cost data: US$18–US$1,188/m of river stretch restored watercourse (Ayres et al. 2014). recovered (Ayres et al. 2014). • Nature-based “Soft Bank” protection and water • Manual maintenance activity costs: US$5,730– buffering (e.g., brush mattresses, revegetation, US$51,311/km of river per year (Aerts 2018). geotextiles); costs reflect smaller rural river • Mechanical maintenance activity costs: US$1,680– branches in Europe: US$54,000–US$978,000/ US$17,096/km of river per year (Aerts 2018). km (Ayres et al. 2014). Thailand Photo by James Zwadlo on Unsplash 78 79 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned in river and stream renaturation, drawn from selected case studies around the globe. Project #1: Bishan–Ang Mo Kio Park, 2009–12 Project #3: Cheonggyecheon, 2002–05 Location: Singapore Location: Seoul, South Korea Description: Bishan–-Ang Mo Kio Park was designed as an Description: The Seoul Metropolitan Government dismantled a ambitious water management and park project, with a focus 10-lane roadway and the 4-lane elevated highway that carried over on recreation and social interaction. It is one of the largest and 170,000 vehicles daily, and daylighted the ancient Cheonggyecheon most successful parks in Southeast Asia. To realize the park, an Stream to create a major arterial public space in 2005. The old concrete canal was stripped of concrete and naturalized into transformed street encourages the use of public transit, and offers a a 3-kilometer long meandering river with open lawns and gently new environmentally sustainable, pedestrian-oriented green corridor. sloping grassy banks on both sides. The park offers many amenities, The project contributed to a 15.1% increase in bus ridership and picnic areas, walkways, and cycle routes. It also includes allotment a 3.3% increase in subway ridership between 2003 and 2008. The gardens where residents can rent and raise planter beds. A revitalized street attracts 64,000 visitors daily. The daylighting of designated butterfly habitat area, and other areas with emphasis the river brought immense social value to the city and its residents. on biodiversity complement active recreation areas. Twenty-one new bridges were constructed to extend public amenities for the pedestrians and connect adjacent neighborhoods to each Photo by Jimmy Tan on Flickr Benefits Photo by Brian Kusler on Flickr other and the recreational spaces in the middle. Social, Health, Heat Stress and Flood Risk Reduction. Benefits Source Tourism, Health and Wellbeing, Heat Stress and Flood Risk Ramboll Studio Dreiseitl Reduction. https://www.asla.org/2016awards/169669.html Source Paradigm shift Long-term initiative Residents Innovative Sustainable Public engagement Seoul Metropolitan Government for traditional to transform changed view and governance and pedestrian- with residents, local https://globaldesigningcities.org/publication/global-street-design- flood country’s water ownership toward interagency oriented public merchants, and guide/streets/special-conditions/elevated-structure-removal/case- infrastructure bodies the river park coordination space entrepreneurs study-cheonggyecheon-seoul-korea/ Project #2: Saw Mill River Daylighting Project, 2001–12 Project #4: Restoration of Small Water Bodies (SWBR), 2009–12 Location: Yonkers, NY, USA Location: Beijing, China Description: The Saw Mill River in Yonkers was kept underground Description: In 2012, Beijing implemented a 30–50 km2 restoration in the 1920s after the industry together with residents had turned of Small Water Bodies to improve flood control and the ecology it into a polluted sewer. It remained buried until 2001 when the of the river, the riparian zones, and the floodplain. Instead of Groundwork Hudson Valley—an environmental NGO focused resorting to the traditional practice of building dams, the project on improving the physical and social environment of urban team chose to enlarge the space of the river. The project improved communities—began to investigate a possibility of recovering hydromorphological conditions, the longitudinal and lateral the river and securing funding for the project. The Saw Mill River continuity, and the green areas on both sides of the river. The Coalition established the project, and conducted the initial research restoration created additional environmental, recreational, and and public outreach. As a result of these community efforts, a scenic value for the communities. Guidelines to assess the biological section of the river, previously hidden by a large parking lot, was and hydromorphological status of rivers were developed, along daylighted and naturalized. The project was so successful that more with plans to introduce them as standards for the city. sections of the Saw Mill River in Yonkers are now being daylighted. Photo by Google Earth Yonkers demonstrates that daylighting can be good for the Photo by Scott Meltzer Benefits environment, community, economy, and the municipal budget. Biodiversity, Health, Heat Stress and Flood Risk Reduction. Source Benefits Beijing Park and Forest Department of International Cooperation Recreation, Biodiversity, Social and Urban Revitalization. https://www.sciencedirect.com/science/article/pii/ Source S209563391500009X Environmental Grant funded, The project Saw Mill River Coalition, Groundwork Hudson Valley. Restoration and Guidelines Raising the organizations which provided sparked for rehabilitation to assess city sensibility for https://www.americanrivers.org/wp-content/uploads/2016/05/ initiated the opportunity to downtown approach standards for ecologically AmericanRivers_daylighting-streams-report.pdf process by public leverage other revitalization other restoration oriented actions discussion funding sources project projects by villagers 80 81 REFERENCES Aerts, J.C. 2018. A review of cost estimates for flood adaptation. Water, 10(11)1646. Ayres, A., Gerdes, H., Goeller, B., Lago, M., Catalinas, M., García Cantón, Á., Brouwer, R., Sheremet, O., Vermaat, J., Angelopoulos, N. and Cowx, I. 2014. Inventory Of River Restoration Measures: Effects, Costs And Benefits. REstoring rivers for effective catchment management (REFORM) Buckley R.C., and Brough, P. 2017. Economic Value of Parks via Human Mental Health: An Analytical Framework. Front. Ecol. Evol. https://doi.org/10.3389/fevo.2017.00016 Department of Environmental Protection, Pennsylvania. 2006. Stormwater Best Management Practices Manual. https://pecpa.org/wp-content/uploads/Stormwater-BMP-Manual.pdf D’Haese, S., Cardon, G., and Deforche, B. 2015. The environment and physical activity. In M. Frelut (Ed.) The ECOG’s eBook on child and adolescent obesity. Brussels, Belgium: European Childhood Obesity Group (ECOG). Eisenberg, B. and Polcher, V. 2020. Nature-Based Solutions Technical Handbook. UNaLab Horizon. https://unalab.eu/ system/files/2020-02/unalab-technical-handbook-nature-based-solutions2020-02-17.pdf Hathway, E.A. and Sharples, S., 2012. The interaction of rivers and urban form in mitigating the Urban Heat Island effect: A UK case study. Building and Environment, 58, 14-22. Helliwell, J.F., Huang, H., Wang, S. and Norton, M. 2020. Statistical Appendix for Chapter 2 of World Happiness Report 2020. New York: Sustainable Development Solutions Network. Natural Water Retention Measures(NWRM). Natural Bank Stabilisation. http://nwrm.eu/sites/default/files/nwrm_ ressources/n10_-_natural_bank_stabilisation.pdf Ozment, Suzanne; Ellison,Gretchen; Jongman,Brenden. 2019. Nature Based Solutions for Disaster Risk Management. Washington, D.C. : World Bank Group. http://documents.worldbank.org/curated/en/253401551126252092/Booklet Soar, P.J. and Thorne, C.R. 2001. Channel restoration design for meandering rivers. Engineer Research and Development Center, Coastal and Hydraulics Lab. Vicksburg, MS, USA. 2030 palette. 2020. Riparian Buffers. http://2030palette.org/riparian-buffers/ Veról, A.P., Bigate Lourenço, I., Fraga, J.P.R., Battemarco, B.P., Merlo, M.L., Canedo de Magalhães, P. and Miguez, M.G. 2020. River Restoration Integrated with Sustainable Urban Water Management for Resilient Cities. Sustainability, 12(11) 4677. Strassbourg, France Photo by Reiseuhu on Unsplash 82 83 FACTS AND FIGURES DESCRIPTION Interest in nature-based solutions in buildings has increased considerably in the recent years. These solutions include adding green surfaces to building roofs and facades, creating opportunities to capture, store, and reuse stormwater, improve air quality, and reduce temperatures. They provide urban flooding and heat reduction benefits, and at the same time they can reduce costs by enhancing efficiency of climate control systems in buildings. Green roofs and facades may also improve property values and marketability of a building, especially in urban areas with little green space, and accommodate additional space for human use and urban functions associated with food production. Materials and technologies that support and monitor the growth of mosses, sedums, herbs, and low-growing grasses—common choices for green roofs—are entering the market. Research and innovation increasingly focus on the potential of productive rooftop gardens that also provide food, educational, recreational, and biodiversity benefits. Growing evidence on the safety and efficiency of building solutions and their ability to increase the R–value—a measure of the resistance of a material to the heat flow—of the roofing system, is promoting new applications that can result in energy cost savings and reduce the urban heat island effect, greenhouse gas emissions and the carbon footprint of the building. TYPE OF CITY SCALE APPROACH Neighborhood Create Construction of new green roofs and green facades on new buildings or existing Coastal Delta buildings (renovation). City River basin River Mountain PROCESSES Evapotranspiration Biodiversity Infiltration Outdoor cooling Shade Indoor cooling BUILDING SOLUTIONS Water Water storage collection and reuse Singapore Photo by Chuttersnap on Unsplash 84 85 VISUALIZATIONS VISUALIZATION OF BUILDING SOLUTIONS IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR GREEN ROOFS AND GREEN FACADES Extensive green roofs Extensive green roofs consist of several horizontal layers—bioengineered growth medium; membranes to support and control plant roots; buffers to collect, filter, store, reuse, or discharge water, as well as structural and 3 insulation layers. Performance criteria based on desired plant typology and the quantity of water determine the thickness and the composition of the layered structure. The roofs are normally not accessible to the public and have drought resistant plants that can withstand variations in temperature and sun exposure (Eisenberg and Polcher 2020). 1 Intensive green roofs The structure of intensive green roofs has a thicker substrate layer supporting higher variety of vegetation. In addition to water management and cooling, they provide amenities to building residents—opportunities for gardening, 2 exercise, sunbathing, relaxation, and socializing. Intensive green roofs have good returns on investment of lowering building energy bills. They provide habitats for attractive species, birds, bees, and other pollinators. Installation and maintenance come with a higher price tag than extensive green roofs (Eisenberg and Polcher 2020). Rooftop gardens are a special type of intensive green roofs, which serve as a productive garden for urban farming. Rooftop gardens require higher investments and a robust structural capacity of the roof to support the higher installation and, maintenance, but offer higher use and accessibility to people. A special type of smart green roofs is constructed with a system of crates located under the vegetation layer that stores rainwater. The crate system can be dynamically controlled and drained at a later preferred time. In return, the stored rainwater can be used for irrigation (Dakdoctors. com). Details of increased benefits for the urban living environment Ground-based green facades Ground-based green facades are a type of green wall with climbing plants rooted in ground planters. The climbing or self-clinging plants, with adhesive pads as part of their anatomy, can grow directly on the wall or on a special frame connected to the wall. The plants extract water and nutrients from soil 1 2 3 at ground level and can grow very tall, and adjust to climate fluctuations and different lighting conditions. Many flowering and evergreen species can add aesthetic experience to exterior walls, cool, and freshen the air (Eisenberg and Polcher 2020). Facade-bounded greening Facade-bounded greening is a type of green wall using technology for irrigation and special substrates for reducing the weight of green facades (Eisenberg Application of nature-based A green roof serves as communal Rooftop gardens offer additional and Polcher 2020). They are more expensive than ground-based greening and solutions at the scale of buildings space that brings neighbors and usable space in dense urban require higher use of resources in construction and maintenance. Facade- signals the urgency of urban coworkers together, enriches social environments; provide bounded greening allows for a combination of 10–15 plant species, most adaptation to climate change, and interaction, and increases community opportunities to grow flowers and often mosses and perennials, and grows fast and uniform. The thin layer of soil enhances the built identity. trust. vegetables, exercise, work, and inhibits their suitability in cold, temperate regions (Iwaszuk et al. 2019). rest. 86 87 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of building solutions. The diagram in this section shows a sampling of important benefits that building solutions can provide to people. Water quality and sediment management Pluvial flood risk reduction Social interaction Pluvial flood regulation Heat stress risk reduction Resources production Biodiversity Drought Heat regulation regulation BUILDING SOLUTIONS Education Air pollution regulation Biodiversity Human health Pluvial flood risk reduction: Green roofs effectively capture, Also, rooftop agricultural entrepreneurship can create Pluvial flood regulation: Green roofs capture and store rainwater in the soil and in the roof construction and thus, reduce peak store, and recycle rainwater, reducing the amount of water much needed low skill and part-time jobs, and engage local stormwater load on stormwater and sewerage systems. Standards capacities range depending on the type of green roof (see section running off to impervious surfaces and ending up in the sewer communities on cooperative production (Bade et al. 2011). Special Techniques), varying from 20–50 l/m² for extensive green roofs to 30–160 l/m² for intensive green roofs (Eisenberg and system during a storm. Most cities have combined sewer and Human health: Urban green has a positive environmental and Polcher 2020). stormwater systems designed with lower capacity than required psychological affect. Green walls provide cooling and shade. today. As a result, sewers and stormwater management systems Green roofs can be used for exercise, gardening, and social Heat regulation: The vegetation layer of a green roof and a green facade absorbs solar radiation through photosynthesis; protects are easily overwhelmed, streets and properties get flooded, interaction—all positive factors in public health (Gehrels et al. the heat transmission into the building; and provides shade if trees are planted. It reduces building temperature and cools the and significant amounts of untreated discharge end up in 2016). surrounding air (Gehrels et al. 2016). Several studies demonstrate that green roof temperatures can be 16–22°C (60.8–71.6°F) rivers. Widespread application of green roofs can reduce the Education: Roof gardens are important sources of information lower than that of conventional roofs (EPA n.d.). When transforming 80–90% of the roofs in a city to green roofs, they may reduce damage from pluvial floods, protect property, and reduce the about the environment. They can serve as classrooms for the average ambient temperature between 0.3°C and 3°C (32.5°F and 37.4° F) (Santamoursi 2014). Research conducted in Lagos , pollution—and water treatment costs—of surface water and in local schools, an observation and testing ground for students Nigeria, showed that a green facade reduces internal air temperatures by an average of 2.3°C (36.14°F) (Akinwolemiswa et al. 2018), urban rivers (Hop and Hiemstra 2012). interested in nature, biology, and the environment (Hop and and reduces the temperature of the facade itself between 2°C and 10°C (35.6°F and 50°F) compared to the natural stone (Eisenberg Heat stress risk reduction: Sufficiently irrigated, green roofs and Hiemstra 2012; Sheweka and Magdy 2011). and Polcher 2020). facades have a strong cooling effect on their surroundings. They Biodiversity: Green roofs and green walls enhance urban improve air quality; intercept, absorb and reflect solar radiation, biodiversity. They provide food and shelter for different species, Other functions: Green roofs and green facades mitigate the loss of urban biodiversity, reduce air pollution, and can reduce drought reducing the amount of solar radiation reaching the wall surface; and safe hiding and nesting places. Up to a certain height, roofs impacts by promoting the reuse of water stored in roofs (Eisenberg and Polcher 2020). reduce the thermal load on buildings and the requirement for attract pollinator species and can become productive areas for air conditioning (Hop and Hiemstra 2012). Decreased ambient flowers, honey, herbs, and specialty products, local pollen, fruit, temperatures and reduced use of air conditioning help mitigate and berries (Cañero and Redondo 2010). urban heat island effect being even slightly more effective at Social interaction: Green roofs are great places for communities cooling the city at night (Bowler et al. 2010). Reducing extreme to meet and can become attractive places for intergenerational heat in cities brings a variety of socioeconomic benefits, activities, social interaction, and collaboration (Marissing 2008). including reduced mortality (Tan et al. 2010), improved health, Water quality and sediment management: The layered reduced energy cost and CO2 emissions (Roxon et al. 2020), and structure of most green roofs and facades facilitates sediment improved productivity of labor (Wong et al. 2017). capture and water filtration. As a result, stormwater processed Resource production: Like any form of local agriculture, by green roofs and walls is relatively clean and can be safely rooftop food production increases food supply. Rooftops can reused in many applications (Hop and Hiemstra 2012), reducing accommodate small agricultural businesses and reduce the the demand for treated water. distance food must travel from the producer to the consumer. 88 89 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: Green building solutions heavily depend on the ability of vegetation to survive, Accessibility: Roof access must be provided during the installation for the delivery of materials, and for succeed, and deliver benefits. In temperate climatic conditions, the capacity of green roofs and facades regular maintenance of the roofs (DDOE 2013). Public access to intensive roofs must be properly monitored to manage urban stormwater are based primarily on the quality of the installation, availability of right with the right set of safety measures put in place. kinds of substrate soils, membranes, and crates. In arid or semi-arid climates, drought-resistant plants need care and freshwater irrigation. In arid climates, economic viability of building solutions will be more challenging as a result of high irrigation costs (Akhter et al. 2018). Dimensions: • Green roofs: A study shows that the entire contributing drainage area to a green roof, including the green roof itself, must be no more than 25% larger than the area of the green roof (DDOE 2013). TECHNICAL • Green facades: A facade or wall of almost any size can be used to create a green wall; a minimum amount of space is required on the ground for planting and to remain healthy (Iwaszuk et al. 2019). Roof type: Green roofs can be installed on most roof surfaces. Certain roof materials, such as exposed chemically treated wood and uncoated galvanized metal, may not be appropriate for green roof tops URBAN due to potential pollutants leaching from these materials in the wet conditions and contaminating the planting substrate (Clark et al. 2010). Roof slope: A green roof water storage volume is at its maximum on a relatively flat roof (1% or 2%). Land use: Suitable land uses for green roofs and facades are a variety of buildings—residential, public, However, some inclination is needed to promote drainage and prevent ponding and saturation. A slope commercial, and office buildings, convention centers, and major utility structures. of up to 7% is most efficient for rainwater retention. Green roofs can be installed on rooftops with slopes up to 30% if structural interventions like baffles, grids, or strips are used to hold the growing medium that is the substrate on which the vegetation grows, often a mixture containing organic matter (DDOE 2013). Urban density: Green building solutions can be applied at any density from low to high. Substrate: • Green roofs: A recommended composition of the growing media for green roofs, provided in a study (DDOE 2013), is 80% lightweight material, no more than 20% of organic matter—normally well-aged compost. Media used in a green roof should have a maximum moisture capacity between 30% and 40% (DEP 2006). The thickness of the layer depends on the type of roof, ranging from 5–15 cm for Area: Small to medium. Green roofs and facades are applied at the building scale. intensive roofs to 15–48 cm for extensive roofs. Tree planting requires extra depths of the substrate (Eisenberg and Polcher 2020). • Green facades: Regular planting soil is the common choice in basic ground-based facades, although more complex green facades with weight restrictions must consider the use of light soils similar to green roofs. Integrated urban planning: Green building solutions can be an integral component of the roof and facade renovation or part of new building construction. Structural capacity of the roof: The structural capacity of existing roofs must be considered to support the weight of a green roof and the additional volume of water. • Extensive green roofs: 20 kg/m² to 190 kg/m². MAINTENANCE • Intensive roofs and rooftop gardens: 190 kg/m² to 680 kg/m² (Eisenberg and Polcher 2020). Green roofs: Green roofs require semi-annual inspections to ensure water outlets are clear of (dead and living) plants and debris. Extensive green roofs require minimal maintenance while an intensive green roof requires regular garden maintenance Facade orientation: All facade surfaces are potentially usable. The choice of plants should directly including pruning, cleaning and removal of debris, soil amendment, and nourishment. correspond to the amount of sunlight they will receive throughout the day depending on the façade orientation. (Eisenberg and Polcher 2020). Green facades: Ground-based facades require inspections during the first months after installation to ensure plant growth and direction. Subsequently annual inspection can be sufficient (Iwaszuk et al. 2019). 90 91 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land The cost of green roof installation Maintenance costs on green roofs or is required, potentially through varies widely depending on the types facades will be a function of the type collaboration and engagement of building solutions, the complexity of roof as well as of the local climate with building owners. of the installation roof, and material and weather. Frequent inspection of and labor costs at the site location. green roofs and facades is necessary to conduct necessary maintenance, such as clearing dead plants, weeding, pruning, and fertilizing. Intensive green roofs are generally more expensive than extensive green roofs. UNIT COST EXAMPLES THROUGHOUT THE GLOBE Construction and implementation Example green roof costs: Example green facade costs: • Extensive green roofs: US$60–US$270/m² • Ground-based façade: US$35–US$55/m² (US$60,000–US$2,700,000/ha) (Iwaszuk et al. (US$350,000–US$550,000/ha) (Perini and 2019). Rosasco 2013). • Intensive green roofs: > US$180/m² • Façade-bounded: US$480–US$1450/m² (US$1,800,000/ha) (Iwaszuk et al. 2019). (US$,800,000–$14,500,000/ha) (Perini and • Extensive green roofs cost roughly US$6–US$8 Rosasco 2013). per square foot less than semi-intensive green roofs. Smaller green roofs cost more per square foot than larger green roofs. Extensive green roofs cost US$10.30–US$12.50 more per square foot than a black roof; semi-intensive green roofs cost US$16.20–US$19.70 more per square foot than black roofs (U.S. GSA 2011). Maintenance Example green roof costs: Example green facade costs: • Extensive green roofs: US$0.60–US$3.50/m²/ • Green facades require annual pruning year (US$6,000–US$35,000/ha) (Iwaszuk et al. estimated at US$3.40/m2 (US$34,000/ha) 2019). and long-term cladding renovation estimated • Intensive green roofs: US$4.20–US$18.00/ at US$1,480/m2 (US$14,800,000/ha) (Perini m²/year (US$42,000–US$180,000/ha/year) and Rosasco 2013). (Iwaszuk et al. 2019). Nashville, TN, USA Photo by Khara Woods on Unsplash 92 93 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned in building solutions, drawn from the growing practice of integrating NBS in building solutions around the globe. Project #1: Greening Cairo’s roofs, 2001–03 Project #3: Bicentenario Park, 2007–16 Location: Cairo, Egypt Location: Bogotá, Colombia Description: The objective of the Cairo and Alexandria Green Roof Description: Bicentenario Park was conceived as a revitalization program was to offer low-income suburban families a possibility project in downtown Bogotá and inaugurated in 2016. It is a of growing their own food and to create income-generating reinforced concrete bridge that adapts to the topography of the opportunities. The program was wholeheartedly embraced by local terrain and meets a vast number of urban technicisms and norms of women, who began to produce fresh vegetables and use the roofs the city. In order to transform this bridge into a green public space for social gatherings in a safe, semiprivate setting. FAO initially of 4,600 m2, a series of extensive and intensive green roofs were trained 48 families in the use of hydroponics systems and green designed, resulting in eight small vegetated squares. A wide variety techniques, eliminating use of pesticides. Since then the project has of native and adapted plants were selected by the Botanical Garden become an urban and peri-urban horticulture model. of Bogotá. The new Parque Bicentenario restoration has become a healing factor in the division between the south and north sectors Benefits of Bogotá. Environmental, Climate, Micro-economy, Gender Empowerment. Photo by Doaa211 on Wikimedia Commons Source Photo by Alejandro Arango / El Equipo Mazzanti Benefits FAO Regional Office for Near East and North Africa Heat Stress Reduction, Equity, Recreation, Social Interaction. https://www.researchgate.net/publication/269873380_Green_ Source Roofs_in_Cairo_A_Holistic_Approach_for_Healthy_Productive_ Bogotá city, El Equipo Mazzanti Cities https://www.greenroofs.com/projects/parque-bicentenario-bogota/ Government Scope for Women Integrated Scope for equity, Design oriented: initiative in education and empowerment with park and publicness, social Launched as https://www.archdaily.co/co/898371/parque-bicentenario-un- collaboration with promotion of and knowledge neighborhood connection, and idea proyecto-que-ayuda-a-coser-una-herida-urbana-en-bogota local stakeholders healthy lifestyle transmission renewal plan crime reduction competition Project #2: Farming Kindergarten, 2013–15 Project #4: Building community-driven vertical greening systems for Location: Biên Hòa, Dong Nai, Vietnam people living on less than £1 a day: a case study in Nigeria (VGS), Description: Architects in 2013 conceived a new kindergarten 2014–16 building as a continuous productive green roof supplying fresh Location: Lagos, Nigeria produce, providing a food-growing experience to children. The Description: Low-income residents of Lagos installed an building is located next to a shoe factory and serves about 500 interior vertical greening system (VGS) prototype to grow children of the factory workers. The contemporary design of the produce, herbs and cool the immediate environment. VGS is a kindergarten provides a large playground and an innovative compact, affordable, low-tech passive technology. Yet, even in combination of developmentally important activities: growing food this challenging environment it can be effective and popular. and hands-on learning. The kindergarten projects aim to preserve a Community engagement surveys showed that VGSs reduce internal better understanding of the natural processes, and to make it more air temperature by an average of 2.3°C (36.14°F). Many users fun for early learners to spend time outdoors. pointed out the benefits of being able to grow medicinal plants, such as bitter leaves to treat diabetes, plants to treat malaria, as Benefits well as pumpkin leaves for general consumption. With the right Photo by OKI Hiroyuki Health, Education. Photo by Oluwafeyikemi H. Akinwolemiwa and Clarice Bleil de Souza kind of community entrepreneurship, VGSs can evolve into a Source viable commercial product and become a source of income for the Vo Trong Nghia Architects community. https://www.archdaily.com/566580/farming-kindergarten-vo- trong-nghia-architects Benefits Health, Education, Economy. Icon and showcase Learning Money saving Community Participatory Knowledge for new eco- experience and showcase https://worldarchitecture.org/architecture-projects/hfnfc/farming- involvement process between development Source building typology for children for building kidergarten-project-pages.html and local communities for future Oluwafeyikemi H. Akinwolemiwa for educational about agriculture energy empowerment and knowledge application https://www.sciencedirect.com/science/article/pii/ centers and nature efficiency institutions S0360132318300349 94 95 REFERENCES Akinwolemiwa, O., Bleil de Souza, C., De Luca, L. M., Gwilliam, J. 2018. Building community-driven vertical greening Tonietto, R., Fant, J., Ascher, J., Ellis, K., and Larkin, D. 2011. A comparison of bee communities of Chicago green roofs, systems for people living on less than £1 a day: a case study in Nigeria. Building and Environment 131, 227-287. parks and prairies. Landscape and Urban Planning, 103(1)102–08. (10.1016/j.buildenv.2018.01.022). US Department of the Environment. Stormwater Management Guidebook. Watershed Protection Division. District of Akther, M., He, J., Chu, A., Huang, J., and Van Duin, B. 2018. A review of green roof applications for managing urban Columbia. stormwater in different climatic zones. Sustainability, 10(8): 2864. https://doee.dc.gov/sites/default/files/dc/sites/ddoe/page_content/attachments/FinalGuidebook_changes%20 accepted_Chapters%201-7_07_29_2013_compressed.pdf Bade, T., Smid, G., Tonneijck, F. 2011. Groen loont! De groene stad, Apeldoorn. (Dutch). Bowler, D.E., Buyung-Ali, L., Knight, T.M., and Pullin, A.S. 2010. Urban greening to cool towns and cities: A systematic re- US Environmental Protection Agency. Using Green Roofs to Reduce Heat Islands. https://www.epa.gov/heatislands/using- view of the empirical evidence. Landscape and Urban Planning, 97(3) 147–55. green-roofs-reduce-heat-islands Clark, S.E., Long, B.V., Siu, C., Spicher, J., and Steele, K.A. 2008. Runoff Quality from Roofing during Early Life. Proceedings U.S. General Services Administration (USGSA). 2011. The Benefits and Challenges of Green Roofs on Public and of the Water Environment Federation, 2008 (16) 1048–62. Commercial Buildings. May 2011. https://www.gsa.gov/cdnstatic/The_Benefits_and_Challenges_of_Green_Roofs_on_Public_and_Commercial_Buildings. Dakdokters. Water collection on roofs. Online article. pdf https://dakdokters.nl/en/polder-roofs/ Dept. of Environmental Protection. 2006. Stormwater Best Management Practices (BMP) Manual. Pennsylvania. https://pecpa.org/wp-content/uploads/Stormwater-BMP-Manual.pdf Eisenberg, B. and Polcher, V. 2020. Nature-Based Solutions Technical Handbook. UNaLab Horizon. https://unalab.eu/ system/files/2020-02/unalab-technical-handbook-nature-based-solutions2020-02-17.pdf Fernández Cañero, R. and González Redondo, P., 2010. Green roofs as a habitat for birds: a review. Journal of Animal and Veterinary Advances, 9 (15) 2041–52. Gehrels, H., van der Meulen, S., Schasfoort, F., Bosch, P., Brolsma, R., van Dinther, D., Geerling, G.J., Goossens, M., Jacobs, C.M.J., Kok, S., and Massop, H.T.L. 2016. Designing green and blue infrastructure to support healthy urban living. TO2 federatie. https://openresearch.amsterdam/en/page/67880/designing-green-and-blue-infrastructure-to-support-healthy-urban Hop, M.E.C.M. and Hiemstra, J.A. 2012, July. Contribution of green roofs and green walls to ecosystem services of urban green. In: II International Symposium on Woody Ornamentals of the Temperate Zone 990:475–480. Iwaszuk, E., Rudik, G., Duin, L., Mederake, L., Davis, M., Naumann, S., and Wagner, I. 2019. Addressing Climate Change in Cities. Catalogue of Urban Nature-Based Solutions. Ecologic Institute, the Sendzimir Foundation: Berlin, Krakow. https://www.ecologic.eu/sites/default/files/publication/2020/addressing-climate-change-in-cities-nbs_catalogue.pdf Marissing, E. 2008. Buurten bij beleidsmakers, Faculteit Geowetenschappen en Koninklijk Nederlands Aardrijkskundig Genootschap. Universiteit Utrecht, Utrecht. (Dutch) Perini, K. and Rosasco, P. 2013. Cost–benefit analysis for green façades and living wall systems. Building and Environment, 70:110–121. Roxon, J., F.-J.Ulm, and R.J.-M.Pellenq. 2020. Urban heat island impact on state residential energy cost and CO2 emissions in the United States. Urban Climate, 31: 100546. https://www.sciencedirect.com/science/article/abs/pii/ S2212095518303560 Santamouris, M. 2014. Cooling the cities–a review of reflective and green roof mitigation technologies to fight heat island and improve comfort in urban environments. Solar energy, 103: 682–703. Sheweka, S. and Magdy, A.N. 2011. The living walls as an approach for a healthy urban environment. Energy Procedia, 6:592–99. Tan, J., Zheng, Y., Tang, X., Changyi Guo, C., Li, L., Song, G., Zhen, X., Yuan, D., Kalkstein, A.J., Li, F., and Chen, H. 2010. The urban heat island and its impact on heat waves and human health in Shanghai. Int J Biometeorol, 54:75–84. https://doi. org/10.1007/s00484-009-0256-x 96 97 FACTS AND FIGURES DESCRIPTION The successful protection, creation, and development of open green spaces is one of the key elements required to achieve sustainable urban development. Parks, unpaved, and biologically active green areas of every size can help cities adapt to climate change by cooling and enhancing the quality of air, providing shade, and offsetting the urban heat island effect. Unpaved areas can also absorb and attenuate the velocity of stormwater, reduce the amount of water entering the sewerage system, and minimize stormwater and sewage discharge, contributing to urban flood risk management. These values can be enhanced through targeted interventions to improve infiltration, reduce runoff, and increase water retention. However, they must be designed with clear performance objectives and also resonate with users to encourage a sense of collective ownership and stewardship. Accessible open green spaces of all scales are highly valuable to quality of life and public health benefits for urban communities as they attract social and physical activity. Whereas many open green spaces can provide habitat for species, some parks also serve as critical refugia for biodiversity in an otherwise highly transformed urban context. Green spaces vary significantly in spatial extent and properties, and may include both private and public lands. They range from gardens in neighborhoods to large city parks connected to the surrounding landscape. Such a variation in their characteristics also means that they provide a broad spectrum of social and environmental values. TYPE OF CITY SCALE APPROACH Protect Neighborhood Protect existing open green spaces. Coastal Delta Rehabilitate, Restore, Enhance City Upgrade or renovation existing green spaces. Allow temporal use of undefined areas as green River basin spaces. River Mountain Create Construct new open green spaces. PROCESSES Carbon sequestration Evapotranspiration Cooling effect Water storage Shade Biodiversity OPEN GREEN SPACES Infiltration Lima, Peru Photo by Dan Gold on Unsplash 98 99 VISUALIZATIONS VISUALIZATION OF OPEN GREEN SPACES IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR OPEN GREEN SPACES Pocket parks Pocket parks are relatively small open spaces distributed throughout the urban fabric. Pocket parks serve the immediate population of a neighborhood and provide a wide variety of small- 3 scale recreation possibilities, such as playgrounds, dog parks, workout stations, water fountains, vegetable and flower planters, and other props for neighborhood recreation. Pocket parks can also appear on vacant lots through community initiative. 2 1 Natural playgrounds Playgrounds with trees, flowers, rocks, and water features help children develop development skills, such as sensory, tactile perceptions, creativity, and appreciation for nature (Kahn and Kellert 2002). Playgrounds encourage social and physical activity for all ages. Ponds and other blue–green infrastructure in playgrounds can provide educational opportunities to children, green retreats of recreation, and enjoyment to others, while contributing to Details of increased benefits for the stormwater management. urban living environment 1 2 3 Climate-proof residential gardens Residential gardens can have a large cumulative impact in stormwater reduction if they are integrated into larger green infrastructure networks. Each garden manages stormwater from buildings, roofs, and courtyards, capturing and recycling stormwater. The vegetation also helps mitigate heat, while trees, Open green spaces provide refugia In tropical and subtropical regions, Accessible green spaces of all scales bushes, and other vegetation provide habitat. Residents can also for wildlife, recreational and green spaces offer areas for cooling, close to residential and commercial use gardens for growing vegetables and recreational uses (see also cultural programs, and amenities making it safer and more pleasant to areas are highly valuable to quality of Urban Farming). for urban communities. spend time outdoors. life and public health benefits. 100 101 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of open green spaces. The diagram in this section shows a sampling of important benefits that open green spaces can provide to people. Pluvial flood risk Social interaction reduction Pluvial flood regulation Heat stress risk reduction Subsidence regulation Biodiversity OPEN GREEN Heat SPACES Air pollution regulation regulation Tourism and recreation Water pollution regulation Biodiversity Carbon storage and Human health sequestration Drought regulation Stimulate local economies and job creation Pluvial flood regulation: Open green spaces help manage stormwater and mitigate floods. Trees, gardens, and lawns intercept and Pluvial flood risk reduction: Open green spaces reduce the Stimulate local economies and job creation: Parks and open absorb rainwater through soil infiltration and evapotranspiration, also helping to recharge aquifers. The capacity of green spaces to impact of storms and can decrease potential damage to green spaces enhance the reputation of a city and attract reduce flooding depends on the extent of the park relative to the catchment area, the topography, type and density of vegetation, buildings and infrastructure. To achieve a greater cumulative tourism. Parks can also host cultural events, becoming an asset. and soil characteristics. Lakes, ponds and other water detention zones in parks can add (temporary) water storage capacities to the effect, a series of green open spaces should be planned as a They may increase property values and tax revenue (Dunnett et system and thereby reduce stormwater peak flows. coherent blue–green infrastructure network that can absorb, al. 2002; Wendel 2011). infiltrate, and store large volumes of stormwater and reduce the Human health: Urban green spaces have a positive effect on Heat regulation: Urban green spaces reduce heat by providing shade and evaporative cooling (Gehrels et al. 2016). By some velocity of stormwater flow in large parts of the city. (Gehrels et mental wellbeing and physical health. The mitigation of pollution estimates, large park areas of more than 10 hectares can reduce temperatures by 1°C or 2°C (33.8 or 35.6°F) within 350 meters of al. 2016). and urban heat island effect leads to fewer respiratory problems the park boundary (Aram et al. 2019). Small parks can maintain air temperatures lower than the surrounding built areas by as much Heat stress risk reduction: Urban green spaces reduce heat and reduces the number of lethal outcomes of heat exposure as 3°C (37.4°F) (Singerland 2012). stress by providing shade and evaporative cooling (Gehrels et among the elderly. Lower temperatures in urban green spaces al. 2016). Green spaces and urban planting help keep thermal allow people to exercise during hot days, and increase physical Other functions: Open green spaces reduce subsidence, build resistance against drought, remove pollutants from air, water, and comfort and reduce the incidence of heat-related illnesses wellbeing of people. Parks can improve mental health and soil, and support biodiversity by providing nourishment and habitat for flora and fauna (Eisenberg and Polcher 2020). (Howe and Boden 2007); increase productivity (Seppanen et reduce stress levels, and offer getaways from the crowds of a al.2004); and reduce the accumulation of heat inside buildings. city (Kaplan and Kaplan 1982). Tourism and recreation: Green open spaces attract social Biodiversity: Open spaces can serve to protect critical remnant and physical activity (Wan and Shen 2015). They bring people habitat. Urban greenery is essential to the survival of many together for relaxation, recreational activities, and sports species and preservation of biodiversity. These benefits can be (Halprin 1981; Wendel et al. 2012). Parks increase the prestige, strengthened by proactively integrating key biodiversity areas economic success, and the livability of a city (Woolley 2003). in the open space network of a city. For optimal environmental Carbon storage and sequestration: Open green spaces and performance, this requires a comprehensive network of green urban parks store carbon in soil and vegetation, mitigating climate patches and corridors that provides food and habitat for biota change. An example from a region with a temperate climate and facilitates its movement across the landscape (De la Barrerra indicates that carbon density in an urban park is approximately et al. 2016; Dunnett et al. 2002). 130 tons of CO2 per ha, of which approximately 75% is stored Social interaction: Parks and green open spaces give distinct below ground (Linden et al. 2020). The contribution of open identity to a neighborhood or a city, giving residents a shared green spaces and urban parks to carbon sequestration will vary sense of belonging to a larger and more complex social context significantly based on the habitat structure and growth rates of (Yilmaz and Mumcu 2016). This sense of community has been plants associated with the corridor. Where dominated by grassy proven beneficial to the individual physical and mental wellbeing areas, rates are likely to be in the region of 0.5 to 5 tons of CO2 and has a strong set of public health as well as economic benefits per ha per year whereas this could increase to well above 5 tons (Bertram and Rehdanz 2015). of CO2 per ha per year for forest-dominated corridors. 102 103 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: Open green spaces are valuable in every climate zone. Their contribution to Social involvement: The identity of a park should resonate with its users and respond to their cultural stormwater management will be the greatest in geographical regions with frequent heavy precipitation. preferences and needs while delivering on its environmental performance. When the performative Their ability to provide shade and reduce temperatures is most valuable in dry, hot areas. In dry climates, aspects of the parks are made visible and understandable, users will value its ecosystem services and play establishing and sustaining open green spaces throughout the year requires greater care to avoid lowering an important role in protecting the park (City of Gold Coast 2018). the water tables, reducing soil recharge rates, and to ensure sufficient water is available for plant survival. Soil: Soils and plants should be chosen simultaneously to enhance performance for stormwater URBAN management. Soils should have a relatively dense structure with a good infiltration capacity and depth to sustain plant growth. Loose soils are at risk of being eroded, but solid, clay soils will not absorb enough water, and could accelerate stormwater runoff. The right combination of soils will allow water to percolate but will retain the nutrients necessary for plant growth. Clay soils or areas with high groundwater levels require open water bodies to contribute to stormwater management (Gehrels et al. 2016). Land use: Suitable land uses for green open spaces are parks, gardens, squares, streets, outdoor sports facilities, and vacant lots that can receive greenery. TECHNICAL Planting and growing strategy: The choice of planting in an open green space site depends on climate Urban density: Suitable urban density for open green spaces ranges from low to high. and lighting conditions, the size, its soils, and available water resources. Preference should be given to resilient native species. In addition, other factors for choosing the plants include climate mitigation potential, water management and phytoremediation capacities, aesthetic value, and contribution to urban wildlife habitat. Area: Small to large. Open green spaces are nature-based solutions that can be designed for application at a neighborhood, district, or city scale. Dimensions: Parks of any size provide multiple cultural and recreational benefits. The urban context, availability of land, and its performative criteria for resilience objectives—such as urban flooding, heat, or biodiversity—will determine the area of a park (City of Gold Coast 2018): • Small local and pocket parks range from 250–4,000 m2 and serve the immediate neighborhood Integrated urban planning: Green open spaces can be integrated into several urban programs— within a 400-meter radius or 5-minute walking distance. They can provide limited recreational environmental conservation, parks, green infrastructure, new developments and regeneration; and vacant opportunities and accommodate short visits. lot reclamation. • Medium size district parks range from 2–4 hectares and can serve several neighborhoods within a 400–800-meter distance. These often support a wider variety of informal recreational uses and include community facilities. • Large city parks of 10–20 hectares cater the recreational needs of the residents within a 1–5 km MAINTENANCE radius as well as visitors and tourists. City parks can attract people from across the city and the region. An open green space is an important public asset that is aimed to serve all members of society without financial profit. The Inclusivity: The design or upgrading of public parks and open green spaces should follow the principles return of investment can come from climate mitigation and public health benefits. Maintenance of parks and open spaces of universal design that facilitate physical accessibility for people of every age and of all levels of physical should be planned for, funded, and systematically performed. Local stewardship and volunteer support can help with the ability (City of Gold Coast 2018). To secure equitable access, communities of different social and ethnic upkeep, but maintenance can be systematically ensured by city taxes financing and creating job opportunities for local low- backgrounds should be able to engage in cultural practices and enjoy the benefits of nature and fresh air skill employment. equally. Vandalism and crime prevention: The work on open green spaces should follow well-tested design guidelines for vandalism and crime prevention. Environmental urban design elements offer opportunities to prevent vandalism and crime. Planting, pathway and spatial arrangement of built elements, lighting, and way-finding graphics should promote visibility and passive surveillance. In crime-prone areas, tree canopies can be trimmed to allow maximum crossview, and time restrictions may be imposed on park use (City of Gold Coast 2018). 104 105 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land is Urban open green space costs are a Maintenance costs for urban open required for open green space in function of labor, site preparation, green spaces vary depending on open urban areas. design, and construction costs. space design, use, type of vegetation, Costs associated with managing and local climatic conditions. Land on which open green space may and controlling access may also be be located may be public or private. included. Land required for open green space may be relatively large in scale— though urban open green spaces vary widely in size—and may result in transaction costs associated with landowners and other stakeholder engagement. Example land-related costs: • Acquisition costs • Land use (e.g., payments to landowners) costs • Land protection costs, including managing and controlling access • Community resettlement costs UNIT COST EXAMPLES THROUGHOUT THE GLOBE A study of European parks provided the following • Estimates of maintenance costs in the United estimates for capital costs: Kingdom vary between US$0.4–$2/m2/year • High-cost intensive use urban parks: > US$270/ (US$4,000–US$20,000/ha/year) (Tempesta 2015). m2 (US$2,700,000/ha). • Medium cost urban parks: US$135–US$270/m2 (US$1,350,000–US$2,700,000/ha). • Low-cost parks: US$68–US$270/m2 (US$680,000–US$2,700,000/ha). • Very low-cost parks: < US$68/m2 (US$680,000/ ha) (Holden 2007). Rio de Janeiro, Brazil Photo by Karl Groendal on Unsplash 106 107 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned in creating open green spaces from international experiences. Project #1: Julio Mario Santo Domingo Library Park, Completed Project #3: Kibera Public Space Project, 2006 to date 2010 Location: Lindi Village, Nairobi, Kenya Location: Bogotá, Colombia Description: Located at a busy river crossing, the project was Description: The Santo Domingo Library and gardens, set in 55,000 previously subject to periodic destructive floods, and lacked basic m2 space, offer extraordinary benefits to the population of the sanitation and amenities to youth. The Kibera Public Space project, northern districts of Bogotá—Usaquen and Suba. The restoration designed by KDI with local residents in 2006, developed programs in 2010 involved conserving many existing plants while adding new that would meet some of the physical, social, and economic needs ones. The gardens create an excellent education space and contain of its residents, and provide activities for the youth. The result was many rediscovered indigenous plants that are endangered, reviving a network of productive public spaces, with various hubs of cultural a process of ecological restoration. The project demonstrates how exchange, economic activity, and environmental remediation. important a healthy, green space can be to the mental wellbeing Today, resident-managed programs, many led by women and and physical health of urban dwellers youth, maintain these sites, help residents build new skills, and generate income. The network continues to expand and improve Benefits environmental and social resilience across the settlement. Photo by Saúl Ortega on Flickr Education, Biodiversity, Health. Photo by Ninara on Flickr Source Benefits Diana Wiesner and Daniel Bermúdez. Education, Gender Empowerment. http://landezine.com/index.php/2013/06/julio-mario-santo- Source domingo-library-park-by-diana-wiesner-arquitectura-y-paisaje/ Kounkuey Design Initiative (KDI) Private donation Equity Linked to cultural Gender and Comprehensive Community https://www.kounkuey.org/projects/kibera_public_space_project_ from local promotion amenities, offering https://www.researchgate.net/publication/307751026_Julio_ youth task of involvement in network stakeholders through playing interdisciplinary Mario_Santodomingo_Library's_Public_Space empowerment neighborhood project management and learning activities recovery and expansion Project #2: Chulalongkorn Centenary Park, 2012–17 Project #4: Common-Unity, Completed 2016 Location: Bangkok, Thailand Location: San Pablo Xalpa, Azcapotzalco, Mexico City Description: The Chulalongkorn Centenary Park in Bangkok is the Description: Common-Unity is a public space rehabilitation project first critical piece of green infrastructure for the city, designed to for San Pablo Xalpa Housing Unit in Azcapotzalco, Mexico City. The mitigate detrimental ecological issues. It has added a much-needed unit was previously divided into sectors. Walls, fences, and barriers outdoor public space to the gray city in 2017. Its green roof is the led to a fragmentation of spaces that did not allow the community largest in the country, and the park's filtration system treats water to benefit from public spaces. The project transformed such a from neighboring areas. It has become a showcase for ecological divided space into a neighborhood space. The recovered public and social impacts of landscape architecture in dense urban areas. space became an extension of each apartment. The strategy was Its site area spans 48,000 m2 and is 1.3 kilometers in length, and it a big success: people contributed to the design and an increasing sits in the campus area of Chulalongkorn University. number of people decided to remove their fences Benefits Benefits Pollutants Reduction, Biodiversity, Tourism, Social Interaction. Heat Stress Risk Reduction, Social Interaction, Health and wellbeing. Photo by BunBn on Wikimedia Commons Source Photo by Google Earth Source LandProcess, Kotchakorn Voraakhom Rozana Montiel, Estudio de Arquitectura www.nparks.gov.sg/-/media/cuge/ebook/citygreen/cg16/cg16_05. https://www.archdaily.com/892388/common-unity-rozana-montiel- pdf estudio-de-arquitectura https://worldlandscapearchitect.com/chulalongkorn-centenary- Urban Design oriented: Integrated in Renewal of Community Active space green and Launched as an educational park-green-infrastructure-for-the-city-of-bangkok/#.YWV7s_lBxPY common involvement in between natural international idea and cultural residential areas project design private icon competition institution and building trust and execution and public through design properties 108 109 REFERENCES Aram, F., García, E.H., Solgi, E. and Mansournia, S., 2019. Urban green space cooling effect in cities. Heliyon, 5(4): e01339. Bertram, C. and Rehdanz, K., 2015. The role of urban green space for human well-being. Ecological Economics, 120:139– 52. De la Barrera, F., Reyes-Paecke, S. and Banzhaf, E. 2016. Indicators for green spaces in contrasting urban settings. Ecological Indicators, 62: 212–219. Dunnett, N., Swanwick, C. and Woolley, H. 2002. Improving urban parks, play areas and green spaces. London: Department for transport, local government and the regions. Eisenberg, B. and Polcher, V. 2020. Nature-Based Solutions Technical Handbook. UNaLab Horizon. https://unalab.eu/system/files/2020-02/unalab-technical-handbook-nature-based-solutions2020-02-17.pdf European Commission. 2020b, April. Nature-based Solutions for climate mitigation (No. 978-92-76-18200–9). Publications Office of the European Union. https://doi.org/10.2777/458136 Gehrels, H., van der Meulen, S., Schasfoort, F., Bosch, P., Brolsma, R., van Dinther, D., Geerling, G.J., Goossens, M., Jacobs, C.M.J., Kok, S. and Massop, H.T.L. 2016. Designing Green And Blue Infrastructure To Support Healthy Urban Living. TO2 federatie. http://www.adaptivecircularcities.com/wp-content/uploads/2016/07/T02-ACC-WP3-Green-Blue- infrastructure-for-Healthy-Urban-Living-Final-report-160701.pdf Halprin, L. 1981. Sketchbooks of Lawrence Halprin. Process Architecture. Holden, R. 2007. Costs of large city parks and open spaces: Olympics Park Benchmarking S5E005. https://www.academia.edu/7288676/Costs_of_large_city_parks_and_open_spaces Howe, A.S. and Boden, B.P., 2007. Heat-related illness in athletes. The American Journal of Sports Medicine, 35(8), 1384- 1395. Kahn Jr, P.H. and Kellert, S.R. eds., 2002. Children and nature: Psychological, sociocultural, and evolutionary investigations. MITpress. Kaplan, S. and Kaplan, R. 1982. Cognition and Environment: Functioning in An Uncertain World. Sixth edition. 287. Preager. New York. Lindén, L., Riikonen, A., Setälä, H., and Yli-Pelkonen., V. 2020. Quantifying carbon stocks in urban parks under cold climate conditions. Urban Forestry & Urban Greening, 49:126633. https://doi.org/10.1016/j.ufug.2020.126633 Park Design Guidelines. City of Gold Coast, Australia. https://ws-07-8bdxkw.goldcoast.qld.gov.au/documents/bf/park-design-guidelines.pdf Seppanen, O., Fisk, W.J. and Faulkner, D. 2004. Control of temperature for health and productivity in offices. Slingerland, J.D. 2012. Mitigation of the urban heat island effect by using water and vegetation. Delft University of Technology. Tempesta, T. 2015. Benefits and costs of urban parks: A review. Aestimum, 127–43. Wan, C. and Shen, G.Q. 2015. Salient attributes of urban green spaces in high density cities: The case of Hong Kong. Habitat International, 49:92–99. Wendel, H.E.W., Zarger, R.K. and Mihelcic, J.R. 2012. Accessibility and usability: Green space preferences, perceptions, and barriers in a rapidly urbanizing city in Latin America. Landscape and Urban Planning, 107(3) 272–82. Woolley, H. 2003. Urban Open Spaces. 208. Spon Press. London. Wendel, H.E.W. 2011. An examination of the impacts of urbanization on green space access and water resources: a developed and developing world perspective. University of South Florida. Yilmaz, S. and Mumcu, S. 2016. Urban green areas and design principles. Environmental Sustainability and Landscape Management, 100. Dnipropetrovsk, Ukraine Photo by Artiom Vallat on Unsplash 110 111 FACTS AND FIGURES DESCRIPTION Green corridors, also known as linear natural infrastructure, are an essential part of the urban landscape ecology. These strips of trees, plants, or vegetation can be found at a range of scales, and typically connect green spaces in a city, creating a green urban infrastructure network. Green corridors complement green spaces in a city, protect natural habitat, and typically contain the most valuable animal species urban habitat. The corridors allow biota to move, survive, and propagate. Highly fragmented urban landscapes, where distances between green spaces are large and corridors are insufficient or absent, reduce the landscape’s potential to mitigate flood risks through enhanced interception and infiltration. In many cities, the ratio of paved to biologically active surfaces that can absorb, store, and recirculate water is out of balance, and the stormwater drainage and sewer system cannot handle the growing amounts of precipitation. As a result, damaging floods and river pollution can occur. Cities can mitigate this problem by establishing more green corridors and connecting them into a green urban infrastructure network, which would lessen the load on the drainage and sewerage systems, and ultimately protect the urban living environment from flooding and polluted water discharges. With growing awareness of the importance of green corridors, cities are being proactive in designing interconnected green spaces, with both large scale as well as smaller scale interventions in neighborhoods and buildings. Riparian corridors can often be found as prominent corridors in cities. They act as important dispersal corridors for climate-induced species and they provide microclimatic refugia from warming (Krosby et al. 2018). Smaller scale interventions include green streets, green avenues, and gardens, providing microcorridors and stepping stones that better support biodiversity values and ecosystem services. TYPE OF CITY SCALE APPROACH Protect Neighborhood Preserve natural corridors, particularly drainage lines. Coastal Delta Preserve the existing tree structure. City Rehabilitate, Restore, Enhance Integrate existing elements of green River basin infrastructure into a connected system. River Mountain Upgrade of individual elements. Create Expand the existing tree structure and the connective green structure of the city. PROCESSES Carbon sequestration Cooling effect Evapotranspiration Air cleaning Shade Biodiversity GREEN CORRIDORS Infiltration Jakarta, Indonesia Photo by Fawazlul Rizqi on Unsplash 112 113 VISUALIZATIONS VISUALIZATION OF GREEN CORRIDORS IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR GREEN CORRIDORS Street tree canopies Streets with large tree canopies enhance the image of a city, increase its competitiveness, deliver economic and environmental benefits. Some cities are famous for a particular type of tree and 3 attract seasonal tourism based on the tree-blooming schedule. 2 Tree canopies circulate rainwater, create local microclimate, absorb pollution, provide shade, and attenuate heat. Heat reduction translates into lower cooling bills for buildings. Cooler streets with large tree canopies promote walking and social interaction and generate more retail and hospitality revenue. 1 Green avenues Green avenues and boulevards are among the most attractive urban typologies, historically proven to improve business, increase property taxes and enhance the prestige and desirability of cities. Functioning as environmental corridors from the start, they are instrumental in climate adaptation. An unpaved, vegetated medium can be integrated into the green infrastructure network for climate adaptation and help prevent floods. Continuous tree canopy efficiently mitigates urban heat, provides shade and shelter for small Details of increased benefits for the species, and promotes walking. urban living environment 1 2 3 Urban green corridors The most efficient way to create a green corridor is to plant deciduous trees as large canopies. Trees can be placed along the streets, open train tracks, and other transportation and infrastructure corridors, in open and derelict spaces. Green corridors should be designed for multiple functions such as new bike paths, walking, and jogging routes, in addition to water management areas. Green corridors Maintaining buffers along drainage Stepping stones for biodiversity are Maintaining green verges and can help establish better landscape connectivity across the city and lines improves water quality and provided when the design of parks establishing trees alongside roadways improve ecosystem functions (NWC 2016). provides critical habitat linkages and gardens seek to complement enhance aesthetics, reduces heat, and for wildlife. existing corridors. provides shade for pedestrians. 114 115 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of green corridors. The diagram in this section shows a sampling of important benefits that green corridors can provide to people. Pluvial flood risk reduction Pluvial flood Heat stress regulation risk reduction Cultural Biodiversity GREEN Air pollution Heat CORRIDORS regulation regulation Tourism and recreation Water pollution regulation Biodiversity Carbon storage and sequestration Human health Pluvial flood regulation: As part of a green space network in a city, green corridors can help manage stormwater and mitigate floods Heat stress risk reduction: Trees in green corridors reduce and found an average sequestration rate of 0.5 ± 0.3 tons CO2 through interception of rainwater, evapotranspiration, root water uptake, and soil infiltration (Gehrels et al. 2016). The integration of temperatures in urban areas by creating shade and through per ha per year (Bernal et al. 2018). green corridors as part of road drainage and streetscapes can also serve to promote infiltration and decelerate flows, while a range evapotranspiration. They reduce the amount of heat reflected Human health: Tree canopies reduce peak temperatures and of opportunities exist to integrate them into existing drainage networks. Their effective reach then expands from purely natural off the buildings and pavement (2030 Palette 2020). The quality make street life more tolerable on hot summer days (Gehrels elements to being part of the existing gray infrastructure network of a city. of tree canopy, its size, density, leaf color, and the distance et al. 2016). The shade reduces the amount of harmful UV between the trees determine its effectiveness. A continuous radiation reaching pedestrians; it reduces wind speeds and air Heat regulation: The potential for green corridors to regulate heat depends largely on the height and density of tree canopies tree corridor will have a greater cumulative heat mitigation pollution. Green corridors work as buffers and shield people present within the corridor. A tree canopy reduces the temperature in the shade by 1–5°C (33.8–41°F) compared to an open area, effect than a set of individual trees (DDOE 2012). from the noise and pollution of large-scale infrastructure. They and by 11–17°C (51.8–62.8°F) compared to a parking lot. A 10% increase in the tree canopy cover reduces the maximum midday Pluvial flood risk reduction: Trees in green corridors increase invite people to participate in year-round sports and physical air temperature by about 1°C (33.8°F) (2030 Palette 2020). The cooling efficiency of trees depends on the foliage color, density, the interception of rainwater in urban environments, reducing activities, encourage biking, and complement public parks in thickness, and texture. Darker and denser greenery provides shade and reduces temperatures more effectively (Lin and Lin 2010). risks of local floods and peak loads of stormwater in the their ability to reduce stress and promote a sense of wellbeing. sewerage system. Pedestrians experience better thermal comfort and find the Other functions: Green corridors improve water and air quality, reduce noise, and offset the loss of biodiversity in urban environments Tourism and recreation: Green corridors are important for heat more bearable (Gehrels et al. 2016). The presence of tree (Eisenberg and Polcher 2018). recreation and attracting tourists to a city. Greenery makes canopies within walking distance from residential buildings, can summer tourism in hot climates more pleasant because of reduce mortality in elderly individuals (Takano et al. 2002). their ability to reduce temperatures in the city. Green corridors Biodiversity: The spatial arrangement of street trees and green promote alternative mobility and safe recreation, provide corridors define levels of biodiversity in cities. Green corridors different ways of experiencing the city, and attract people to the sustain biodiversity by connecting different patches of green outdoors (Sullivan et al. 2004). within the city and to the larger habitats in the region. In smaller Carbon storage and sequestration: Linear green corridors, habitats, they facilitate movement of biota between different such as street trees store and sequester carbon. For example, patches and natural colonization of new areas. Landscape an empirical study of Beijing street trees found very high connectivity is vital for biodiversity. Street trees provide habitat heterogeneity carbon density rates between different corridors for birds, squirrels, and smaller species. They are also stepping (Tang et al. 2016). This study estimated the average aboveground stones that allow species to jump from one relatively safe area carbon density of urban street trees at 13.9 ± 0.7 tons CO2 per to another until they reach a larger and safer landscape habitat ha. The contribution of green corridors to carbon sequestration patch (Vollaard et al. 2018). will vary significantly based on the habitat structure and growth Cultural: Together with architecture, street trees and green rates of plants associated with the corridor. Where dominated corridors enhance urban identity and raise the prestige of by grassy areas, rates are likely to be in the region of 0.5 to 5 different areas. Several cities celebrate trees by organizing tons CO2 per ha per year whereas this could increase to well festivals and other cultural events around their blooming above 5 tons CO2 per ha per year for forest-dominated corridors; schedule (Yilmaz and Mumcu 2016). 116 117 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: Plants for green corridors should be selected according to the hardiness zone, Infrastructure restrictions: A clearance must be established to protect the green corridors from built soil type, sunlight and rain data, frost schedules, and other factors that affect the success of trees and infrastructure, and to ensure that trees are not interfering with roads, train tracks, gas mains, and other vegetation. Local data can be gathered to check what trees have done well in the area, what plant diseases elements of urban infrastructure (Eisenberg and Polcher 2018). Tree species must be durable and able to have occurred, and what weather changes are most pronounced. In semi-arid and arid climates, special withstand ground vibration, air and water pollution, and other aggravations of urban conditions. The trees considerations regarding water needs, irrigation, and the impacts of establishing green corridors on water must be periodically trimmed to preserve the right distance from infrastructure for the long term. tables and soil recharge rates should be evaluated prior to implementation. Hydrology: Matching new urban trees and plants with the right soils should strike a delicate balance. URBAN They should get proper irrigation for their growth, but they should not be water logged if inundated by a flood. The soils should be layered to provide proper drainage, yet retain nutrients. For urban tree propagation, many climate-appropriate technologies introduce structural elements, filters, membranes, and irrigation mechanisms to secure growth and health of urban trees. Given the costs and vulnerability of urban trees, it is important to make use of these technologies (Eisenberg and Polcher 2018). Land use: Infrastructure networks, residential streets, and major infrastructure including rail tracks and highways are suitable land uses for linear green corridors. Soil: Soils in urban areas are frequently compacted, nutrient deficient, have high levels of acidity or alkalinity, and may be contaminated by salt and other ice-melting compounds, or be polluted by industrial or other human activity. Local soil tests are therefore typically required to inform any soil augmentation necessary to support selected vegetation and fulfill their pH value, drainage, and structural requirements Urban density: Suitable urban density for linear green corridors ranges from low to high. (Forest Research n.d.). TECHNICAL Area: Small to large. Linear green corridors are nature-based solutions suitable for application at neighborhood, district, and city scale. Slope: Planting methods for green corridors with slopes steeper than 3:1 involve creating a level planting space on the slope. A terrace can be dug into the slope in the shape of a step (DDOE 2012). Integrated urban planning: Linear green corridors can be planted as part of street improvement programs, transformation of underused infrastructure and open spaces, and as part of new urban development. Species selection: When developing green corridors, plant species should be selected that support and enhance important benefits. This may range from tree selection to optimize carbon sequestration and heat reduction benefits to the selection of plant species that add to aesthetic values or which provide habitat or food for important wildlife. MAINTENANCE Dimensions: Urban trees along linear infrastructure, such as roads, require an appropriately sized three- dimensional space to establish their roots securely. A tree pit and a grate must keep an appropriate Maintenance requirements vary considerably across habitats and should be carefully considered when planning new green amount of unpaved surface around the tree to allow water to percolate; and to the extent possible, keep corridors. Irrigation requirements vary considerably depending on plant types, the soils, and prevailing climatic conditions. debris and pollutants out of the tree pit. The depth of the roots, the height, and the size of the canopy Young trees typically require regular watering until the root structure is firmly established (Gilman 1994). In high traffic must be considered (DDOE 2012), along with the distance between the trees. Root space should ideally areas, trees should be trimmed to at least 2.5–3 meters from the ground so as not to interfere with the passage of cars and be 12 m3 with a minimum depth of 1.5 meters (Eisenberg and Polcher 2018) although this is not always pedestrians. Trees that produce too much fruit, nuts, or leaf litter should not be planted along streetscapes unless included achievable in an urban context. The space between the edge of the tree pit and the street curb or a in street maintenance budgets. Formative pruning is usually not needed for newly planted trees but may be beneficial for building should be least 1.8 meters to allow more space for the roots (DDOE 2012). the tree structure. Utility restrictions: Trees in green corridors can interfere with the street level and underground utilities. In areas with overhead power lines, trees should be selected to maintain an acceptable distance between the top of the trees and the wires. Appropriate clearance must also be established and preserved between the underground utility lines and the tree roots (Gilman 1994). 118 119 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land Costs associated with protecting, Maintenance of green corridors is required for green corridor restoring, or creating urban green depend on the type and size of trees development. corridors will depend on the size of or vegetation, the complexity of the green corridor, site conditions, planting, local climatic conditions, Land on which green corridors may the type and size of trees and other and labor costs. be located may be public or private. vegetation required to be planted, and underlying labor and material Land area required for green costs. corridors will vary from smaller to larger areas, raising transaction costs if engagement and collaboration with multiple landowners and stakeholders is necessary Example land-related costs: • Acquisition costs • Land use (e.g., payments to landowners) costs • Land protection costs, including managing and controlling access • Community resettlement costs UNIT COST EXAMPLES THROUGHOUT THE GLOBE • Installation costs for street trees cost between • Maintenance costs for street trees range from US$6,680–US$11,666 over a 50-year time US$547–US$2,252 per tree over a 50-year time period, depending on the method of delivery and period, including inspection, leaf clearing, and installation, watering, anchoring, the aeration pruning (GBU 2019). system, and the tree grille (GBU 2019). Ho Chi Minh City, Vietnam Photo by Tron Le on Unsplash 120 121 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned about green corridors, drawn from the growing popularity of NBS throughout the globe. Project #1: The Green Belt of Vitoria-Gasteiz, 1990s to 2008 Project #3: Cuernavaca Ferrocarril Linear Park, 2016–20 Location: Vitoria-Gasteiz, Spain (Phase 1) Description: The Green Belt is a group of peri-urban parks Location: Mexico City, Mexico of high ecological and landscape value, strategically linked Description: Located at the heart of Mexico City, the project by ecorecreational corridors. It is a result of an ambitious consists of an active urban forest of 4.5 km in length, which environmental restoration project initiated in the early 1990s crosses 22 districts and buildings. This green corridor is an active, around the outlying areas of Vitoria-Gasteiz with the objective of programmed, and sustainable connector of spaces. It created creating a large, green area for recreational use around the city. spaces that contribute to the spirit of community and it has It offers many different environments with a wealth of natural promoted a sense of ownership of public space by people. It also features. Woods, rivers, wetlands, meadows, fields, groves, and achieves high social value by strengthening identity and memory of hedgerows are some of the varied ecosystems that coexist. Some of the history of the place, by creating a sustainable and high quality these ecosystems, such as the restored wetlands of Salburuaor and environment for people to linger and use at their own leisure. the River Zadorra ecosystem, have won recognition at international level for their high environmental value. Benefits Photo by Alberto Cabello on Flickr Photo by Google Earth Education, Culture, Biodiversity, Health, Community. Benefits Source Health, Equity, Environmental Sustainability. Gaeta Springall Architects Source https://mooool.com/en/linear-park-ferrocarril-de-cuernavaca-by- Vitoria-Gasteiz Municipal Council gaeta-springall-arquitectos.html Sustainable International Long time https://www.researchgate.net/publication/259121417_The_Green_ Showcase for Design oriented: Active stewardship recognition and restoration Belt_of_Vitoria-Gasteiz_A_successful_practice_for_sustainable_ coexistence of Launched as an participatory and urban city icon strategy of urban_planning infrastructure and international idea process with development peri-urban areas social interaction competition neighbors Project #2: Liuyun Xiaoqu District Project, 2000–10 Project #4: The Rail Corridor Project, 2015–21 Location: Hangzhou, China Location: Singapore Description: Changes in land ownership schemes in Liuyun Description: The closure of Keratapi Tanah Melayu (KTM) railway Xiaoqu district allowed for a redevelopment of public space and in 2011, bisecting Singapore released 24 km of continuous land the creation of the first green corridors for pedestrians, within spanning the entire nation. In the face of population growth and densely populated urban blocks. Initially, owners of the ground- urbanization, Singapore made the bold decision to transform the floor apartments were able to make a living by converting their 100-hectare site into public space to provide benefit to its people premises to commercial uses—at first for local shops and later for and the environment. designer clothes retail and cafes. The ground floor conversions The design included the creation of 8 themed stretches and 10 occurred in waves, eventually converting nearly all the ground activity nodes, dedicated to different sports or leisure activities. floors to commercial use, turning the area into an open, mixed- The project reinvented hidden space within Singapore to inspire use neighborhood. With much of the area now being used for movement and new ways of experiencing the environment. It allows commercial purposes, its narrow pedestrian passages were opened people to enjoy the interactions between city, nature, land, water, to public access. The municipality then improved utilities and community and art, as well as enjoy heritage sites. The Rail Corridor Photo by Karl Fjellstrom / Far East Mobility infrastructure, pedestrian areas, and key landscaping features Photo by Thomas Timlen on Flickr has become a green, vibrant and healthy space to engage residents including tree maintenance and replanting, that created shaded and visitors with Singapore's natural and built heritage. public spaces. Benefits Benefits Education, Historic Value, Health and Sports, Heat Stress Risk Economy, Health and Wellbeing, Heat Stress Risk Reduction. Reduction. District renewal Priority of Boost economy Symbol for Long term vision, Launched as an strategy and pedestrian and real estate Source sustainable framework and international Source promotion of mobility value Far East Mobility, Hangzhou Municipality development of design strategies competition Tan See Nin, Urban Redevelopment Authority mixed-use urban and green https://www.fareast.mobi/en/bestpractices/liuyun public space to guide for masterplan https://www.csc.gov.sg/articles/co-creating-the-rail-corridor's- program infrastructure progressive development future implementation 122 123 REFERENCES DDOE. Stormwater Management. Guidebook. 2012. District Department of the Environment. Watershed Protection Division. District of Columbia. Washington D.C. https://nacto.org/docs/usdg/stormwater_management_guide_district_ columbia.pdf Eisenberg, B., and Polcher, V. 2018. Nature Based Solutions–Technical Handbook. UNaLab project, European Union. https://unalab.eu/system/files/2020-02/unalab-technical-handbook-nature-based-solutions2020-02-17.pdf European Commission. 2020b, April. Nature-based Solutions for climate mitigation (No. 978-92-76-18200–9). Publications Office of the European Union. https://doi.org/10.2777/458136 Forest Research. n.d. Urban Tree Manual. https://www.forestresearch.gov.uk/tools-and-resources/urban-tree-manual/ Gehrels, H., van der Meulen, S., Schasfoort, F., Bosch, P., Brolsma, R., van Dinther, D., Geerling, G.J., Goossens, M., Jacobs, C.M.J., Kok, S. and Massop, H.T.L. 2016. Designing green and blue infrastructure to support healthy urban living. TO2 federatie. http://www.adaptivecircularcities.com/wp-content/uploads/2016/07/T02-ACC-WP3-Green-Blue- infrastructure-for-Healthy-Urban-Living-Final-report-160701.pdf Gerrits, A.M.J. 2010. The role of interception in the hydrological cycle. VSSD. GreenBlue Urban (GBU). 2019. Street Tree Cost Benefit Analysis. https://www.treeconomics.co.uk/wp-content/uploads/2018/08/GBU_Street-Tree-Cost-Benefit-Analysis-2018.pdf Gilman, E.F., Knox, G.W., Neal, C.A. and Yadav, U. 1994. Microirrigation affects growth and root distribution of trees in fabric containers. Hort Technology, 4(1)43–45. Lin, B.S. and Lin, Y.J., 2010. Cooling effect of shade trees with different characteristics in a subtropical urban park. Hort Science, 45(1)83–86. Natural Walking Cities (NWC). 2019. Creating and promoting walkable and natural infrastructure for sustainable cities. http://naturalwalkingcities.com/ Sullivan, W.C., Kuo, F.E. and Depooter, S.F. 2004. The fruit of urban nature: Vital neighborhood spaces. Environment and Behavior, 36(5)678–700. Takano, T., Nakamura, K. and Watanabe, M. 2002. Urban residential environments and senior citizens’ longevity in megacity areas: the importance of walkable green spaces. Journal of Epidemiology & Community Health, 56(12)913–18. Tang, Y., Chen, A., and Zhao, S. 2016. Carbon Storage and Sequestration of Urban Street Trees in Beijing, China. Front. Ecol. Evol. https://doi.org/10.3389/fevo.2016.00053 2030 palette. Habitat Corridors. 2020. http://2030palette. org/habitat-corridors/ Vollaard, P., Jacques Vink, J., and de Zwarte, N. Stad maken natuur/ Making urban nature. 2018. https://www.naturalcity.nl/ Yilmaz, S. and Mumcu, S. 2016. Urban green areas and design principles. Environmental Sustainability and Landscape Management, 100. George Town, Malaysia Photo by elCarito on Unsplash 124 125 FACTS AND FIGURES DESCRIPTION Urban farming is a way for people to grow crops for personal consumption or to sell locally and beyond. Urban agriculture can be defined as the growing of plants or animals within and around cities and associated activities such as producing and delivering inputs as well as processing and marketing of agricultural products (FAO 2011). The most important incentive for urban farming is to increase food security for urban livelihoods. In many parts of the world, it helps build resilient food systems. In addition to contributing to food security, urban farming provides multiple benefits. It supports climate change adaptation and mitigation, biodiversity and ecosystem services, sustainable agricultural, resource efficiency, urban regeneration, land management, public health, social cohesion, and economic growth (Artmann and Sartison 2018). Urban farming comprises a variety of activities—aquaculture, livestock, plants, and food production. Agro-ecosystems as well as forests, industrial rooftop gardens, residential and community gardens, containers on balconies, vacant land, edible landscaping, vertical edible green infrastructure, and marine and freshwater systems are suitable spaces for urban food products (Grewal et al. 2012; Haberman et al. 2014; Lovel 2010; Russo et al. 2017). As a result of rapid urban development peri-urban agriculture is under threat, but at the same time food demand in cities is increasing. To secure this, accomplishing sustainable agriculture is key. However, without proper management, urban farming could pollute the environment or create additional risks, and can come in direct conflict with real estate and infrastructure development pressures. It can also compete with valuable open space for conservation and place increasing pressure on remaining natural ecosystems. This means the economic contribution of urban farming, social equity, and the need to balance food production with conservation efforts need to be understood and integrated into policies and designs. When managed and planned well, urban farming as an NBS, can play an important role in sustainable urban development and help urban residents to reconnect with nature, reclaim public spaces, recover from disasters, and gain income (Artmann and Sartison 2018). TYPE OF CITY SCALE APPROACH Protect Neighborhood Protect prevalent urban farming practice and local food supply networks. Coastal Delta City Rehabilitate, Restore, Enhance Allow temporal use of unzoned areas for urban farming. River basin River Mountain Create Create new areas for urban farming. PROCESSES Cooling effect Carbon sequestration Evapotranspiration Water storage and reuse Biodiversity URBAN FARMING Infiltration Soil and water cleaning China Photo by ZHIDA LI on Unsplash 126 127 VISUALIZATIONS VISUALIZATION OF URBAN FARMING IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR URBAN FARMING Raised beds 2 Raised bed farming is a low-cost technique in urban areas where soil pollution can be a threat. Raised beds can be built to any size, using any noncorrosive material, as long as the structure provides 3 good drainage. Raised beds have many advantages: in temperate 1 regions with cold winters, the beds warm up quicker than the barren ground in the spring, thereby extending the growing season. In areas with limited sun, beds can be tilted to maximize the exposure for plant growth. In cold months beds can be covered or converted into greenhouses. Amphibious farming Inspired by the ancient Aztec way of farming called chinampas, amphibious farming uses artificial islands built in water. The islands are secured in place by driving wooden stakes into a lakebed and establishing a perimeter with woven reed fences. Amphibious farming areas create a grid, with large enough canals between the island crop beds for a small boat to move through. Planting beds use compost produced in situ as the growing medium. Details of increased benefits for the urban living environment 1 2 3 Floating farming Floating agriculture is a way of utilizing inundated areas for food production. The method creates buoyant beds filled with compost from decomposing vegetation, which becomes a growing substrate for crops. The beds float on the surface of the water, creating additional areas of land suitable for agriculture. Floating cultivation can be up to 10 times more productive than traditionally farmed Outdoor urban farming can Farming creates strong urban Farming can take place in vacant land but are not suitable in waterbodies that experience high flow produce local food; reduce identity and prevents soil erosion, lots, on rooftops, and high potential velocities (CTCN n.d.; Haq et al. 2004). urban waste stream by mudslides, and other hazardous agricultural land. It delivers multiple absorbing compost; and reduce effects of loose soils in areas with ecosystem service benefits, creates stormwater runoff by infiltrating complex terrains, while increasing local employment and a beneficial and storing water. social cohesion. sense of community belonging. 128 129 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of urban farming. The diagram in this section shows a sampling of important benefits that urban farming can provide to people. Pluvial flood risk reduction Social interaction Pluvial flood regulation Resources Landslide production regulation URBAN Heat FARMING regulation Drought regulation Education Air pollution regulation Biodiversity Carbon storage and sequestration Human health Soil pollution regulation Stimulate local economies and job creation Pluvial flood regulation: Outdoor urban farms increase the amount of pervious surface, and can capture, store, and infiltrate Pluvial flood risk reduction: Urban farming changes the ratio Stimulate local economies and job creation: Urban farming rainwater, reducing runoff (Aerts et al. 2016). Farming soils often have high levels of organic content and a structure that allows between paved and unpaved surface in the city reducing the can be an important part of local economies. An urban farm can water to percolate deeper into the ground. Adding more organic content can increase their water retention and storage capacity, amount of stormwater runoff that ends up in storm drains. become a source of additional nutrition from fresh produce, allowing the soils to act as natural sponges. Farms can also include ponds and rain collectors to store additional water. During heavy storms, that means protecting urban rivers from vegetables, and fruit and a decent source of protein from fish untreated runoff. Open-soil farming stores and infiltrates and other products of aquaculture. In some places farms Heat regulation: Urban agricultural areas, especially orchards, reduce urban heat by creating shade and have an ameliorating effect rainwater, as its rich organic soils act as sponges, soaking up can contribute to food security and create job opportunities on the immediate local climate, and in the case of arid climates, increased humidity (Smit et al. 1996). rainwater (Aerts et al. 2016). (Agbonlahor et al. 2007). Resources production: Provision of food, in particular vegetable Human health: Farming improves social wellbeing and nutritional Other functions: Urban farms clean air, water, and soil, and offset drought by storing water. In areas where development is not crops, fruit, spices, and poultry, is the primary benefit of urban health (Hallett et al. 2016) and has a wide range of physiological possible, such as steep slopes, floodplains, and areas with no bedrock and unstable soils, farming can be used to stabilize soils and farming (Aerts et al. 2016). and psychological benefits. prevent mudslides (Smit et al. 1996). Compost can be produced and collected locally, reducing waste (Olson and Gulliver 2011). Carbon storage and sequestration: The carbon sequestration Education: Urban agriculture creates a better understanding of Urban farms may increase biodiversity in the surrounding areas. potential of urban agriculture is largely dependent on the degree the value and the meaning of food, which provides opportunities to which trees are combined within the agricultural landscape. to educate children. Participation in farming helps children learn While removal potential varies considerably, average biomass and gain better understanding of the natural environment, while accumulation for agroforestry is estimated between those of adults can gain new skills, such as learning about nutritional planted forests and naturally regenerated forests (10.8–15.6 tons values of crops they grow (Smit 1996). CO2 per ha per year for the first 20 years of growth), which could Social interaction: Localized agriculture has a very high value be expected given agroforestry activities typically involve lower of social land use. Community initiatives in urban farming have planting densities. Removal factors after 20 years, however, are proven successful to empower social cohesion between different very low, with growth rates in the 20–60-year period below 0.1 generations and groups, as urban farming can build stronger tons CO2 per ha per year (Bernal et al. 2018). Empirical studies communities and create a spirit of cooperation. Such communal investigating the potential of urban agriculture found that food farming can foster social support networks that are proven to be grown in cities can reduce greenhouse gas emissions in different essential to human wellbeing. Consequently, urban farms create ways, for instance by reducing food mileage (Lee et al. 2015), better neighborhoods, with less crime and vandalism (Ober Allen growing vegetables in residential gardens (Cleveland et al. 2017) et al. 2008; Bradley and Galt 2014). Farms become community or using soilless crops (Llorach-Massana et al 2017). centers where also other social development strategies can be developed (Teig et al. 2009, Smit 1996). 130 131 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: Urban farming can be implemented in urban environments where climate is Accessibility: Generally, farmers need to access markets for trade and to sell their goods (Thapa and appropriate for outdoor agriculture. Warmer temperatures and elevated levels of carbon dioxide in urban Murayama 2008). Urban farms producing enough surplus typically benefit from proximity to markets. environments have the potential to extend the growing season and improve crop productivity (Hallet et This minimizes transportation costs, keeps produce in top condition, maximizes economic benefits for al. 2016; Wagstaff and Wortman 2015). In dry climates, urban farming considerations should include the the producer and delivers optimal nutritional content to the consumers (Thapa and Murayama 2008). evaluation of water requirements, with preferences identified for crops tolerant to arid conditions or In addition, areas for urban farming require easy accessibility to roads for transportation and logistics requiring limited water use. operations. Hydrology: Access to water is critical for urban farming. For individual low-income farmers, an irrigation system can be a major expense (Dumitrescu 2013). The use of potable water for irrigation is highly controversial, and in many places very costly. Rainwater is the best alternative, particularly if its quality URBAN can be monitored. Rainwater can be captured from precipitation and reused for irrigation when needed. Storage containers can be designed to purify the water too. Raised bed agriculture is a good way to optimize the quantity of water needed and create ideal moisture conditions for the crops. Alluvial plains often offered suitable moisture conditions and soils for urban agriculture. Land use: Urban farming often exploits unused resources in the city—wastewater, solid waste, vacant lots, bodies of water, slopes, and rooftops. It puts idle land to productive use, maintains the land in good Soil: Urban farming requires soil preparation to provide good conditions for plant growth. Soils must have condition and generates income from temporarily available land. It is also compatible with open space, the right mineral content, compacted soils must be tilled to improve aeration and drainage, and organic parks, sports, universities, roadsides, and floodplains (Smit et al. 1996). content must be augmented to provide fair nutrition to the plants and ensure water retention. Alluvial soils are highly suitable for agriculture. Sandy urban soils are unsuitable for agriculture production unless soil enrichment is performed. Urban density: Suitable urban density for urban farming ranges from low to medium. Contamination: Contamination is a major issue in urban farming. Soil, water, and air pollution in cities can affect crop production, and worker and consumer safety (Agrawal et al. 2003; Mapanda et al. 2005). Avoiding cultivation in these contexts is an option to mitigate the risk of contamination, especially in former industrial areas or nearby factories (Pandey and Pandey 2009), on lands irrigated with water, or on soil contaminated industrial or mining wastes (Mapanda et al. 2005). Area: Small to medium. Urban farming is a nature-based solution typically planned and designed for application at a neighborhood, district or city scale. TECHNICAL Integrated urban planning: Urban farming can be an integral component of the transformation of underused spaces, multifunctional green areas, and food programs. Dimensions: Small plots for urban farming generally range between 0.01–3 hectares (Zeunert and Waterman 2018; Kaufman and Bailkey 2000). Usually, farms smaller than 1 hectare are organized by individuals or small cooperatives; commercial farms generally require much more space. Production capacity is dependent on the type of crops and local conditions. Bed dimensions are based on how far a person, tending to the plants, can reach—so beds are usually about 1 to 1.2 meters wide by 2 to 2.5 meters long (Dumitrescu 2013). Crop type: Urban farming includes vegetable and fruit tree cultivation, as well as other specialized crops (e.g., medicinal and ornamentals), wood production, small-scale animal husbandry, beekeeping, and aquaculture consisting of combined fish and plant culture (Orsini et al. 2013). 132 133 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land is Costs of urban farming vary by Maintenance costs of urban farming required for urban farming. location, labor and land costs; include traditional farming activities whether land must be acquired over a growing season, including Land on which urban farms may be or secured for use to develop an weeding, fertilizing, watering, and located may be public or private. urban farm; and the extent of harvesting. site preparation needed, such as Land area required for urban enclosures or others. farms may range from small areas for community gardens to larger agricultural operations either within or adjacent to urban areas. Example land-related costs: • Acquisition costs • Land use (e.g., payments to landowners) costs • Land protection costs, including managing and controlling access. UNIT COST EXAMPLES THROUGHOUT THE GLOBE • Urban farming costs in the U.S. is estimated growing structures, and labor for one year. The at US$46.71/m2/year (US$467,100/ha/ cost does not include land acquisition or the costs year), including personnel, location plans, of remediation (USDA 2016). environmental assessment, site preparation, Addis Ababa, Ethiopia Photo by Eyoel Kahssay on Unsplash 134 135 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned in urban farming, drawn from the growing popularity of NBS throughout the globe. Project #1: Floating farms, ongoing Project #3: Kibera's vertical farms, 1980s to date Location: Xochimilco, Mexico City Location: Kibera, Nairobi, Kenya Description: Waterborne chinampa farming system—sometimes Description: Urban agriculture in Nairobi is practiced in backyard called floating gardens—is a form of ancient raised bed agriculture farms, on open spaces under power lines, along roadsides, railway that continues to be successfully used by small farmers today. lines and riverbanks as well as on institutional land. In the mid Chinampas are long and narrow floating garden beds separated 1980s, when the urban population reached one million mark, 20% by canals. The garden lot is built of layers of woven wetland reed of Nairobi households were growing crops and 17% kept livestock mats, stacked on top of each other while alternating directions within the city limits. It is estimated that 30% of households in of a weave, and interlaced with mud and thick mats of decaying Nairobi are involved in urban farming. Social value is created by vegetation. The layered bed accumulates additional highly fertile the promotion of value-chain development and direct producer– fluvial sediment and makes for an exceptionally productive growth consumer marketing. Family time and labor spent on urban medium. The benefit of a chinampa system is that the water in the agriculture depends on the size of land, intensity of the practice, canals provides a consistent passive source of irrigation that allows and number of livestock. In the peri-urban transition areas, most for efficient and reliable agricultural practice. labor for vegetable production is provided by women. Photo by Hernán García Crespo on Flickr Photo by Ninara on Flickr Benefits Benefits History and Identity, Education, Economy. Economy, Gender Empowerment, Education. Source Source Mexico City, FAO, Authority of the world natural and cultural African Studies Centre, Leiden, Netherlands Preservation of Local Boost of local heritage zone in Xochimilco, Tlahuac, and Milpa Alta Households Collaboration of Woman http://documents1.worldbank.org/ cultural knowledge community economies and https://www.fao.org/3/I9159EN/i9159en.pdf largely involved local community empowerment. curated/en/434431468331834592/ and agricultural empowerment tourism https://www.fao.org/giahs/giahsaroundtheworld/designated-sites/ in urban farming in research pdf/807590NWP0UDS00Box0379817B00PUBLIC0.pdf heritage latin-america-and-the-caribbean/chinampa-system-mexico/en/ surveys Project #2: Agricultural Sector Wide Approach (ASWAp) 2011–15 Project #4: Chacrita Productiva, 2011–14 Location: Lilongwe, Malawi Location: Lima, Peru Description: Medium-scale farms have become a major force Description: Lima’s population growth and economic development in Malawi’s agricultural sector. Malawi’s most recent official is driving unprecedented demand for a greater variety and higher agricultural survey indicates that urban farms account for over a quality of food. On a small scale, urban agriculture is carried out quarter of all land under cultivation in Malawi. Millions of urban in small spaces—patios, flower pots, small public spaces—ranging Africans cultivate vegetables and fruit trees in home gardens, from 1 m2 to 10,000 m2 . The crops grown in these areas are mostly both for their families and for sale. Urban agriculture is playing used for home consumption. Only natural fertilizers are used in a critical role in generating extra income for some of the more production. disadvantaged groups, especially low-income, female-headed households, and low-skilled populations. In Malawi, 700,000 urban Benefits residents practice home gardening to meet their food needs and Economy, Health, Education, Recreation. earn extra income. Source FAO Photo by Zeria N. Banda / World Bank Benefits Photo by Renzo Salvador on Unsplash http://www.fao.org/ag/agp/greenercities/en/ggclac/lima.html Economy, Health, Education, Social. Source World Bank http://documents1.worldbank.org/curated/ en/627721490623342886/text/ITM00184 Commercialization Partnership Coordinated Definition of Development of Boost local of agriculture between agro- investments -P158434-03-27-2017-1490623340300.txt metropolitan infrastructure economy and value chain businesses and by clusters of urban agriculture to reuse treated job creation smallholder production program water for farmers irrigation 136 137 REFERENCES Aerts, R., Dewaelheyns, V. and Achten, W.M. 2016. Potential ecosystem services of urban agriculture: a review. Peer J Llorach-Massana, P.; Muñoz, P.; Riera, M.R.; Gabarrell, X.; Rierdevall, J.; Montero, J.I.; Villalba, G. 2017. N2O emissions Preprints, 4, e2286v1. from protected soilless crops for more precise food and urban agriculture life cycle assessments. J. Clean. Prod. 149:1118–126. Agbonlahor, M.U., Momoh, S. and Dipeolu, A.O. 2007. Urban vegetable crop production and production efficiency. International Journal of Vegetable Science, 13(2) 63–72. Lovell, S.T. Multifunctional urban agriculture for sustainable land use planning in the United States. 2010. Sustainability, 2:2499–522. Agrawal, M., Singh, B., Rajput, M., Marshall, F. and Bell, J.N.B. 2003. Effect of air pollution on peri-urban agriculture: a case study. Environmental Pollution, 126(3)323–29. Mapanda, F., Mangwayana, E.N., Nyamangara, J. and Giller, K.E. 2005. The effect of long-term irrigation using wastewater on heavy metal contents of soils under vegetables in Harare, Zimbabwe. Agriculture, Ecosystems & Environment, 107(2- Artmann, M., and Sartison, K. The Role of Urban Agriculture as a Nature-Based Solution: A Review for Developing a –3)151–65. Systemic Assessment Framework. 2018. Sustainability 10(6)1937. DOI:10.3390/su10061937 Méndez, V.E., Lok, R. and Somarriba, E. 2001. Interdisciplinary analysis of home gardens in Nicaragua: Mmicro-zonation, Bernal, B., Murray, L.T., and Pearson, T.R.H. 2018. Global carbon dioxide removal rates from forest landscape restoration plant use and socioeconomic importance. Agroforestry Systems, 51(2)85–96. activities. Carbon Balance and Management, 13: 22 https://cbmjournal.biomedcentral.com/articles/10.1186/s13021-018-0110-8 Ober Allen, J., Alaimo, K., Elam, D. and Perry, E. 2008. Growing vegetables and values: Benefits of neighborhood-based community gardens for youth development and nutrition. Journal of Hunger & Environmental Nutrition, 3(4)418–39. Bradley, K. and Galt, R.E. 2014. Practicing food justice at Dig Deep Farms & Produce, East Bay Area, California: Self- determination as a guiding value and intersections with foodie logics. Local Environment, 19(2)172-–86. Olson, N. and Gulliver, J., 2011. Remediating Compacted Urban Soils with Tillage and Compost. CURA Reporter [Center for Urban and Regional Affairs, University of Minnesota], 41(3–4)31–35. Castro, D.C., Samuels, M. and Harman, A.E., 2013. Growing healthy kids: a community garden–based obesity prevention program. American Journal of Preventive Medicine, 44(3)S193-–S199. Orsini, F., Kahane, R., Nono-Womdim, R. and Gianquinto, G. 2013. Urban agriculture in the developing world: a review. Agronomy for Sustainable Development, 33(4)695–720. City of Vancouver. n.d. Urban Agriculture Design Guidelines for the Private Realm. Vancouver. https://vancouver.ca/files/ cov/urban-agriculture-guidelines.pdf Orsini, F., Michelon, N., Scocozza, F. and Gianquinto, G. 2008. Farmers-to-consumers: An example of sustainable soilless horticulture in urban and peri-urban areas. In International Symposium on the Socio-Economic Impact of Modern Cleveland, D.A.; Phares, N.; Nightingale, K.D.; Weatherby, R.L.; Radis, W.; Ballard, J.; Campagna, M.; Kurtz, D.; Livingston, Vegetable Production Technology in Tropical Asia. 809:209–220. K.; Riechers, G.; et al. 2017. The potential for urban household vegetable gardens to reduce greenhouse gas emissions. Landsc. Urban Plan. 157:365–374. Pandey, J. and Pandey, U. 2009. Accumulation of heavy metals in dietary vegetables and cultivated soil horizon in organic farming system in relation to atmospheric deposition in a seasonally dry tropical region of India. Environmental Climate Technology Centre & Network. n.d. Floating agricultural systems. https://www.ctc-n.org/technologies/floating- Monitoring and Assessment, 148(1)61–74. agricultural-systems Russo, A.; Escobedo, F.J.; Cirella, G.T.; Zerbe, S. 2017. Edible green infrastructure: An approach and review of provisioning Dumitrescu, Vlad. 2013. Mapping urban agriculture potential in Rotterdam. https://cms.4bg.nl/uploads/12/files/2013_ ecosystem services and disservices in urban environments. Agric. Ecosyst. Environ., 242:53–66. Mapping-Urban-Agriculture-Potential-in-Rotterdam_Report-Dumitrescu.pdf Smit, J., Nasr, J. and Ratta, A. 1996. Urban agriculture: Food, jobs and sustainable cities. New York, USA, 2:35–37. European Commission. 2020b, April. Nature-based Solutions for Climate Mitigation (No. 978-92-76-18200–9). Publications Office of the European Union. https://doi.org/10.2777/458136 Teig, E., Amulya, J., Bardwell, L., Buchenau, M., Marshall, J.A., and Litt, J.S. 2009. Collective efficacy in Denver, Colorado: Strengthening neighborhoods and health through community gardens. Health & Place, 15(4)1115–122. Food and Agriculture Organization of the United Nations (FAO). The State of the World’s Land and Water Resources for Food and Agriculture: Managing Systems at Risk. 2011. Earthscan: London, UK. Thapa, R.B. and Murayama, Y. 2008. Land evaluation for peri-urban agriculture using analytical hierarchical process and geographic information system techniques: A case study of Hanoi. Land Use Policy, 25(2)225–39. Gidlow, C.J., Randall, J., Gillman, J., Smith, G.R. and Jones, M.V. 2016. Natural environments and chronic stress measured by hair cortisol. Landscape and Urban Planning, 148:61–67. USDA. 2016. Urban Agriculture Tool Kit. (usda.gov) Grewal, S.S.; Grewal, P.S. 2012. Can cities become self-reliant in food? Cities, 29:1–11. Veen, E.J., Bock, B.B., Van den Berg, W., Visser, A.J., and Wiskerke, J.S. 2016. Community gardening and social cohesion: different designs, different motivations. Local Environment, 21(10)1271-–87. Haberman, D., Gillies, L., Canter, A., Rinner, V., Pancrazi, L., and Martellozzo, F. 2014. The potential of urban agriculture in Montréal: A quantitative assessment. Int. J. Geo-Inf., 3:1101–117. Wagstaff, R.K. and Wortman, S.E. 2015. Crop physiological response across the Chicago metropolitan region: Developing recommendations for urban and peri-urban farmers in the North Central US. Renewable Agriculture and Food Systems, Hallett, S., Hoagland, L., Toner, E., Gradziel, T.M., Mitchell, C.A. and Whipkey, A.L. 2016. Urban agriculture: 30(1)8–14. Environmental, economic, and social perspectives. Horticultural Reviews, 44:65–120. Waliczek, T.M., Zajicek, J.M. and Lineberger, R.D. 2005. The influence of gardening activities on consumer perceptions of Haq, A.H.M.R., Ghosal, T.K. and Ghosh, P. 2004. Cultivating wetlands in Bangladesh. Leisa Magazine, 20(4)18-–20. life satisfaction. Hort Science, 40(5)1360–65. Kaufman, J.L. and Bailkey, M. 2000. Farming inside cities: Entrepreneurial urban agriculture in the United States. Zeunert, J. and Waterman, T. eds. 2018. Routledge Handbook of Landscape and Food. Routledge. Cambridge, MA: Lincoln Institute of Land Policy. Lee, G.-G.; Lee, H.-W.; Lee, J.-H. 2015. Greenhouse gas emission reduction effect in the transportation sector by urban agriculture in Seoul, Korea. Landsc. Urban Plan. 140:1–7. 138 139 FACTS AND FIGURES DESCRIPTION Bioretention is a nature-based solution used to augment traditional gray stormwater and sewerage infrastructure. Bioretention areas are typically designed as shallow vegetated depressions that can intercept, infiltrate, divert, change volume and velocity, and treat stormwater flow. The type of soils, the depth of the landform, and the type of vegetation determine the efficiency and treatment capacity of a bioretention area. Bioretention areas can be particularly valuable in older cities with combined sewerage systems or with limited extent of pervious surfaces and a large volume of contaminated runoff. Well-designed, installed, and maintained bioretention areas can add measurable capacity to stormwater management systems. Correctly selected plants remove pollutants from stormwater and facilitate water table and aquifer recharge. Bioretention areas can be adapted to a variety of urban environments. It can take many forms and shapes for different functions and contexts. Bioretention basins, vegetated swales, rain gardens, retention ponds, infiltration trenches, and detention ponds are some examples of bioretention systems. Depending on the stormwater volume to be collected, a water retention area can be either dry or wet. When bioretention systems are systematically planned and implemented, they can add to the richness of urban green infrastructure, enhance biodiversity, and deliver aesthetic, recreational, educational, and quality of life benefits. TYPE OF CITY SCALE APPROACH Neighborhood Rehabilitate, Restore, Enhance Upgrade of existing roadside drainage Coastal Delta Installation of green strips along streets and City public spaces. River basin Create River Mountain Construct new bioretention areas. Cooling effect PROCESSES Carbon sequestration Evapotranspiration Shade Biodiversity Water collection BIORETENTION AREAS Water and soil cleaning Sewer overflow Infiltration Menomonee Valley, Milwaukee, WI, USA Photo by Aaron Volkening on Flickr 140 141 VISUALIZATIONS VISUALIZATION OF BIORETENTION AREAS IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR BIORETENTION AREAS Bioswales and rain gardens Bioswales and rain gardens are shallow, densely vegetated ground depressions, with a variety of trees, shrubs, and grasses to collect stormwater from adjacent impervious surfaces. During storms, they become flooded and facilitate ground infiltration and cleaning of stormwater simultaneously (EPA 2006). During dry seasons, swales and rain gardens contribute to the quality of public areas. Bioswales are common in streets and other linear infrastructure; rain gardens are common in parks, squares, and private gardens. 1 Detention pond 3 Detention ponds are deeper and less biologically diverse bioretention areas than bioswales and rain gardens. Bioretention systems capture and temporally store stormwater during periods of 2 heavy rain (Eisenberg and Polcher 2020). Detention ponds can be completely filled up with water during storms; they infiltrate much of it into the ground; and discharge the overflow into the sewer system. The remainder of the time they remain dry. Detention ponds can provide attractive scenic elements in public areas, around playgrounds and sport fields. Retention pond Retention ponds are bioretention areas characterized by a permanent body of water and vegetated edges. Unlike detention ponds, they are permanently filled with water. Retention ponds collect stormwater from the surrounding areas; add storage capacity Details of increased benefits for the and ease the pressure on the surface water treatment and sewerage urban living environment systems. Retention ponds offer the added benefit of storing water for further reuse during drought conditions, while simultaneously providing habitat and enriching the diversity of public green spaces (Iwaszuk et al. 2019). 1 2 3 Permeable pavements Permeable pavements are alternatives to traditional pavements, such as pervious asphalt, pervious concrete, interlocking pavers, and plastic grid pavers, and are especially effective during less intense storms (LIDC 2007) for reducing surface runoff. They infiltrate, treat, and store rainwater and reduce runoff by allowing rain and snowmelt to seep to underlying layers. They generally consist of a surface pavement layer, an underlying stone aggregate reservoir layer, and a filter layer or fabric installed at the bottom. Bioretention areas create Introduction of bioretention Linear bioretention areas improve Permeable pavements can be used at commercial, institutional, and natural and ecological spaces areas into streetscape reduces the transition between public and residential sites in spaces that are traditionally impervious, such as for local residents the dominance of cars and gray private spaces in cities. pedestrian walkways, driveways, bike lanes, parking lots, and low- to recreate. infrastructure, bringing nature into volume roadways. They are unsuitable for high-volume or high- public spaces. speed roadways and avoided at spill sites as they clog the pavement (WRI and WBG 2019). 142 143 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of bioretention areas. The diagram in this section shows a sampling of important benefits that bioretention areas can provide to people. Water quality and sediment management Pluvial flood risk reduction Social interaction Pluvial flood regulation Biodiversity Heat Subsidence regulation regulation BIORETENTION AREAS Soil pollution Education regulation Water pollution regulation Carbon storage and sequestration Stimulate local economies and job creation Pluvial flood risk reduction: Bioretention systems are generally Biodiversity: Bioretention areas provide important habitats; Pluvial flood regulation: Bioretention areas reduce pluvial flooding and mitigate peak water loads on the sewerage and stormwater designed to reduce pluvial floods by slowing and attenuating support biodiversity by improving ecological connectivity, systems by collecting, infiltrating, and storing stormwater. Literature acknowledges that the effectiveness of bioretention NBS greatly stormwater. These systems are typically designed to address providing food and pollination, preserving terrestrial and depends on their design and the frequency and the magnitude of rainfall, and on their ability to increase storage capacity using stormwater locally at the source and therefore, generally semiaquatic habitats, and linking the urban environment to the existing open spaces (Ruangpan et al. 2020). Rain gardens are more effective in dealing with small discharge of rainwater (Ishimatsu serving only a small catchment area. A suite of these small- surrounding countryside (Kim and Song 2019). et al. 2017), while bioswales are better suited for flood reduction during heavier and shorter rainfall (Zölch et al. 2017). Several scale interventions applied throughout the catchment however Social interaction: Bioretention areas provide benefits to improve studies of bioretention basins in the city of Calgary, Canada, demonstrated up to 90% reduction of runoff volume (Khan et al. 2013), contribute to reducing the effects of larger floods in downstream quality of life. They also create opportunities for recreation in and peak flow reduction of up to 41.65% in Hai He Basin, China, (Huang et al. 2014). areas. public spaces and create informal social gathering spaces (Kim Carbon storage and sequestration: Depending on the design, and Song 2019). These systems can be used to engage the public Heat regulation: Bioretention areas reduce heat by lowering surface and air temperatures through vegetative evapotranspiration. the materials and the species used, bioretention areas sequester in their planning and maintenance to build stronger community and store carbon. According to an estimate by the European cohesion. Designs can combine bioretention areas with traffic Other functions: Bioretention areas are effective in removing pollutants from water and soil (Kennen and Kirkwood 2015). They Commission, the average carbon sequestration rate is 12.5 kg control and regulation measures, which can improve the safety can remove organic pollutants, nitrogen contamination and heavy metals from stormwater (LIDC 2007). Water reabsorbed by the carbon/m2 (EC 2020b). and spontaneous use of public spaces. ground also helps stabilize and prevent soil subsidence. Stimulate local economies and job creation: Bioretention Water quality and sediment management: Bioretention areas areas improve the image and market value of real estate and are typically designed to capture and treat the first flush of improve economic development opportunities. Bioretention stormwater runoff–the initial wave of runoff that carries the areas can generate green jobs and increase productivity among highest amount of pollutants. While effectiveness varies, some employees in locations with access to these areas (Kim and Song bioretention areas have been shown to remove up to 90% of 2019). heavy metals from stormwater, organic pollutants, and nitrogen Education: Bioretention areas increase recreational and contamination (Kennen and Kirkwood 2015). educational opportunities, by raising awareness of environmental issues and providing opportunities for interacting with nature in an urban environment (Kim and Song 2019). 144 145 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: A bioretention area is considered an on-site stormwater management solution. Planting and growing strategy: Selection of appropriate plant species is essential for the effective Its design should factor in the major differences between temperate countries and tropics, including functioning of the bioretention areas. Native floodplain species tolerant of variability in soil saturation variations in the amount and pattern of rainfall and stormwater runoff, nutrients concentration, and land and inundation and resilient to environmental stress are often best suited to the variable environmental use (Goh et al. 2019). conditions. However, consideration must also be given to changes in plants and soils, which may vary from areas of regular inundation to areas that are seldom saturated. Hydrology: Understanding hydrological conditions is critical to the design of bioretention areas. Bioretention areas should always remain above the water table to ensure that groundwater does not Hybrid infrastructure: Bioretention areas can be effectively combined and connected with sewer systems intersect the filter bed and reduce infiltration capacity. Unless an impermeable liner is installed, a distance through an overflow outlet or through underdrains that connect to the sewer system. By attenuating of at least 0.6 meters should be maintained between the bottom of the excavated bioretention area and runoff, bioretention areas relieve the pressure of runoff and contribute to storm water management— the seasonally high ground water table (DDOE 2012). integrating green and gray. Soil: Soil for bioretention areas typically include mixed soils or engineered media. High infiltration rates of the media are key. To ensure drainage capacities, well-draining soils are often considered during the URBAN design. The underlying soils typically have low infiltration rates and as such, underdrains can be part of the design (DDOE 2012; MSW 2018). Land use: Residential, commercial, and industrial streets and infrastructure networks, urban parks Water quality: Depending on the type of soil and plants, bioretention areas can effectively collect polluted of various types, squares, gardens, parking areas, and private gardens are all suitable land uses for stormwater runoff by removing, trapping, and degrading organic contaminants, converting nitrogen bioretention areas. contaminants into gas and returning them to the atmosphere, capturing and immobilizing inorganic contaminants (Kennen and Kirkwood 2015). Urban density: Suitable urban density for bioretention areas ranges from low to medium. TECHNICAL Area: Small to medium. Bioretention areas are nature-based solutions typically designed for application at a neighborhood or district scale. Slope: Bioretention areas perform the best with contributing slopes greater than 1% but less than 5% (DDOE 2012). Integrated urban planning: Bioretention areas can be implemented as part of a street renewal, sewerage system upgrade and capacity expansion, local green initiatives, and stormwater drainage installation for Substrate: The substrate should comprise a loamy soil capable of providing infiltration and supporting new development areas. a healthy vegetative cover. The soil can be improved with composted organic material. A secondary filtration layer, composed of sand, gravel, or similar drainage material, is often placed below the substrate to enhance the infiltration and water cleaning process (DEP 2006). MAINTENANCE Dimensions: Bioretention surface area should be sized at approximately 3% to 6% of the contributing Bioretention systems require intensive and regular maintenance to avoid clogging with sediments. The basins should be drainage area depending on the extent of impervious surfaces. The depth of the pond depends on the inspected monthly to identify further maintenance requirements; litter and plant debris should be removed, and eroded amount of stormwater to be treated. Bioretention areas work best with small contributing drainage areas areas should be restored (Iwaszuk et al. 2019). that facilitate an even distribution of stormwater flow over the filter bed (DDOE 2012). 146 147 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land is Costs of bioretention areas are a Maintenance costs of bioretention required for bioretention areas. function of the type of bioretention areas are also a function of the solution installed, the complexity type and complexity of bioretention Land on which bioretention areas of installation, initial site conditions solution installed, the types of trees may be located may be public or and characteristics, and labor and and vegetation planted, and local private. material costs. Potential bioretention climatic conditions. Maintenance solutions range from low-cost activities may include debris removal, Land area required for bioretention investments (e.g., detention ponds) weeding, and pruning. areas will vary from smaller to larger to more expensive bioretention areas, raising transaction costs if solutions (e.g., bioretention basins). engagement and collaboration with multiple landowners and stakeholders is necessary. Example land-related costs: • Acquisition costs • Land use (e.g., payments to landowners) costs • Land protection costs, including managing and controlling access UNIT COST EXAMPLES THROUGHOUT THE GLOBE Construction and implementation Maintenance • Detention ponds: US$60/m2 (US$600,000/ha). • Annual operation and maintenance costs as a • Infiltration trenches: US$74/m2 (US$740,000/ percentage of construction costs range from ha). 0.5 – 10% for all sustainable drainage systems • Vegetated bioswales: US$371/m² (SUDS) components, including bioretention, in a (US$3,710,000/ha). United Kingdom study, or an annual cost range in • Public rain gardens: US$501/m² (US$5,010,000/ the range of US$0.1–US$2/m2/year (US$1,000– ha). US$20,000/ha/year) (FCERM and EA 2021). • Bioretention basin: US$534/m² (US$5,340,000/ • Detention basin: US$0.14–US$0.40/m2 ha) (Costs estimated from global sources in (US$1,400–US$4,000/ha) of detention basin Ruangpan et al. 2020). area annually; US$345–US$1,379 per basin (US$3,450,000–US$13,790,000/ha) (cost from the UK). • Infiltration trenches: US$0.3–US$1.4/m2 (US$3,000–US$14,000/ha) of filter surface area annually (cost from the UK). • Infiltration basin: US$0.14–US$0.41/m2 (US$1,400–US$1,400/ha) of basin area annually (cost from the UK) (FCERM and EA 2021). Milwaukee, WI, USA Photo by Aaron Volkening on Unsplash 148 149 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned in bioretention areas, drawn from the growing experience in implementing NBS throughout the globe. Project #1: St. Kjeld’s neighbourhood: Tåsinge Plads, 2013–15 Project #3: Street Edge Alternatives (SEA Streets) Completed Spring Location: Copenhagen, Denmark 2001 Description: The bioretention project is part of ‘The Climate Location: Seattle, USA Neighborhood’ project, in the St. Kjeld’s neighborhood, launched Description: The Street Edge Alternatives (SEA Streets) project as a neighborhood renewal program. The bioretention area was introduced bioretention, along a typical curbless neighborhood sloped to collect rainwater at the bottom, where it seeps into the street with informal drainage infrastructure and traffic calming. ground instead of being directed to the drains. Water from the The project created a sense of place and community in the streets collects in waterbeds, which are filled with mould that filters neighborhood. The project helps local residents understand the water. This climate adaption creates capacity in the drains to their own role and contribution to managing stormwater and prevent flooding. The entire St. Kjeld’s neighborhood is a showcase environmental impacts. The addition of a sidewalk that separates for ground-breaking climate adaptation solutions. pedestrians from traffic increased the feeling of safety. As a result of this project, many community members have become stewards in Benefits efforts to improve water quality and stream health in Pipers Creek. Health, Flood and Heat Stress Risk Reduction. SEA Street has created environmental awareness and community Photo by Google Earth Source Photo by Chris Hamby On Flickr action. City of Copenhagen, HOFOR, GHB Landskabsarkitekter https://urban-waters.org/sites/default/files/uploads/docs/tasinge_ Benefits plads.pdf Health, Education, Flood and Heat Stress Risk Reduction. Source Showcase for Integrated in Participatory Integrated in Infrastructure Participatory Seattle Public Utilities, Seattle Department of Transportation climate-proof neighborhood process with sewerage system renewal and process with https://nacto.org/case-study/street-edge-alternatives-sea-street- public space renewal local expansion traffic calming local pilot-seattle/ program communities strategy communities Project #2: Dar es Salaam Metropolitan Development Project, Project #4: Araucárias Square: Rain Garden and Pocket Forest, 2015–22 2017–18 Location: Dar es Salaam, Tanzania Location: Sao Paulo, Brasil Description: The City of Dar es Salaam has undergone a period of Description: This is the first rain garden implemented in a Brazilian unprecedented urbanization, contributing to the degradation of city in 2017 with the active involvement of residents. The garden the natural environment. With a growth rate near or above 5% collects runoff across a surface of 900 m² that would otherwise for the past three decades, Dar es Salaam is the fastest growing go directly into the drainage system, and which used to flood city in East Africa. The development objective of the Dar es lower areas of the city. After its implementation, the vegetation Salaam Metropolitan Development Project is to improve urban thrived and runoff has been reduced. Residents and leaders of services and institutional capacity in the metropolitan area, and the grassroots movements actively participated to transform this to facilitate potential emergency response. The project comprises remnant derelict piece of land. Social media was also used to invite infrastructure improvements and constructions of primary and and motivate other volunteers in the collective efforts to plant pocket secondary drainage systems—including bank stabilization detention forests in small plots of land. This social experience, with people ponds—and connection to a secondary network around five river of all ages coming from various districts to actively contribute to Photo by Carlos Felipe Pardo on Flickr basins. Photo by Ricardo Cardim / CARDIM Arquitetura Paisagística nature's reconstruction in the park, has also led to private funding contributions to maintain and protect the new pocket park. Benefits Benefits Health, Economy, Flood and Heat Stress Risk Reduction. Community, Education, Identity, Flood and Heat Stress Risk Source Reduction. World Bank Source Integrated in a Provision of External Showcase Community and Funded by comprehensive institutional funding https://projects.worldbank.org/en/projects-operations/project- for climate local stakeholder local resident CARDIM Arquitetura Paisagística task of city capacity and detail/P123134 adaptation involvement https://oppla.eu/casestudy/20079 recovery urban services http://www.cardimpaisagismo.com.br/portfolio/largo-das- araucarias/ 150 151 REFERENCES Dept. of Environmental Protection (DEP). 2006. Stormwater Best Management Practices (BMP) Manual. Pennsylvania. design. Water, 5(1) 13-–28. https://pecpa.org/wp-content/uploads/Stormwater-BMP-Manual.pdf District Department of the Environment. Stormwater Management. Guidebook. Watershed Protection Division. District of Columbia, Washington D.C. https://nacto.org/docs/usdg/stormwater_management_guide_district_columbia.pdf Eisenberg, B. and Polcher, V. 2020. Nature-Based Solutions Technical Handbook. UNaLab Horizon. https://unalab.eu/ system/files/2020-02/unalab-technical-handbook-nature-based-solutions2020-02-17.pdf European Commission. 2020b, April. Nature-based Solutions for climate mitigation (No. 978-92-76-18200–9). Publications Office of the European Union. https://doi.org/10.2777/458136 European Commission. (2020c, April). Nature-Based Solutions for Flood Mitigation and Coastal Resilience (No. 978-92- 76-18198–9). Publications Office of the European Union. https://doi.org/10.2777/374113 Flood and Coastal Erosion Risk Management Research (FCERM) and Development Programme and Environment Agency. Govt. Of UK. (FCERM and EA. 2021. Long-term costing tool for flood and coastal risk management. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/411509/Cost_ estimation_for_SUDS.pdf Goh, H.W., Lem, K.S., Azizan, N.A., Chang, C.K., Talei, A., Leow, C.S., and Zakaria, N.A. 2019. A review of bioretention components and nutrient removal under different climates—future directions for tropics. Environmental Science and Pollution Research, 26(15)14904–919. Huang, J.J., Li, Y., Niu, S., and Zhou, S.H. 2014. Assessing the performances of low impact development alternatives by longterm simulation for a semi-arid area in Tianjin, northern China. Water Science and Technology, 70(11) 1740–45. Ishimatsu, K., Ito, K., Mitani, Y., Tanaka, Y., Sugahara, T., and Naka, Y. 2017. Use of rain gardens for stormwater management in urban design and planning. Landscape and Ecological Engineering, 13(1)205–12. Iwaszuk, E., Rudik, G., Duin, L., Mederake, L., Davis, M., Naumann, S., and Wagner, I. 2019. Addressing Climate Change in Cities. Catalogue of Urban Nature-Based Solutions. Ecologic Institute, the Sendzimir Foundation: Berlin, Krakow. https:// www.ecologic.eu/sites/files/publication/2020/addressing-climate-change-in-cities-nbs_catalogue.pdf Kennen, K. and Kirkwood, N. 2015. Phyto: Principles and resources for site remediation and landscape design. Routledge. Khan, U.T., Valeo, C., Chu, A., and He, J. 2013. A data driven approach to bioretention cell performance: prediction and design. Water, 5(1)13–18. Kim, D. and Song, S.K. 2019. The multifunctional benefits of green infrastructure in community development: An analytical review based on 447 cases. Sustainability, 11(14)3917. Low Impact Development Center (LIDC). 2007. “Low Impact Development Center (LIDC) Urban Design Tools.” https:// www.lid-stormwater.net/ Minnesota Stormwater Manual. BMPs for stormwater filtration. 2018. https://stormwater.pca.state.mn.us/index. php?title=BMPs_for_stormwater_filtration Ruangpan, L., Vojinovic, Z., Sabatino, S.D., Leo, L.S., Capobianco, V., Oen, A.M., McClain, M.E., and Lopez-Gunn, E. 2020. Nature-based solutions for hydro-meteorological risk reduction: a state-of-the-art review of the research area. Natural Hazards and Earth System Sciences, 20(1)243–70. https://nhess.copernicus.org/articles/20/243/2020 WRI and WBG. 2019.NBS for Urban Disaster Risk Management. (Powerpoint slides). World Resources Institute and the World Bank Group. https://drive.google.com/drive/folders/1wmZUJ3A9R42usUh9rdvYRtAbjB8cyMMj Zölch, T., Henze, L., Keilholz, P., and Pauleit, S. 2017. Regulating urban surface runoff through nature-based solutions–an assessment at the micro-scale. Environmental Research, 157:135–44. Minneapolis, MN, USA Photo by Minneapolis Public Works TPP on Flickr 152 153 FACTS AND FIGURES DESCRIPTION Natural inland wetlands are highly biodiverse, productive ecosystems that form an interface of land and water, and deliver valuable ecosystem services. Historically, their value has been largely misunderstood leading to their destruction in many parts of the world. In recent decades however, cultural attitudes toward wetlands have changed as their ability to protect cities from floods gained recognition. For a long time perceived as wastelands and prime areas for urban infill projects, natural inlands wetlands are now increasingly recognized as critical environmental infrastructure that can contribute to address climate change effects in cities. Wetlands sequester carbon, and in some cultures, their plants are harvested for building materials and food. They work as a natural sponge against flooding and drought and help offset climate change. Natural inland wetlands are frequently or continuously inundated by water. They are also home to a special type of wet feet-tolerant plants and the vegetation has adapted to saturated soil conditions that filter, remove sediment, nutrients, and pollutants from water. These wetlands also provide habitat for wildlife, fish, other aquatic, threatened, and endangered species. They are an extraordinary scenic and recreational asset, increase biodiversity, and provide opportunities for birdwatching and hiking in nature. Successful natural inland wetland restoration projects are delivering tangible climate adaptation benefits, and many cities have granted them protection status, and initiated rehabilitation efforts. There is a great diversity of wetland types worldwide that range in character from wet meadows, marshes, and vegetated floodplains. TYPE OF CITY SCALE APPROACH Neighborhood Protect Protect and preserve existing natural inland Coastal Delta wetlands and their hydrological processes. City Rehabilitate, Restore, Enhance Rehabilitate existing wetlands and restore or River basin enhance their natural functions so they can River Mountain deliver ecosystem services. PROCESSES Cooling effect Carbon Sediment sequestration Water buffer trapping Biodiversity NATURAL INLAND WETLANDS Cleaning Groundwater recharge Lisbon,Portugal Photo by Mário Rui André on Unsplash 154 155 VISUALIZATIONS VISUALIZATION OF NATURAL INLAND WETLANDS IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR NATURAL INLAND WETLANDS Drainage reduction Natural inland wetland areas have been used for agriculture in 1 many regions around the world. To make the land suitable for crops, drainage systems are installed to control the water table and provide irrigation. To reverse the destruction of the wetland, natural water fluctuation must be restored together with the composition of the 3 anaerobic hydric soil formed over a long period. The first step is to remove a section of the underground agricultural tile that is draining the wetland basin or create a ditch plug by building an earthen wall to impound water. 2 Improving lateral connectivity In many urban contexts, canals and artificial berms were built to disconnect the main water body from the floodplain and its wetland. This resulted in the disruption of wetland hydrology. Rehabilitation would require a reversal of this action and an improvement of lateral connections between the main body of water and the wetlands. Re- establishment of lateral connections will reactivate wetland areas and improve its environmental performance. It will also bring back Details of increased benefits for the the waterfowl and other wetland biota. urban living environment 1 2 3 Maintenance and cleaning The health of a natural inland wetland and its environmental performance depends on proper lateral connections, hydrological cycles, the right soils, and plants. Invasive plants can push out native species, wreak havoc in the natural wetland habitat, change flow patterns and degrade the water quality. In some instances, degradation can be offset by restoring natural hydrological Wetlands form an interface between Natural wetlands provide excellent A combination of habitats conditions; however, undesired invasive plants may need to be land and water. They are a part of opportunities for communities to contributes to aesthetic and controlled through appropriate mechanical, chemical, or biological both the aquatic and the terrestrial connect with nature and learn about the biodiversity values. Open water areas control measures. ecosystem and function as a two- broad suite of values that nature-based offer recreational options such as way buffer, mitigating storms and solutions provide, especially when trails kayaking and boating. assimilating pollutants. and educational facilities are integrated. 156 157 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of natural inland wetlands. The diagram in this section shows a sampling of important benefits that natural inland wetlands can provide to people. Riverine flood Water quality and regulation Pluvial and riverine sediment management flood risk reduction Pluvial flood regulation Resources production Biodiversity Bank erosion NATURAL INLAND regulation WETLANDS Heat regulation Tourism and recreation Water pollution regulation Carbon storage and Biodiversity sequestration Drought Stimulate local economies regulation and job creation Pluvial and riverine flood regulation: Certain inland wetlands attenuate stormwater flow by spreading it evenly across their flat and Pluvial and riverine flood risk reduction: Natural inland wetlands the last remaining pieces of natural habitat in cities. As such, they wide terrain, instead of confining it to a narrow channel. This way they can hold back considerably more stormwater, while infiltrating mitigate floods in urban environments and protect urban rivers offer a possibility to contemplate nature and engage in a whole and removing the sediment and pollution and stabilizing the water table (Ozment et al. 2019). The potential for flood attenuation by capturing, buffering, and storing stormwater (Wood and van range of activities such as fishing, hiking, nature observation and varies across wetlands and is based on their size, vegetation and soil type, shape and capacity of the basin, and other factors. Halsema 2008), reducing the velocity and the amount of peak photography, bird watching, canoeing, and boating (Wood and stormwater flow, and preventing large quantities of untreated van Halsema 2008). Large wetlands support important wildlife Heat regulation: In highly humid conditions, the rate of wetland evapotranspiration significantly impacts local and regional climate water from entering the water bodies (Maltby 1986). populations and offer significant tourism potential. (Roggeri 2013). Studies suggest that wetlands may have cooling effect. For example, a study conducted in Mexico City measured the Water quality and sediment management: The practice of using Carbon storage and sequestration: Wetlands are globally effect of wetlands on temperature and recorded an incremental rise of about 2°C (35.6°F) every 35 meters as the distance from the natural inland wetlands to treat wastewater and improving water important carbon sinks, storing vast amounts of carbon and body of water increased (Wetlands International 2020). Heat reduction can be further increased in areas with large, dense canopy quality in urban environments has been around for hundreds thereby helping to mitigate climate change. Peatlands, in trees or if the airflow can pass unobstructed across the open water areas. of years (McEldowney et al. 1993). Research on the ability of particular, hold a disproportionate amount of the earth’s soil wetlands to purify water has shown that anaerobic conditions— carbon while inundated wetlands can potentially sequester Other functions: In urban environments wetlands extract pollutants from the surface water, lessen stream erosion, recharge typical of wetlands—enhance the retention of many compounds substantial amounts of soil carbon over the long term because of groundwater, store stormwater, and release it during dry periods (Wood and van Halsema 2008). Natural inland wetlands mitigate and facilitate processes such as denitrification, ammonification, slow decomposition and high primary productivity, particularly the loss of biodiversity in urban environments and provide key habitats for local and migratory species. and the formation of insoluble phosphorous metal complexes in climates with long growing seasons (Valach et al. 2021). (Bastian and Benforado 1988). Inland wetlands also act as Sequestration rates increase with vegetation cover (Valach et natural sediment traps with the slow flow of water through al. 2021) and are likely to be higher for woody than herbaceous wetland vegetation promoting sediment deposition. Elevated systems. Drained or damaged wetlands on the other hand, rates of sediment accumulation may however lead to a tipping are a major source of greenhouse gas emissions since human point where erosion leads to a loss of sediment from the system. disturbance, particularly drainage, releases carbon in CO2, Biodiversity: Wetlands are one of the most productive habitats leading in years to the loss of carbon that accumulated over in the world, with greater species diversity, nutrient recycling, centuries or millennia. The wise use and restoration of natural and niche specialization than most other ecosystems. Almost inland wetlands is therefore essential to protect stored carbon all the world’s waterbirds and migratory birds use wetlands as and reduce avoidable carbon emissions (The Ramsar Convention feeding, migratory way-stations and breeding grounds (CBD Secretariat, 2018). 2015). Stimulate local economies and job creation: As wetlands have Resource production: In many cultures, wetlands are important a significant tourism potential, they can stimulate the local sources of food and building materials. These uses need to be economy, for example by creating park ranger and service jobs. carefully managed so as not to undermine other ecological Practices to harvest food and building materials have a direct functions, which require balancing agricultural uses and needs economic impact on the livelihoods of local people (Chabwela of biodiversity (Wood and van Halsema 2008). and Haller 2010; Barbier et al. 1997; Van der Duim and Henkens Tourism and recreation: Natural inland wetlands are some of 2007). 158 159 SUITABILITY CONSIDERATIONS ENVIRONMENTAL TECHNICAL Location and climate: Natural inland wetlands have wide geographic distribution and can be found in Planting and growing strategy: Wherever possible, only native plant species should be used in wetland every climate. Nearly half of the world's wetlands are found between 50°–70°N latitude in the peat-rich rehabilitation projects. Plant selection should focus on the compatibility of plants and soils, the ability boreal and arctic regions where bogs and fens are abundant. More than one-third of the Earth's wetlands of plants to trap pollutants, and ability to withstand and influence the velocity of water moving through exist between 20°N and 30°S latitude, where forested wetlands and marshes prevail (including tropical the wetland. Guidance for plant selection can be gained by visiting natural wetlands of a similar type and rainforests and floodplain wetlands). The remaining 20% may be found in temperate zones (Tiner 2009). catchment context. Hybrid infrastructure: When heavily degraded, gray infrastructure such as levees, low berms, diversions, grade stabilization and water control structures, can be used to restore and enhance key wetland functions. Hydrology: Watershed dynamics and the character of the urban environment—in particular the extent of These artificial inclusions are typically necessary to prevent erosion and incision associated with increased paved area—define the hydrology of natural inland wetlands in urban areas. These parameters are part catchment runoff. These structures, however, can be susceptible to damage during flood events, and the of its composition (Faber-Langendoen et al. 2008): strengths and weaknesses of different options should be considered in the design. Sources of water: Natural inland wetlands are supplied by runoff from the immediate catchment area, direct precipitation and any connected river or a lake. They may also be URBAN recharged by ground water. Water inputs in urban wetlands typically differ considerably from rural wetlands, with a reduction in low flows and an increase in the magnitude and intensity of storm events often radically altering natural water inputs. Hydrologic connectivity: A wetland's connection to the adjacent body of water and its Land use: Suitable land uses for inland wetland restoration are water areas, green areas, and nature relationship to the rest of the green infrastructure in the city determines how the water reserves. moves in and out of the wetland. This connectivity affects the amount of sediment and pollutants to be processed by the wetland. Upstream surface water retention: At the scale of a watershed, the amount of water that reaches a wetland depends on how much is intercepted and abstracted on the way by water Urban density: Suitable urban density for wetland restoration depends on the location of existing storage facilities, such as reservoirs, sediment basins, retention ponds, paved and unpaved wetlands, but are generally low to medium. surfaces, and other factors that can reduce the volume. Hydroperiod: The hydroperiod is the time of which a wetland is inundated by water per year. In some regions, natural inland wetlands have daily cycles governed by diurnal increases in Area: Medium to extra-large. Wetland protection and restoration is a nature-based solution typically evapotranspiration, and seasonal cycles governed by the wet season rainfall, stormwater implemented at city to river basin scale. runoff, and higher levels of water consumption during the dry season (Faber-Langendoen et al. 2008). Integrated urban planning: Wetland restoration can be conducted as part of an environmental Soil: Natural inland wetlands are generally found in the lower areas of the watershed. Their location conservation program, development of green areas and public parks. Wetland restoration can also be coincides with areas of hydric soil accumulation. Hydric soils are formed when soils are highly saturated integrated and funded as part of stormwater management upgrading. or flooded for such a long time that the upper strata become anaerobic. These soils can then sustain water levels appropriate for wetland plants (Covington et al. 2003). MAINTENANCE Landscape integration: While typically connected to the drainage network, the habitat value of a natural inland wetland is strongly influenced by its connection to other natural habitats. Buffer zones and green Natural inland wetlands are subject to encroachment, degradation, invasion by exotic species, accidental contamination, corridors that connect wetlands with the broader open space network of a city should therefore be and other unforeseen circumstances. Regular monitoring and maintenance may be required to keep them healthy, maintain enhanced wherever possible. desirable plant communities, and remove exotic species and excessive sediment (NOAA et al. 2003). Wetlands may also require burning or mowing to maintain desirable plant communities. 160 161 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land The costs of protecting and Long-term maintenance costs of is required for protection and restoring or rehabilitating natural natural inland wetlands will be site- restoration of natural inland inland wetlands vary according to specific and may include activities wetlands. wetland size, hydrology, location, such as buffer mowing and invasive and condition; opportunity costs of species removal. Costs associated Land on which natural inland protecting the wetland; and labor with maintaining natural inland wetlands may be located could be and material costs. Larger wetland wetlands is generally lower than public or private. areas are likely to have greater costs those of constructed wetlands where of protection and restoration, though natural wetland ecosystem processes The size of natural inland wetland economies of scale may result from are well-established. areas will vary from smaller to larger larger projects. areas, raising transaction costs if engagement and collaboration with Natural inland wetland restoration multiple landowners and stakeholders costs vary depending on the intensity is necessary for protection and of the restoration actions needed restoration. to restore hydrologic function. Example land-related costs: Actions may range from channel filling and tile drainage removal to • Acquisition costs erosion control, excavation of infill • Land use (e.g., payments to material or reshaping activities. In landowners) costs many instances, wetland restoration • Land protection costs, including also involves the integration of gray managing and controlling access infrastructure structures to manage flows and control water levels. Restoration also typically includes reintroducing plant and animal species through planting vegetation and transporting wetland species to the project site. UNIT COST EXAMPLES THROUGHOUT THE GLOBE • Natural inland wetland protection (permanent of phosphorus loads from open water bodies in wetland easement) and restoration costs in the Florida) (TEEB 2011). US have been estimated to range from US$170 • Buffer mowing is estimated to cost US$3 acre/year –$6,100/acre (US$420–US$15,067/ha) (Hansen (US$7.41/ha/year) in the US (Iowa) (Plastina and et al. 2015). Johanns 2016). • Natural inland wetland restoration costs were • Annualized costs of natural inland wetland estimated at US$9,900/ha (restoration through restoration over a 40-year lifespan in Iowa: hydrologic manipulation in Denmark); and US$785/acre/year (US$1,939/ha/year) (EPA US$30,000/ha (restoration through removal 1995). Tin Shui Wa, Hong Kong Photo by Easton Mok on Unsplash 162 163 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned about natural inland wetlands, drawn from the growing popularity of NBS throughout the globe. Project #1: East Kolkata Wetlands, 2006 to date Project #3: Qunli National Urban Wetland, 2006–21 Location: Kolkata, India Location: Qunli New Town, China Description: Spread over 12,500 hectares on the eastern side Description: Qunli New Town is a new district on the outskirts of of the city of Kolkata, this natural wetland is a Ramsar site and Haerbin City in North China. It was built to accommodate 350,000 one of the largest wastewater-fed aquaculture systems in the new residents in over 32 million m2 of buildings in 2010. 16.4% world. It provides fishing opportunities for locals and supports of the land to develop was zoned as permeable green space. The paddy and vegetable cultivation in small plots in and around rest of the former flat plain was covered in impervious concrete. the wetland system. The wetlands serve two functions that may A 34.2-hectare park was designed on a former wetland area to seem contradictory at a first glance: they are the city’s free mitigate flooding. Stormwater from the newly developed urban sewerage works and they are also a fertile aquatic market garden. area is collected in a pipe around the circumference of the wetland. Wastewater is used in paddy fields and vegetables are grown on the The water is filtrated in the ponds and then deposited into the verdant banks and on a long, low hill created by Kolkata’s organic wetland. Native wetland grasses and meadow grow in the ponds waste. Wetlands are also a habitat for fish. Not only do these at various depths and following the natural evolution process. A wetlands provide affordable food and vegetables for the city, they recreational area was integrated into the park for sports and leisure Photo by Bing maps also provide livelihood for about 1.1 million people. Photo by Kongjian Yu / Turenscape activities. Benefits Heritage, Economy, Water quality, Flood and Heat Stress Risk Benefits Reduction. Biodiversity, Health, Social, Flood and Heat Stress Risk Reduction. Source Source Wetland protection City largely Community East Kolkata Wetlands Management Authority (EKWMA) Restoration Creation of a Showcase for Haerbin City Municipality and Turenscape approach. depends on sensitivity and http://ekwma.in/ek/ approach new urban park water urbanism http://landezine.com/index.php/2014/01/qunli-national-urban- Conservation and wetlands local heroes for https://www.theguardian.com/cities/2016/mar/09/kolkata- for existing and recreation approach wetland-by-turenscape/ Management Act resources conservancy wetlands-india-miracle-environmentalist-flood-defence wetlands amenities Project #2: Oroklini Wetland Restoration, 2012–14 Project #4: Zambia Wetland Restoration Efforts, 2011–33 Location: Larnaca, Cyprus Location: Kafue Flats, Zambia Description: Oroklini lake is located close to the south coast Description: WWF Zambia has worked to protect and restore of Cyprus next to the city of Larnaca within the boundaries of wetlands and freshwater ecosystems for more than 50 years. It then Oroklini village. The waterbody has undergone modifications engaged organizational and private sector stakeholders in a water and degradation since the 1940s, when the lake was dried out to stewardship approach in a 30-year project to restore the Kafue alleviate the fear of diseases. The objective of the natural water Flats floodplain grasslands while simultaneously enhancing their retention measures (NWRM) restoration was to increase water productivity divided in a short-term implementation (2003-2005), retention and restore wetland habitats for the two important bird medium term (2006-2010) and long term (2011-2033). The project species and increase the overall biodiversity. The hydraulic works has undertaken a highly intensive eradication of the mimosa tree. included creation of a retention area to secure water in the upper The project has generated employment opportunities for at least basin. Planting of wetland species aimed to have maximum effect 150 people from local communities. on the biodiversity. The project was funded by the European Union, with support the Life+ project. Benefits Photo by Dimitris Vetsikas on Pixabay Photo by Alphart Lungu on Flickr Employment, Wildlife, Ecotourism, Food. Benefits Source Biodiversity, Water Quality, Flood Reduction, Recreation. WWF Zambia, Government of Zambia Source https://www.wwfzm.panda.org/climate___energy_footer/?27825/ BirdLife Cyprus, Game Fund Department, Oroklini Community Wetlands-for-Sustainable-Cities Board, Department of Environment. Partnership for Co-funded Rise of public Large-scale Considered the Community protection and by external awareness and http://nwrm.eu/sites/default/files/case_studies_ressources/cs-cy- partnership lifeline of region involvement in conservation sources environmental 01-final_version.pdf for restoration economy maintenance approach education http://www.orokliniproject.org/en/home efforts and job generation 164 165 REFERENCES Aerts, J.C. 2018. A review of cost estimates for flood adaptation. Water, 10(11)1646. TEEB. 2011). The Economics of Ecosystems and Biodiversity in National and International Policy Making. Edited by Patrick Ayres, A., Gerdes, H., Goeller, B., Lago, M., Catalinas, M., García Cantón, Á., Brouwer, R., Sheremet, O., Vermaat, J., ten Brink. Earthscan: London and Washington. Angelopoulos, N., and Cowx, I. 2014. Inventory of river restoration measures: effects, costs and benefits. Restoring rivers FOR effective catchment management (REFORM). United States Environmental Protection Agency (U.S. EPA). 2002. Functions and Values of Wetlands. EPA 843-F-01-002c. https://nepis.epa.gov/Exe/ZyPDF.cgi/200053Q1.PDF?Dockey=200053Q1.PDF Barbier, E.B., Acreman, M., and Knowler, D. 1997. Economic valuation of wetlands: a guide for policy makers and planners. Gland: Ramsar Convention Bureau. Urban Wetlands. Compendium Guide in the Partners for Resilience. https://www.wetlands.org/publications/urban- wetlands-compendium-guide-in-the-partners-for-resilience/ Bastian, R.K. and Benforado, J. 1988. "Water quality functions of wetlands: natural and managed systems". In The ecology and management of wetlands. 87–97. Springer, New York, NY. Van der Duim, V.R., and Henkens, R.J.H.G. 2007. Wetlands, poverty reduction and sustainable tourism development: opportunities and constraints. Wetlands International. Wageningen University & Research. Chabwela, H. and Haller, T. 2010. Governance issues, potentials and failures of participative collective action in the Kafue Flats, Zambia. International Journal of the Commons, 4(2). Valach, A.C., Kasak, K., Hemes, K.S., Anthony, T.L., Dronova, I., Taddeo, S., Silver, W.L., Szutu, D., Verfaillie, J., and Baldocchi, D.D. 2021. Productive wetlands restored for carbon sequestration quickly become net CO2 sinks with site- Christianson, L., Tyndall, J.C., Helmers, M. 2013. Financial Comparison of Seven Nitrate Reduction Strategies for level factors driving uptake variability. PLoS ONE 16(3): e0248398. https://doi.org/10.1371/journal.pone.0248398 Midwestern Agricultural Drainage. Water Resources & Economics. http://dx.doi.org/10.1016/j.wre.2013.09.001 Wood, A.P. and van Halsema, G.E. 2008. Scoping agriculture–wetland interactions: Towards a sustainable multiple- Convention on biological diversity. 2015. Wetlands and Ecosystem Services. response strategy (Vol. 33). Food and Agriculture Organization of the United Nations. https://dev-chm.cbd.int/waters/doc/wwd2015/wwd-2015-press-briefs-en.pdf Covington, P., Gray, R., Hoag, C., Mattinson, M., Tidwell, M., Rodrigue, P., and Whited, M. 2003. Wetland Restoration, Enhancement, and Management. https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs143_010838.pdf Faber-Langendoen, D., Kudray, G., Nordman, C., Sneddon, L., Vance, L., Byers, E., Rocchio, J., Gawler, S., Kittel, G., and Maltby, E. 1986. Waterlogged Wealth. Earthscan. International Institute for Environment and Development, London. LeRoy, H., Hellerstein, D., Ribaudo, M., Williamson,J., Nulph,D., Loesch,C., and Crumpton, W. Targeting Investments To Cost Effectively Restore and Protect Wetland Ecosystems: Some Economic Insights, ERR-183, U.S. Department of Agriculture, Economic Research Service, February 2015. Menard,S. and Comer, P. 2008. Ecological performance standards for wetland mitigation: an approach based on ecological integrity assessments. NatureServe. Arlington, Virginia https://www.natureserve.org/sites/default/files/projects/files/epa-ecolstdrds-wetlandmitigation_appendices.pdf McEldowney, S., Hardman, D.J., and Waite, S. 1993. Pollution: ecology and biotreatment. Longman Scientific & Technical. Mitsch, W.J., Bernal, B., Nahlik, A.M., Mander, Ü., Zhang, L., Anderson, C.J., Jørgensen, S.E., and Brix, H. 2013. Wetlands, carbon, and climate change. Landscape Ecology, 28(4)583–97. National Oceanic and Atmospheric Administration, Environmental Protection Agency, Army Corps of Engineers, Fish and Wildlife Service, and Natural Resources Conservation Service. 2003. An Introduction and User's Guide to Wetland Restoration, Creation and Enhancement. http://jordanrivercommission.com/wp-content/uploads/2011/04/restdocfinal.pdf Ozment, S., Gretchen, E., and Jongman, B. 2019. Nature-Based Solutions for Disaster Risk Management. Washington, D.C. World Bank Group. http://documents.worldbank.org/curated/en/253401551126252092/Booklet Plastina, A. and A. Johanns. 2016. Iowa farm custom rate survey. Ag Decision Maker. File A3-10; FM 1698 (Revised, March 2016). Ramsar Convention Secretariat, 2018. Ramsar Briefing Note 10. https://www.ramsar.org/sites/default/files/documents/ library/bn10_restoration_climate_change_e.pdf Roggeri, H. 2013. Tropical freshwater wetlands: a guide to current knowledge and sustainable management (Vol. 112). Springer Science & Business Media. Streever, W.J. 1997. Trends in Australian wetland rehabilitation. Wetlands Ecology and Management, 5(1)5–18. 166 167 FACTS AND FIGURES DESCRIPTION Similar to natural inland wetlands in appearance, constructed inland wetlands are engineered systems that have been designed and constructed to utilize the natural processes involving wetland vegetation, soils and their associated microbial assemblages to assist in treating wastewater and to provide other supplementary functions. In urban regions, constructed inland wetlands can help offset the negative anthropogenic effects on the environment, sequester carbon, and help cities adapt to climate change. They can also help reduce organic, inorganic, and excess nutrient contaminants in surface and groundwater, municipal wastewater, industrial wastewater, domestic sewage, and other polluting sources. In arid climates and other areas with water shortages, constructed inland wetlands can also provide great value by cleaning and allowing the reuse of water, recharging the aquifers, and directly contributing to the conservation of natural resources. Constructed inland wetlands also offer scenic, recreational, educational, psychological, and economic value to the communities and a habitat for a great variety of species. Constructed inland wetlands range in size and appearance with free surface water flow and subsurface flow wetlands being the most common types. As part of a green infrastructure network of a city, these wetlands contribute to the protection of urban areas from floods and help maintain water quality in ponds and rivers as well as engineered gray water recycling systems in buildings and neighborhoods. TYPE OF CITY SCALE APPROACH Neighborhood Rehabilitate, Restore, Enhance Convert existing green spaces into constructed Coastal Delta wetlands. City Create River basin Construct new inland wetlands. River Mountain PROCESSES Carbon sequestration Evapotranspiration Cooling effect Biodiversity Water collection CONSTRUCTED INLAND WETLANDS Overflow Infiltration Water cleaning Sediment trapping Clean recharge Urban Wetlands Park, Nugegoda, Sri Lanka Photo by Shruthimathews on Flickr 168 169 VISUALIZATIONS VISUALIZATION OF CONSTRUCTED INLAND WETLANDS IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR CONSTRUCTED INLAND WETLANDS Surface constructed wetlands Free water surface constructed wetlands clean water through a series of planted marshes and engineered soils that remove contaminants. They imitate a natural wetland ecosystem where plants filter water. 1 Wetland plants are a great natural asset; in addition to purifying water, they often support high levels of biodiversity (Kennen and Kirkwood 2015). 3 2 Subsurface gravel wetlands Horizontal subsurface-flow constructed wetlands treat contaminated water by pumping it slowly through the subsurface gravel beds where it gets filtered through the root zone and the soil in a vertical or horizontal flow pattern. Subsurface wetlands offer the advantage of space efficiency and the ability to prevent mosquito breeding (Kennen and Kirkwood 2015). Details of increased benefits for the urban living environment 1 2 3 Floating wetlands Constructed floating wetlands have plants installed on floating structures that are placed in existing water bodies to filter contaminants. Existing contaminated water bodies, urban rivers, canals, and ponds may be treated with floating wetlands. Secondary benefits include water cooling and habitat for wildlife (Kennen and Kirkwood 2015). Constructed inland wetlands Constructed inland wetlands create Constructed inland wetlands deliver become recreational an opportunity to raise community aesthetic and sensory experiences destinations in the city, awareness and involvement in water for urban communities. transforming neighborhoods and climate related challenges. and adding diversity to green spaces. 170 171 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of constructed inland wetlands. The diagram in this section shows a sampling of important benefits that constructed inland wetlands can provide to people. Water quality and sediment management Pluvial flood risk reduction Pluvial flood regulation Heat stress risk reduction Biodiversity CONSTRUCTED Subsidence Heat INLAND regulation regulation WETLANDS Tourism and recreation Drought regulation Water pollution regulation Carbon storage and Human health sequestration Pluvial flood regulation: Constructed inland wetlands reduce the amount of stormwater runoff by collecting and storing water Pluvial flood risk reduction: Constructed inland wetlands collect Human health: Strong evidence supports that access to water during flood events. Attenuation capacity of constructed wetlands is determined almost entirely by the size and shape of the basin urban stormwater runoff during storm events. While their flood bodies has positive mental health benefits (Volker and Kistemann and the controls used to manage outflow during flood events (Ozment et al. 2019). attenuation benefits may vary, they typically include a flood 2015). Visiting rivers, lakes and streams increases happiness bypass channel to prevent damage to the wetland during major (Helliwell et al. 2020). Urban wildlife, particularly birds improve Heat regulation: Open water surfaces of constructed inland wetlands have the capacity to absorb heat and help regulate the rate of flood events. As such, their flood mitigation potential is typically the overall effect of green space, provide calming effect, and air temperature change. Open water and wetlands reflect solar radiation and influence humidity and microclimates through natural most optimal for small flood events. help relief stress (Ulrich 2002). In the urban context, constructed processes. Similar to natural wetlands, these conclusions can be drawn from a study conducted in Mexico City that measured the Heat stress risk reduction: Constructed inland wetlands can inland wetlands support physical health and psychological effect of wetlands on temperature and recorded an incremental rise of about 2°C (35.6°F) every 35 meters as the distance from contribute to reduce the heat island effect in urban areas. wellbeing. the body of water increased (Wetlands International 2020). In addition, a study of a large industrial wetland in the Middle East This is because constructed wetlands are dominated by open Biodiversity: The water-based natural habitat associated with demonstrated a reduction in temperature of 10°C (50°F) between the center and the perimeter of the wetland in a one-kilometer waters that reflect sunlight at low angles and take much longer constructed inland wetlands attracts wildlife species and can distance (Stefanakis 2019). to absorb heat from solar radiation than paved or built areas. support the creation of healthy multifunctional landscapes, This ability to maintain lower temperatures allows wetlands to connected to the larger landscape mosaic. In larger wetlands, Other functions: Constructed inland wetlands are typically designed to address water quality risks by removing various pollutants provide cooling for the surrounding areas, which is significantly biodiversity values and habitat variability can be enhanced by (Kennen and Kirkwood 2015). They can clean stormwater, wastewater, and groundwater by removing and—partially or completely— relevant in urban environments where heat stress is more introducing islands and creating areas of varying water depth. degrading organic contaminants and nitrogen, while filtering out and storing other inorganic contaminants in the soil (Kennen and critical (Wetlands International 2020). As a strong source of biodiversity, constructed inland wetlands Kirkwood 2015). Tourism and recreation: Constructed wetlands are designed to can positively change the character and identity of the urban imitate and perform the functions of natural wetlands. They act environment (Stefanakis 2019). as aesthetically pleasant urban green spaces, which contribute Water quality and sediment management: Constructed to the wellbeing of the residents and provide opportunities wetlands transform or remove various organic and trace for recreational activities. They also invite residents to get element and nutrient pollutants through a series of physical, involved in outdoor activities, such as bird watching and sports biological, and chemical processes, and improve the water (Stefanakis 2019). quality. Although efficiency of removal can vary considerably, Carbon storage and sequestration: As with natural inland constructed wetlands may be highly effective in addressing water wetlands, constructed wetlands can also play an important quality risks (Stefanakis 2019). While constructed wetlands role in carbon sequestration. Performance does however can trap sediments, this may undermine other functions and depend on design, and if not managed and designed properly, sediment traps are often included in the designs, requiring constructed wetlands could become a source rather than a sink regular maintenance. of greenhouse gases (Rosli et al. 2017). 172 173 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: Constructed inland wetlands are well-suited nature-based solutions for stormwater Substrate: Constructed inland wetlands include soil or gravel-based horizontal flow systems. Depending on management and water reuse in tropical and temperate regions (Stefanakis 2020). In colder regions the type of soil, such systems may require a ground liner that helps maintain saturation levels and prevents however, low temperatures reduce physical and biological activity and reduce purification capacity of contamination of the groundwater. They serve as a sink for pollutants and have a high water-holding wetland plants. As such, constructed wetlands, installed to clean wastewater in cold climates, require capacity. They also facilitate plant growth and propagation and may hinder the growth of undesirable extra technical measures to maintain their performance, as seasonal variations in performance may occur species (DEP 2006). (Maehlum et al. 1995). Mosquitoes: Mosquitoes are not uncommon in constructed inland wetlands, however it is possible to Hydrology: Maintaining appropriate hydrological regimes—including appropriate levels of soil saturation reduce mosquito infestation and larvae development by creating continuous water flow, shaded water and inundation—is critical for the proper functioning of a constructed inland wetland. This includes surface, and abundance of local fauna that eat mosquitoes. Avoiding stagnant backwaters is particularly avoiding highly variable flows that can flush the system and undermine treatment functions. The distance important to reduce mosquito levels (EPA 1995). to the groundwater table is not a major constraint because a high water table can help maintain wetland conditions (DDOE 2012). However, wetlands designed to treat domestic and agricultural wastewater require lining to avoid any contamination of the groundwater (EPA 1995). URBAN Soil: Soils underlying the proposed inland wetland should have the right infiltration rates and other subsurface properties. Highly permeable soils will make it difficult to maintain appropriate patterns of saturation and inundation to maintain wetland habitat and associated treatment functions. If adequate Land use: Urban parks and green areas in residential, commercial, or industrial areas as well as major soils are not available, artificial liners should be installed to facilitate better performance (DDOE 2012). infrastructure networks are suitable land uses for constructed wetlands. Soil tests can be conducted to determine the soil characteristics. Water quality: The effectiveness of constructed inland wetlands in assimilating pollutants primarily Urban density: Suitable urban density for constructed wetlands areas ranges from low to medium. depends on the quality of inflowing water and wetland size in proportion to the catchment area. As such, the design of constructed wetlands should be informed by a sound understanding of expected inflow volumes and water quality characteristics. Area: Small to medium. Constructed wetlands are nature-based solutions typically designed for application TECHNICAL at a neighborhood and city scale. Integrated urban planning: Constructed wetlands can be integrated with green public areas, public parks, Slope: While constructed inland wetlands can be built almost anywhere; a site with gradual slopes that and stormwater drainage systems. They can be installed as part of the sewerage upgrade and system can be easily altered to collect and hold water will simplify the design and construction, and minimize the capacity expansion. costs (EPA 1995). The wetland, including the longitudinal slope, must then be designed in such a manner that water retention time is optimized to allow for effective treatment. Dimensions: Constructed wetlands are normally designed to occupy between 2% and 5% of the MAINTENANCE contributing drainage area depending on the nature of water to be treated. The design, dimensions and the layout of different wetland zones should be site and context specific but typically include: an inlet zone for removal of course sediments; a macrophyte zone for removal of fine particles and uptake of soluble For the first two years following the installation, constructed inland wetlands should be inspected at least four times a year, nutrients; a macrophyte outlet zone that channels stormwater into adjoining downstream structures; especially after major storms. Wetland and buffer vegetation may require support during the first three years and undesirable and a high flow bypass channel to protect the wetland from potentially damaging abnormally high flow. species should be removed. Once established, constructed wetlands should require relatively little maintenance (DEP 2006) although regular removal of litter and sediment may be necessary in some contexts. Planting and growing strategy: Vegetation is an integral part of the wetland system. It reduces stormwater flow velocities, promotes sediment settling, provides growth surfaces for beneficial microbes, and absorbs pollutants. Constructed wetlands should have several different zones of vegetation with robust, noninvasive, fast growing perennial plants (DEP 2006). 174 175 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land is Costs associated with wetland Long-term maintenance costs of required for constructed inland construction are site-specific and will constructed inland wetlands are site- wetlands. vary according to site conditions, soil specific and may include activities characteristics, hydrology, and design such as buffer mowing, replacing Land on which constructed inland specifics. gates and other control structures, wetlands may be located could be ensuring a continuous supply of public or private. Inland wetland construction cost water, and invasive species removal. components include planning Land area required for constructed and design, engineering, project inland wetland areas will vary from preparation, soil excavation, and smaller to larger areas, raising planting. Constructed wetlands are transaction costs if engagement usually less expensive than gray and collaboration with multiple infrastructure options for the same landowners and stakeholders is function (Ozment et al. 2019). necessary. Example land-related costs: • Acquisition costs • Land use (e.g., payments to landowners) costs • Land protection costs, including managing and controlling access • Community resettlement costs UNIT COST EXAMPLES THROUGHOUT THE GLOBE • First year costs in the US (Iowa) of a constructed • Replacing control structure gates is estimated wetland: US$10,000/acre (US$24,700/ha). to cost US$15/wetland acre (US$37/ha) in the • The cost of constructed wetlands in the Mid- US (Iowa) and be required every eight years. Atlantic region of the US ranges from US$34– (Christianson et al. 2013). US$40/m3 of detention volume (EPA 1995). • Maintenance cost of constructed wetlands have • Buffer mowing is estimated to cost US$3/ been estimated at US$0.1/m2/ year (US$1,000/ wetland acre (US$7.41/ha) in the US (Iowa) ha/year) of wetland surface area in the UK (Aerts (Plastina and Johanns 2016). 2018). Oslo, Norway Photo by L. Ulrich. Licensed under Creative Commons 176 177 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned about constructed inland wetlands, drawn from a range of case studies from across the globe. Project #1: Tanner Springs Park, 2009–12 Project #3: Chattanooga Renaissance Park, 2005–13 Location: Portland, USA Location: Tennessee, USA Description: Located in Portland, Oregon, the celebrated Tanner Description: Completed in 2006, Renaissance Park has been a Springs Park is centered around a bioengineered wetland. The catalyst for reinvestment in Chattanooga’s growing Northshore project captures and filters stormwater from every roof and paved neighborhood ever since. The park is an environmentally focused surface in the surrounding area, reduces flooding during extreme brownfield redevelopment project that successfully demonstrates precipitation events, improves water and air quality. This high how a once-polluted area can be restored to a natural park setting performance constructed wetland of one acre boasts a great deal within an urban-driven landscape. A created wetland system now of biodiversity and offers a pleasant, accessible social hangout for collects and cleans runoff before release into the Tennessee River the neighborhood and delivers significant social benefits for the and is the centerpiece of the park that now serves as an amenity for community. The park also features a boardwalk, an art installation, adjacent new residential and mixed use developments. and a recreational path running through its central area. Park programming emerged through a series of participatory charrettes Benefits with the community, which built a strong sense of pride and Environmental, Biodiversity, Education, Heat Stress Risk Reduction. Photo by Cord Rodefeld on Flickr ownership among the participants. Photo by Michael Miller on Flickr Source Hargreaves Associates Benefits https://www.landscapeperformance.org/case-study-briefs/ Health, Education, Heat Stress Risk Reduction. renaissance-park Source Atelier Dreiseitl https://www.landscapeperformance.org/sites/default/files/ Climate Public space Participatory Brownfield Stimulate Water cleaning https://sustainability.asu.edu/urbanresilience/2018/11/portland- Renaissance%20Park%20Methodology_0.pdf awareness and renewal process with restoration neighborhood process as identity program local oregon-tanner-springs-park/ reinvestment design element communities of park design Project #2: Chulalongkorn Centenary Park, 2012–17 Project #4: Usaquén Urban Wetland, Completed 2016 Location: Bangkok, Thailand Location: Bogotá, Colombia Description: The Chulalongkorn University Centenary Park is Description: The 8,500 m2 landscape project, completed in 2016, the critical first part of Bangkok’s green infrastructure designed aims to transform and revitalize an emblematic public space in to mitigate environmental degradation and add much-needed northeastern Bogotá. Its design concept is based on the wetlands outdoor public space to the gray city. The park water treatment of the Bogota Savannah, a neighboring rocky area, and the system is built around constructed wetlands with detention lawns typical plant species. The project recreates the geometry of the and retention ponds. The constructed wetlands follow the slope of half aquatic, half terrestrial ecosystem, its colors, and textures. an inclined plane, and steps down through a series of weirs and A rainwater garden in the main square uses recycled water and ponds. Water passes through a weir, cascades down, flows through creates a native urban wetland that blends with its surroundings, a plant- filled pond below, passes through another weir, and flows the Andean hill backdrop, and preserves the native vegetation in its through another pond. Water is cleaned every time it passes natural habitat. Despite the seemingly wild, natural, and free-form through plants until reaching the retention pond, where children aspects of the urban design, a clear, rationalized structure and and adults can safely play and enjoy the water. construction style underlies the spatial composition. Photo by Landprocess / Panoramic studio Photo by Daniel Segura / OBRAESTUDIO Benefits Benefits Pollutants Reduction, Biodiversity, Tourism, Social Interaction. Education, Health, Economy, Heat Stress Risk Reduction. Source Source LandProcess, Kotchakorn Voraakhom Obraestudio www.nparks.gov.sg/-/media/cuge/ebook/citygreen/cg16/cg16_05. https://architectures.jidipi.com/a139012/usaquen-urban-wetland/ Urban icon Design oriented: Integrated in Public space Design oriented: Water cleaning pdf Launched as an educational renewal Launched as an and water international idea and cultural program idea competition reuse as social https://worldlandscapearchitect.com/chulalongkorn-centenary- interaction competition institution park-green-infrastructure-for-the-city-of-bangkok/#.YWV7s_lBxPY catalyst 178 179 REFERENCES Aerts, J.C. 2018. A review of cost estimates for flood adaptation. Water, 10(11)1646. Christianson, L., Tyndall, J.C., Helmers, M. 2013. Financial Comparison of Seven Nitrate Reduction Strategies for Midwestern Agricultural Drainage. Water Resources & Economics. http://dx.doi.org/10.1016/j.wre.2013.09.001 Dept. of Environmental Protection. 2006. Stormwater Best Management Practices (BMP) Manual. Pennsylvania. https://pecpa.org/wp-content/uploads/Stormwater-BMP-Manual.pdf District Dept. of the Environment. 2012. Stormwater Management. Guidebook. Watershed Protection Division. District of Columbia. https://nacto.org/docs/usdg/stormwater_management_guide_district_columbia.pdf Helliwell, J.F., Huang, H., Wang, S., and Norton, M. 2020. Statistical Appendix for Chapter 2 of World Happiness Report 2020. New York. Sustainable Development Solutions Network. Kennen, K. and Kirkwood, N. 2015. Phyto: Principles and resources for site remediation and landscape design. Routledge. Maehlum, T., Jenssen, P.D., and Warner, W.S. 1995. Cold-climate constructed wetlands. Water Science and Technology, 32(3)95–101. Plastina, A. and A. Johanns. 2016. Iowa farm custom rate survey. Ag Decision Maker. File A3-10; FM 1698 (Revised, March 2016). Ozment, S., Gretchen E., and Brenden J. 2019. Nature-Based Solutions for Disaster Risk Management. Washington, D.C.: World Bank Group. http://documents.worldbank.org/curated/en/253401551126252092/Booklet Rosli, F.A., Lee, K.FE., Goh, C.T., Mokhtar, M., Latif, M.T., Goh, T.L., and Simon, N. 2017. The Use of Constructed Wetlands in Sequestrating Carbon: An Overview. Nature Environment and Pollution Technology, 16(3) 813–819. Stefanakis, A.I. 2019. The role of constructed wetlands as green infrastructure for sustainable urban water management. Sustainability, 11(24)6981. Stefanakis, A.I. 2020. Constructed wetlands for sustainable wastewater treatment in hot and arid climates: opportunities, challenges and case studies in the Middle East. Water, 12(6)1665. Ulrich, R.S. 2002, April. Health benefits of gardens in hospitals. In Paper for conference, Plants for People International Exhibition Floriade Vol. 17(5) 2010. US Environmental Protection Agency. 1995. A Handbook of Constructed Wetlands. US EPA. https://www.epa.gov/sites/ production/files/2015-10/documents/constructed-wetlands-handbook.pdf Völker, S. and Kistemann, T. 2015. Developing the urban blue: comparative health responses to blue and green urban open spaces in Germany. Health & Place, 35:196–205. Wetlands International. 2020. Urban Wetlands. Compendium Guide in the Partners for Resilience. https://www.wetlands. org/publications/urban-wetlands-compendium-guide-in-the-partners-for-resilience/ White heron Photo by Rachel On Unsplash 180 181 FACTS AND FIGURES DESCRIPTION For centuries people settled along rivers, and used floodplains for agricultural purposes. As development continued, the incidence of flooding increased in urban areas leading to growing concerns around flood risk management. The traditional response was interfering with natural floodplain dynamics by building levees to contain water and sediment flows, or by straightening and dredging rivers to move water more quickly beyond flood prone areas. While these techniques reduce local flood risks, they can also exacerbate downstream flooding effects, and sometimes, create an artificial sense of security that encourages more development in floodplains. Climate change and a better understanding of these effects, has resulted in communities to demand sustainable, multifunctional and flexible solutions. In response, cities worldwide are investing in river and floodplain restoration projects that address flood risks while also improving waterfronts and creating multifunctional spaces that can be enjoyed by residents. This new paradigm, often known as “Room for the River,” focuses on enhancing the space available for rivers to be able to safely process higher water levels. While these projects are typically directed at addressing flood risk, rehabilitation actions are also designed to deliver additional environmental and social benefits including providing, increased biodiversity, additional habitat for wildlife, space for play, recreation, and sports. TYPE OF CITY SCALE APPROACH Neighborhood Protect Prevent encroachment and incompatible use of Coastal Delta floodplains. Preserve existing tree structure. City Rehabilitate, Restore, Enhance Reinstate more natural floodplain dynamics. Enhance flood attenuation capacity. River basin River Mountain Invest in recreational and other social benefits. PROCESSES Cooling effect Carbon sequestration Cleaning Water buffer Biodiversity RIVER FLOODPLAINS Sediment trapping Infiltration Groundwater Upper Serangoon Crescent, Singapore recharge Photo by Z on Unsplash 182 183 VISUALIZATIONS VISUALIZATION OF RIVER FLOODPLAINS IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR RIVER FLOODPLAINS Setting levees back 1 Levee setback is the process of relocating a levee further back in 3 the floodplain to provide extra space for the river to flood. Levee setback provides the river with more floodplain area to interact with and can result in lower flood elevation. The new space for the river allows new ecological and recreational activities (IDNR n.d.), and provides a greater diversity of floodplain habitats (Ayres et al. 2014). 2 River bypass or Oxbow An oxbow is a historical river meander that is cut off from the main channel during the natural process of channel migration, or through man-made channelization. Water levels are maintained through larger flooding events overflowing into the oxbow and groundwater seepage. Based on the habitat proposed, inlet and outlet structures may need to be constructed to regulate the inflow and outflow of water for the oxbow (IDNR n.d.). Details of increased benefits for the urban living environment 1 2 3 Re-activating the floodplain In incised floodplains, a new meandering stream channel is excavated on the original floodplain by raising the stream bed elevation. The former incised channel is then filled, converting it to a floodplain feature. This approach is used in areas where there are few lateral constraints and where flooding on the adjacent land can be increased. Floodplains can serve to Rehabilitation efforts that reconnect Rehabilitated floodplains can intercept and treat polluted the river to the floodplain can provide highly attractive runoff, capturing sediment and enhance attenuation and provide a landscapes and active riverfronts reducing pollution risks for diversity of habitats for wildlife. that attract investment and provide downstream communities. a range of opportunities for cultural and recreational activities. 184 185 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of river floodplains. The diagram in this section shows a sampling of important benefits that river floodplains can provide to people. Riverine flood Water quality and regulation sediment management Riverine flood risk reduction Heat stress risk reduction Resources Biodiversity Bank erosion production regulation RIVER FLOODPLAINS Heat regulation Water pollution regulation Tourism and recreation Air pollution Biodiversity regulation Carbon storage and sequestration Soil pollution regulation Riverine flood regulation: River floodplains reduce peak flows and downstream flooding by storing and slowly conveying water Riverine flood risk reduction: Floodplains are the first defense uniquely rich recreational context (Tockner and Stanford 2002). that overtop riverbanks during flood events (Ozment et al. 2019). In the event of a flood, a floodplain provides more space for the against flood damage when rivers overflow their banks, acting These values can be enhanced through targeted investments in water. Floodplain vegetation reduces the speed of surface water flow, and floodplain topography controls the direction of surface as a protective buffer for adjacent property and reducing recreational, cultural, and educational infrastructure. water flow and manages the amount of sediment being transported by the water. Restoration actions on floodplains aim to provide the damage to vital infrastructure in urban environments. Carbon storage and sequestration: Floodplains can store large enhanced flood capacity through the creation of flood bypasses, removal or rebuilding of the embankments at a different location, Floodplains store the water overflow from the river during a amounts of organic carbon in soils through overbank deposition restoration of the riverine vegetation, and excavation of the floodplain (Dige et at. 2017). flood and slowly release the water back. of sediments originating from catchment erosion processes. For Heat stress risk reduction: Urban rivers and floodplains have a example, an empirical study from California (USA) found a soil Heat regulation: Rivers and floodplains mitigate urban heat. Riparian and floodplain forests control river temperature preserving cooling effect on the surrounding areas. The degree of cooling carbon density of 2 tons CO2 per ha in the upper 2 meters of soils aquatic flora and fauna. Ota River in Japan, for example, cools the temperature by up to 5°C (41°F) directly above the river with is based on the ambient air temperature, seasonal water level (Steger et al. 2019). In terms of rates of sequestration, a study cooling effects extending 100 meters on both sides of the river (Hathway and Sharples 2012; Murakawa et al. 1991). variations and water temperature, solar radiation and the focusing on six rivers in southern England found sequestration water albedo, wind speed, and relative humidity. Riparian and rates of 69.2-114.3 g/m2 (Walling et al. 2006), but these estimates Other functions: Floodplain restoration improves water quality and reduces environmental pollution, facilitates sediment transport floodplain forests reduce and stabilize the temperature along can vary strongly by river basins and habitat types established in and storage, and mitigates soil erosion (Dige et at. 2017). Restored floodplains give room for seasonal water fluctuations, changes in the river, while the built environment reduces and dissipates floodplain areas. meander patterns and other dynamic river processes and have a positive effect on aquatic biodiversity (Ahilan et al. 2018). the effect. Urban design for the waterfront areas should take Biodiversity: Floodplains are among the most biologically advantage of the cooling effect, and specify surfaces that will productive and diverse ecosystems on earth, providing a range not absorb too much heat. Opening of streets to the river for of microhabitats for different plant and animal species. Given the example, will reduce the air temperature, while a street shut continual deposition and retention of nutrient-rich sediments, off from the river will not gain any benefit for its microclimate they tend to be more productive than adjacent uplands and are (Hathway and Sharples 2012). critical for maintaining aquatic and riparian biodiversity (Tockner Resource production: In some cultures, floodplains are and Stanford 2002). They also form an integral part of river developed for extensive agriculture and provide a broad suite ecosystems and act as important conduits for wildlife movement. of natural resources for local communities. Care must however Water quality and sediment management: Reduction of the be taken to balance the benefits from cultivation with risks of velocity of the river flow allows suspended sediments to settle flooding and loss of other important benefits such as water in floodplain areas. This improves water quality, supports quality enhancement and biodiversity benefits. nutrient cycling, increases productivity, and improves fish Tourism and recreation: River floodplains are attractive habitats habitat. Floodplains can also reduce downstream pollution by for wildlife, birds and other animals. Combined with their scenic intercepting urban runoff and removing the sediment and value, opportunities for activities such as fishing, bird watching, pollution, before water is released into the river (Ozment et al. biking, hiking, walking, swimming, and kayaking, they make for a 2019). 186 187 SUITABILITY CONSIDERATIONS ENVIRONMENTAL URBAN Location and climate: Floodplains are defined topographically as relatively flat surfaces adjacent to river channels and occupy the area where water flows during floods. Floodplains are therefore found Land use: Floodplains should be reserved as natural open space. Activities should be limited or restricted everywhere that rivers flow but are most prominent near a mouth of a large river and river middle in floodplains that are occasionally flooded and used for only compatible activities. courses, where the river also carries large amounts of sediment. Hydrology: River floodplain characteristics are primarily determined by the water levels and the seasonal water discharge from upstream areas of a river. In the event of a flood, floodplains store water that Urban density: The suitable urban density for river floodplains is low to medium. overflows from the main river channel. Any interventions in a floodplain need to be carefully planned to ensure that measures are designed with a clear understanding of historic, present and future expected catchment hydrology and should include an evaluation of the impacts on local and broader flooding patterns. Flood modeling techniques help simulate these conditions and design interventions that meet multiple objectives. Area: Medium to Large: River floodplains range from those associated with smaller rivers and streams to large floodplains at a city scale. TECHNICAL Integrated urban planning: River floodplains are typically key structuring elements of cities and an integral component of open space networks and recreational areas. Slope: The slope and the shape of a floodplain are key attributes affecting its retention capacity. Shallow slopes reduce flow velocity and prolong retention time whereas steeper slopes allow the water to run off quicker. The presence of oxbows and depressions can further enhance storage capacity. Floodplain profile: In natural conditions, a floodplain profile is shaped by the actions of the river, MAINTENANCE frequency and strength of flood, and the volume and velocity of stormwater moving toward the river. While maintaining natural floodplain dynamics is desirable, this is often not achievable in an urban context —where emphasis of rehabilitation is often on reducing flood risks. Many floodplain rehabilitation efforts Riverbanks are subject to erosion during and immediately after construction. To maintain the health of the river, sediment thus aim to strike a balance between enhancing natural processes, such as re-activating the floodplain, that ended up in the watercourse during construction of the banks should be removed. Dredging of the riverbed or grading while also reducing flood risks. This may involve modifying the natural floodplain profile by artificially of its banks may be required to maintain design flow capacity (IDNR n.d.). Levees as well have to undergo maintenance and lowering it down or creating berms or levees to protect adjacent areas. checks every year and reinforcement at the long term (Min. of IWM 2021). Dimensions: Where possible, the extent of the original floodplain should be protected and retained, together with a buffer to allow climate change related adjustments to be made in future. Riverbanks: Floodplain restoration often includes reshaping river banks to prevent erosion and support natural vegetation. Such shaping should be accompanied by appropriate bank stabilization and revegetation measures, which typically include the use of an appropriate mix of seeds, and vegetation adapted to soil conditions and tolerant to periodic inundation. Planting and growing strategy: Floodplain restoration should support native plants—trees, shrubs, and grasses that can survive frequent or prolonged floods. If trees are selected, these should be chosen for their ability to withstand high water table conditions and tolerate the wet soils of the floodplain (DEP 2006). 188 189 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land River floodplain protection and River floodplain maintenance costs is required for river floodplain restoration costs will vary widely will vary according to location, protection and restoration. according to site conditions, location, hydrology, climatic conditions, and hydrology, restoration actions labor and material costs. Large Land on which river floodplains are required, planning, design and floods may also result in significant protected and/or restored may be engineering requirements and labor damage that can result in unexpected public or private. and material costs. maintenance costs. Land area required for river floodplain protection and/or restoration will be relatively large, raising transaction costs associated with avoiding development and protecting river floodplains if engagement and collaboration with multiple landowners and stakeholders is necessary. Example land-related costs: • Acquisition costs • Land use (e.g., payments to landowners) costs • Land protection costs, including managing and controlling access • Community resettlement costs UNIT COST EXAMPLES THROUGHOUT THE GLOBE • The cost of restoring and reconnecting • Dredging and river widening: US$2/m3 floodplains in Europe is estimated to range from (Bangladesh)–$59/m3 (United Kingdom) (Aerts US$10,000–US$800,000/ha (EEA 2017). 2018). • Floodplain restoration costs in Europe range • Reconnecting watercourses to their floodplains in from US$132–US$363,800/ha, with a median Europe: US$2,400–US$300,000/connection (Ayres unit cost of US$27,566/ha (Ayres et al. 2014). et al. 2014). • Removing levees along rivers in Europe: US$1– • Annual maintenance costs for floodplain projects 100/m3 (Ayres et al. 2014). are estimated at 0.5% to 1.5% of total investment • Introducing meanders in Europe: US$15– costs (Dige et al. 2017). US$1,000/m (Ayres et al. 2014). Trukhaniv Island, Kyiv, Ukraine Photo by Tanya Pro on Unsplash 190 191 NBS IN PRACTICE The four projects in this section highlight selected good practices of river floodplain projects around the globe. Project #1: Odra River Basin Flood Protection Project, 2007–20 Project #3: Rio Bogota Environmental Flood Control Project, Location: Wroclaw, Poland 2011–21 Description: Wroclaw, the largest city in western Poland, is at risk Location: Bogota, Colombia from river flooding. The Odra River Basin Flood Protection Project Description: The objective of the Rio Bogota Environmental is designed as passive flood prevention for the Odra River basin. Recuperation and Flood Control Project was to transform the The project is connected to a series of other projects that include Bogota River into an environmental asset for the Bogota Capital components to combine existing gray infrastructure with natural metropolitan region by improving the water quality, reducing flood features in the river basin. The project is a part of 1 billion euro risks, and creating multifunctional areas along the river. program, co-financed by the World Bank and the EU Cohesion Fund. The project rehabilitated eight areas—wetlands and meanders— It has increased the floodwater flow capacity from 2,200 m3/s up with a total area of approximately 175 hectares, which function to 3,600 m3/s and protects 2.5 million people against flooding in as flood detention areas, ecological habitats, and public several towns along its banks. spaces. The main strategies focused on reduction of flood risk and establishment of multifunctional zones along the river. Benefits Environmental improvement works included river dredging, Photo by Maxence Peniguet on Flickr Flood risk reduction, Economy, Health, Heat Stress Risk Reduction. Photo by CAR (Corporación Autónoma Regional de Cundinamarca) embankment construction, meanders and wetlands, and the Source construction of a recreational landscape. Government of Poland, World Bank, Aecom. Benefits https://documents.worldbank.org/en/publication/documents- Flood risk reduction, Recreation, Economy, Heat Stress Risk reports/documentdetail/320251467986305800/poland-odra- Reduction. Comprehensive Strengthen the Hybrid strategy vistula-flood-management-project Water as leverage Strengthening Creation of new Source flood protection institutional of NBS and gray to establish the capacity for urban park and World Bank strategy at city capacity to infrastructure partnership with the day-to-day city ecological https://projects.worldbank.org/en/projects-operations/project- level mitigate floods local governments implementation structure detail/P111479 Project #2: Yanweizhou Park in Jinhua City, Completed 2014 Project #4: Room for the River Programme, 2012–16 Location: Jinhua River, Jinhua, China Location: Nijmegen, The Netherlands Description: The Yanweizhou project used a cut-and-fill strategy Description: The Room for the River Programme in The Netherlands to balance earthwork by creating a water-resilient terraced river was developed to provide high water level protection for 4 million embankment covered with flood-adapted native vegetation. The people along the Waal River catchment areas. To mitigate rising terraced embankment remediates and filtrates the storm water water, an existing levee was relocated 350 meters inland. A channel from the pavement above. Although the design and strategies to cope with high water was excavated between the levee and employed address only a small section compared to the hundreds the river, leaving an island between the channel and the river. of kilometers of river embankment, the Yanweizhou Park project Relocation of the levees provided the river more room that resulted showcases a replicable and resilient ecological solution to large- in reduction to water level. In extreme floods, the water level scale flood management. The park has meandering vegetated reduces as much as 35 cm. The project increased spatial quality and terraces, curvilinear paths, a serpentine bridge, circular bioswales environmental benefits tremendously. The entire area became a and planting beds, and curved benches. The project has given the river park where nature and recreational activities now co-exist. city a new identity and an acclaimed poetic landscape. Photo by Kongjian Yu / Turenscape Photo by Richard Brunsveld on Unsplash Benefits Benefits Flood risk reduction, Health and Wellbeing, Economy, Recreation, Flood risk reduction, Identity, Health and Wellbeing, Heat Stress Risk Biodiversity. Reduction. Source Source Rijkswaterstaat (Dutch Ministry of Infrastructure and Water Kongjian Yu, Peking University and Turenscape Management) Environmental Creation of an Equitable Government Environmental Creation of stewardship for iconic new urban access and http://landezine.com/index.php/2015/03/a-resilient-landscape- implementation stewardship in new river https://www.un-ihe.org/sites/default/files/13270-rvdr-brochure- flood prevention park and reduction yanweizhou-park-in-jinhua-city-by-turenscape/ leadership working with waterfront and governance-engels_def-pdf-a.pdf through NBS recreation of urban water rather a new district https://www.dutchwatersector.com/news/room-for-the-river- amenities segregation than against it development programme 192 193 REFERENCES Ahilan, S., Guan, M., Sleigh, A., Wright, N., and Chang, H. 2018. The influence of floodplain restoration on flow and sediment dynamics in an urban river. Journal of Flood Risk Management, 11: S986–S1001. Aerts, J.C., 2018. A review of cost estimates for flood adaptation. Water, 10(11)1646. Ayres, A., Gerdes, H., Goeller, B., Lago, M., Catalinas, M., García Cantón, Á., Brouwer, R., Sheremet, O., Vermaat, J., Angelopoulos, N., and Cowx, I. 2014. Inventory of river restoration measures: effects, costs and benefits. Restoring rivers FOR effective catchment management (REFORM). Dept. of Environmental Protection. 2006. Pennsylvania Stormwater Best Management Practices (BMP) Manual. https://pecpa.org/wp-content/uploads/Stormwater-BMP-Manual.pdf Dige, G., Eichler, L., Vermeulen, J., Ferreira, A., Rademaekers, K., Adriaenssens, V., and Kolaszewska, D. 2017. Green Infrastructure and Flood Management: Promoting Cost-Efficient Flood Risk Reduction via Green Infrastructure Solutions. European Environment Agency (EEA) Report, (14). https://www.eea.europa.eu/publications/green-infrastructure-and-flood-management Dunne, T. and Leopold, L.B., 1978. Water in environmental planning. Macmillan. EEA (European Environmental Agency). 2017. “Green infrastructure and Flood Management: Promoting Cost-Efficient Flood Risk Reduction via Green infrastructure Solutions.” Copenhagen: European Environmental Agency. https://www. eea.europa.eu/publications/green-infrastructure-and-flood-management Hathway, E.A. and Sharples, S., 2012. The interaction of rivers and urban form in mitigating the Urban Heat Island effect: A UK case study. Building and Environment, 58:14–22. Ministry of Infrastructure and Water Management. 2018. The Dutch make Room for the River. Interview with Willem Jan Goossen. https://www.eea.europa.eu/signals/signals-2018-content-list/articles/interview-2014-the-dutch-make Murakawa, S., Sekine, T., Narita, K.I., and Nishina, D. 1991. Study of the effects of a river on the thermal environment in an urban area. Energy and Buildings, 16(3–4) 993–1001. Nardi, F., Annis, A., Di Baldassarre, G., Vivoni, E.R., and Grimaldi, S. 2019. GFPLAIN250m, a global high-resolution dataset of Earth’s floodplains. Scientific Data, 6(1)1–6. Natural Water Retention Measures. n.d. http://nwrm.eu/measure/floodplain-restoration-and-management NetMap. n.d. Floodplain Classes. http://www.netmaptools.org/Pages/NetMap_Portal_Help/floodplain_classes.htm Ozment, S., Gretchen, E., and Jongman, B. 2019. Nature-Based Solutions for Disaster Risk Management. Washington, D.C. World Bank Group. http://documents.worldbank.org/curated/en/253401551126252092/Booklet River Restoration Toolbox Practice - Iowa Department. Rosgen, D.L. and Silvey, H.L. 1996. Applied River Morphology, 1481. Pagosa Springs, CO: Wildland Hydrology. Schindler, S., Sebesvari, Z., Damm, C., Euller, K., Mauerhofer, V., Schneidergruber, A., Biró, M., Essl, F., Kanka, R., Lauwaars, S.G., and Schulz-Zunkel, C. 2014. Multifunctionality of floodplain landscapes: Relating management options to ecosystem services. Landscape Ecology, 29(2), 229–44 Kristin Steger, K., Peter Fiener, P., Marvin-DiPasquale,M., Viers, J.H., and Smart, R.D. 2019. Human-induced and natural carbon storage in floodplains of the Central Valley of California. Sci Total Environ, 651(Pt 1):851–858. doi: 10.1016/j.scitotenv.2018.09.205. https://pubmed.ncbi.nlm.nih.gov/30253367/ Tockner, K. and Stanford, J.A. 2002. Riverine flood plains: present state and future trends. Environmental Conservation, 308–30. Walling, D.E., Fang, D., Nicholas, A.P., Sweet, R.J., Rowan, J.S., Duck, R.W., and Werritty, A. 2006. River flood plains as carbon sinks. IAHS Publication, 306:460. Tiszaszőlős, Hungary Photo by Dimitry Ljasuk On Unsplash 194 195 FACTS AND FIGURES DESCRIPTION Mangroves, also referred to as the blue forest, are a unique coastal ecosystem of halophytes — salt tolerant trees and shrubs that live in the coastal intertidal zone. About 80 different species of mangrove trees—red, white, and black mangroves—are found in many coastlines across tropical and subtropical latitudes near the Equator. They thrive in highly dynamics areas, such as deltas and coastal environments. In these coastlines, mangroves are often located close to urban environments and provide an important protective buffer from coastal hazards. Their flood protection benefits have been estimated more than $US65 billion per year globally (Menendez et al. 2020). Mangrove forests also help stabilize the coastline because they reduce erosion from storm surges, currents, waves, and tides. In addition to flood mitigation, mangrove forests also provide multiple economic and social benefits to coastal communities. Mangroves act as filters for nutrients and sediment, reduce erosion, maintain water quality, and offer feeding and breeding habitats for fish, birds, and crustaceans, critically contributing to the livelihoods of many fishing communities (Zu Ermgassen et al. 2020). Mangroves are also among the most carbon-rich forests in the tropics and one of the coastal ecosystems globally with the greatest potential to capture and store blue carbon (Taillardat et al. 2018). Mangroves are unusually robust and demonstrate marvels of natural adaptation and resilience. Despite their important services to people and their environmental values, mangroves have been disappearing at an alarming rate (Barbier et al. 2011). In the 1970s, mangroves may have covered as much as 200,000 square kilometers, or 75 percent of the world’s coastlines (Spalding et al. 2014). In the last 50 years, between 30 and 50% of mangroves have been lost globally and they continue to be lost at a rate of 2% each year (Valiela et al. 2001; Alongi 2002; FAO 2007). Major causes of destruction to mangrove ecosystems include deforestation, aquaculture expansion in coastal areas for shrimp farming, and aquaculture ponds (Barbier and Cox 2003), to freshwater diversion and land reclamation (Valiela et al. 2001) and other forms of unsustainable use of coastal resources and development. It has been estimated that 62% of global losses between 2000 and 2016 resulted from land use change, primarily through conversion to aquaculture and agriculture. Up to 80% of these human‐driven losses occurred within six Southeast Asian nations (Goldberg et al. 2020). However, there is great potential to restore many mangrove areas by planting seedlings in combination with restoration of hydrological flows (Wetland International, n.d.). TYPE OF CITY SCALE APPROACH Neighborhood Protect Conserve existing mangroves. Coastal Delta Rehabilitate, Restore, Enhance City Restore existing mangroves and enabling conditions for natural regeneration. River basin River Mountain PROCESSES Biodiversity Carbon sequestration Wave and surge reduction Cooling effect MANGROVE FORESTS Sediment trapping Fresh water balance Nusa Lembongan, Indonesia Photo by Joel Vodell on Unsplash 196 197 VISUALIZATIONS VISUALIZATION OF MANGROVE FORESTS IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR MANGROVE FORESTS Restore hydrology 3 Mangrove forests rely on the tides for their growth and expansion. 2 The strategic removal of certain water control devices will recover tidal influence and recreate the conditions for mangrove development, especially in areas were human activities previously restricted tidal environments. 1 Permeable structures Permeable structures help mangrove forest restoration by capturing sediment and providing substrate for mangroves to grow naturally. The permeable structures are placed as a grid system facing the direction of the tidal current to maximize the sediment capture and dampen erosive waves. The construction can be done by local communities with structures made of local materials such as bamboo, twigs, and other brushwood (Deltares n.d.). Details of increased benefits for the urban living environment 1 2 3 Planting or sowing Planting or sowing mangroves requires previous study of the area to ensure that biophysical conditions are appropriate for mangrove recovery. The purpose of the planting is to assist or enrich the natural regeneration process when natural supplies of seeds and propagules are limited due to lack of nearby parent trees or lack of hydrological connection to these trees. This is often the case along Shallow waters of mangrove Mangrove forests provide important Mangrove forests improve water coastlines that suffer widespread mangrove degradation (Deltares forests provide a sustainable benefits to communities that can quality to sustain life cycles of n.d.). mobility network for water leverage sustainable fishing and commercial and recreational transportation for local aquaculture for livelihoods or for fisheries. A complex, healthy communities. nature-based tourism opportunities. mangrove forest is also crucial for its flood mitigation performance. 198 199 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of mangrove forests. The diagram in this section shows a sampling of important benefits that mangrove forests can provide to people. Water quality and Coastal flood sediment management risk reduction Coastal flood regulation Resources Biodiversity production Salt intrusion MANGROVE regulation FORESTS Tourism and Sea level rise recreation adaptation Biodiversity Coastal erosion Carbon storage and regulation sequestration Coastal flood regulation: Mangrove forests act as natural barriers that mitigate wave action and lessen the effects of periodic storms Coastal flood risk reduction: Mangrove forests act as natural Carbon storage and sequestration: Like inland wetlands, and coastal flooding (Spalding et al. 2014; Alongi 2008). Their effectiveness and the magnitude of potential wave attenuation and barriers that protect coastal communities from periodic storm mangrove forests are a globally important carbon sink, with surge mitigation depends on the complexity of the mangrove forest that is determined by species composition, width, structure events and flooding. Mangrove forests reduce wave height and high soil and aboveground carbon densities that often exceed and density, stem and root diameters of trees, age and height, shore slope, bathymetry, incident waves, and the tidal stage at the velocity with their dense vegetation and stabilize coastlines by 1,000 tons CO2 per ha. For example, for Indonesian mangroves, time it encounters the forest (Hashim and Catherine 2013). Research demonstrates the effects of mangrove forest on coastal flood trapping sediment with their root systems and during heavy on average, carbon density is estimated at 1,083 tons CO2 per mitigation: rainfall or high flows in rivers (Bann 1998). Globally, they reduce ha (Mudiyarso et al. 2015). Mangrove restoration, particularly flood damages by more than $US 5 billion per year (Menendez involving the establishment of mangrove trees, is highly • Mangroves reduce wave heights by an average of 31% (95% CI: 25–37%) (Narayan et al. 2016; Spalding et al. 2014); et al. 2020). Some of the cities where most people are protected productive and results in high removal rates estimated at 23.1 • Modeling of natural mangroves suggest significant reduction in tsunami wave flow pressure in forests of at least 100 meters in by mangroves are in Vietnam, India, and Bangladesh. Many ton CO2 per ha per year during the first 20 years of growth and width (Alongi 2008); 20-kilometer coastal stretches, particularly those near cities, remaining high at 10.5 tons CO2 per ha per year, during the • Recorded water levels in southwestern Florida showed that mangroves lower flood water levels by around 93 mm/km from two receive more than $US250 million annually in flood protection lifetime of mangrove stands (Bernal et al. 2018). These rates hurricane events in 2004 and 2005 (Krauss et al. 2009); benefits. Mangroves have been estimated to protect 15 million exceed those for most natural forests. • The capability of a mangrove forest to dissipate wave energy depends on its specie composition. The Rhizophora spp. and people per year from flooding, especially in Vietnam, India and Biodiversity: Mangrove forests support the conservation of Pandanus odoratissimus are most effective in wave attenuation due to their complex aerial root structure that creates greater Bangladesh (Menendez et al 2020). biological diversity by providing habitats, spawning grounds, friction for the incoming waves (Hashim and Catherine 2013). Resource production: Mangrove forests are among the world’s nurseries, and nutrients for many animals. These include several most productive fishing grounds, yielding vast numbers of fish, endangered species: crocodiles, iguanas, the Royal Bengal Other functions: Mangroves forests mitigate salt intrusion, coastal erosion, sea level rise depending on sedimentation or accretion crabs, shrimps, and mollusks. Globally, more than 4 million tiger, otters, manatees, dolphins, and birds like herons, egrets, rates of specific areas, and offset the loss of biodiversity in urban environments (Bann 1998). artisanal fishers rely on mangroves (Zu Ermgassen et al. 2020). pelicans, and eagles. Mangroves also help protect offshore Mangroves also provide a sustainable supply of forest products, features such as coral reefs, seagrass beds, and shipping lanes including wood products such as round wood, poles, fuel by entrapping upland runoff sediments (FAO 2007). wood, and charcoal, and non-wood products such as nipa palm Water quality and sediment management: Mangrove forests shingles, bark for tannin, traditional foods, dyes, and resins. protect freshwater supplies, or inland aquifers, from salination Sustainable harvesting is required to ensure the continuity and by serving as a ground water pump and barrier between the the quality of the mangrove forest (Bann 1998). aquifers and the sea. Mangroves also improve water quality by Tourism and recreation: Mangrove forests are attractive trapping sediments as their roots and forest complexity slow destinations for ecotourism and offer important nature-based down water flow and promote the capture and stabilization tourism opportunities (Spalding and Parrett 2019). They filter of sediment. This facilitates sediment deposition and removes out sedimentation in offshore seagrasses and coral reefs and toxins and nutrients (Bann 1998). provide environments for snorkeling and scuba diving (Bann 1998). 200 201 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: Mangroves occur in tropical and subtropical coastlines between the 30° North Slope: Mangroves develop in relatively flat intertidal areas. The more extensive the shallows are, the and South of the Equator, approximately following the 20°C (68°F) isotherms of seawater temperature greater the extent of mangrove development. On steep shores with shelves, where the shallow water zone Rainfall and freshwater supply influence the distribution of mangroves through the reduction of salinity is narrower, only fringe communities develop (Hutchings and Saenger 1987). in an otherwise highly saline environment. In areas with low, irregular, or limited seasonal rainfall or lack of freshwater input, the number of mangrove species that can survive is limited (Spalding et al. 1997). Hybrid infrastructure: In cases where protective infrastructure does not restrict mangrove development and does not impede landward migration in response to sea level rise, mangroves can be effectively Hydrology: Development of mangroves is restricted to the intertidal zone. combined with berm or levee infrastructure because they can reduce wave action and overflow. However, planting schemes on the levees should be avoided as they could produce potential damage of the roots to levees’ slopes. Salinity: Best development of mangroves seedlings ranges from a salinity of 3–27 ppt. The resistance against salinity depends on species and life stage (Krauss et al, 2008). Seedlings are less resistant than adult trees, and the tolerance increases with the age (Kathires and Dimensions: For effective wave action attenuation and protection against tsunamis, mangrove forests Bingham 2001). require complexity, width, and density of trees (Spalding et al. 2014). A width of at least 150 meters is required for sufficient wave dampening (Othman 1994). Additionally, the type of species and the density Inundation time: Mangroves require regular tidal flooding. Typical mangrove species of the forest affects the effectiveness of mangroves (Hashim and Catherine 2013). Data analysis shows: such as Avicennia spp. and Sonneratia require between 7 and 13 hours a day (van Loon • 100 m of Sonneratia forest can reduce wave energy up to 50% (Alongi 2008). et al. 2007). • 50 m of Avicennia forest is sufficient to reduce waves from 0.3 to 1 m in Sungai Besar, Malaysia, corresponding to 70% wave height reduction (Othman 1994). Wave exposure: Low. Protected coastlines are essential for mangrove communities. High URBAN wave exposure or currents can erode the sediment and lead to mangrove loss (Balke et al, 2011). Sedimentation rate: Mangroves require sediments to sustain their elevation in the tidal Land use: Coasts, park areas in coastal and river mouth areas, and natural reserve areas are well suited range (Van Santen et al. 2007). for mangrove forests. Soil: Mangroves grow on different substrates, but the most extensive mangroves are located in mud and Urban density: Suitable urban density for mangrove forests ranges from low to medium. muddy soils, usually found along delta coasts, in lagoons, and along estuarine shorelines (Hutchings and Saenger 1987). Area: Large to extra-large. Mangrove forests are NBS typically designed for application at a city and river Water quality: Mangroves are not suitable for areas with eutrophicated water or polluted water. High basin scale as they require sufficient width and extent to represent an effective buffer against storms and nutrient content harms mangrove development and reduces the resilience of mangroves to changes deliver other services, for example, nurseries for fisheries. (Lovelock et al, 2009). Integrated urban planning: Mangrove forests can be an integral component of ecoconservation programs, TECHNICAL tourism programs, food provision program, and new urban parks. MAINTENANCE Natural regeneration: Mangrove forests require propagules (mangrove seedlings) for natural mangrove establishment. If these are not available, human intervention is required for sowing or planting; successful restoration also requires restoring the hydrological conditions and enough supply of sediment New seedlings may also require protection from waves and strong currents through the installation of Mangroves require monitoring strategies to control the correct establishment and evolution of the system, and intertidal temporary protection, such as permeable dams, until the mangroves reach enough complexity to retain dynamics that should keep a balance between marine seawater and freshwater input. Policies and management plans must the soil (EcoShape n.d). ensure that the restored areas are able to maintain the hydrological processes for a functional mangrove forest. 202 203 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land in The costs of mangrove restoration Maintenance of mangrove forests deltas and coastal intertidal areas can vary considerably depending on is necessary due to the complex is required for mangrove forest location, project area, site conditions, interplay of upstream (land) and protection and restoration. specific restoration activities to be downstream (ocean) processes on implemented, and local labor and mangrove health. Maintenance will Land may be public or private. material costs. involve addressing upstream and Surface of land required for downstream threats to mangrove protection and/or restoration of health, as well as replanting mangroves may range from small mangroves in project sites depending to large extents, with different on mangrove survival rates. costs associated to the type of development and land uses. Engagement and collaboration with landowners and stakeholders are necessary. Example land-related costs: • Land acquisition • Land use (e.g., payments to landowners) • Land protection costs, including managing and controlling access • Community resettlement UNIT COST EXAMPLES THROUGHOUT THE GLOBE • A review of projects found that mangrove restoration mangrove planting and replanting (US$85,000 in first- costs could range from US$225–US$216,000/ha in year costs), including seed, bamboo, rope, labor, boats developed countries, excluding the costs of the land and fuel) (Hakim 2016). (Lewis 2005). • For Vietnam, mangrove maintenance has been • Globally, a meta-analysis provided a global cost estimated at US$7.1/ha, at least four years after range from US$500–US$54,300/ha. (Narayan et al. planting seedlings (Marchand 2008). 2016), whereas other global analysis determined that • In Kenya, a restoration project of mangrove ecosystem mangrove restoration costs range from US$1,506– cost around US$1,548.6, with preparation and planting US$49,324/ha (Bayraktarov et al. 2016). costs, and US$143 for annual thinning and maintenance • In the Caribbean, restoration-site costs are US$5,077/ costs (Kairo et al. 2009). ha (Adame et al. 2015). • Maintenance costs for mangrove restoration in • In Thailand, mangrove rehabilitation costs range from Indonesia were estimated as roughly 10% of total US$8,812–US$9,318/ha (Barbier 2007). planting costs (Hakim 2016), at US$258,000 per year • Restoration costs for mangrove restoration in for a semipermeable dam, including dam construction Indonesia included semipermeable dam construction and materials, and US$8,600 per year for mangrove (US$260,000 in first-year costs that included site replanting. preparation, material, and construction), and Mangrove Forest Management Center, Indonesia Photo by Sri Ferrdian on Unsplash 204 205 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned about mangrove forests, drawn from the growing popularity of NBS throughout the globe. Project #1: Sanya Mangrove Ecological Park, 2015–19 Project #3: Mangrove Restoration at Gazi Bay, 2004–09 Location: Hainan Island, China Location: Gazi Bay, Kenya Description: The 30-year urban development has brought Description: Gazi Bay mangrove forests have been used by local tremendous ecological damage to Sanya. Detritus from garbage people as a source of building and fuel wood as well as for fishing. covered waterways and the concrete flood wall had erased Consequently, significant mangrove deforestation occurred, with the mangrove and floodplain ecosystem, and had blocked the much of the forests cut down or otherwise degraded. Without connection between sea water and rainwater in upstream cities. the trees, the shores of the bay became muddy and vulnerable to The goal of the design was to restore the mangrove ecosystem and erosion. Recent mangrove rehabilitation projects used a community to demonstrate other urban restoration and ecological restoration participatory approach to restore degraded areas of Gazi Bay and projects. The design solved four major site problems for mangrove successfully restored the functions of mangroves so they could restoration: strong tropical monsoon floods gathered in the upper continue providing goods and services to the local community, reaches; polluted urban runoff; travel ability, and combining public while maintaining the integrity of its own ecosystem. The project recreation with natural restoration. The Park is a great success in included the planting of 6,077 mangrove trees in 46 experimental restoration and not only demonstrates its benefits to nature, but plots. Following the restoration, the women of Gazi, with support Photo by Kongjian Yu / Turenscape also brings tremendous improvement to public services. Photo by Rob Barnes / GRID-Arendal from the Kenya Marine and Fisheries Research Institute, established Benefits an ecotourism venture that benefits from the value of the Flood Protection, Recreation, Biodiversity, and Education. mangrove's scenic beauty and biodiversity. Source Benefits Turenscape Landscape Architecture Flood Protection, Social, Economy, Education. Mangrove Showcase of Environmental https://www.turenscape.com/en/project/detail/4654.html Mangrove Community Gender Source restoration ecological stewardship restoration involvement empowerment Society of Ecological Restoration (SER) approach restoration in a approach https://www.ser-rrc.org/project/kenya-mangrove-restoration-at- city environment gazi-bay/ Project #2: Mangrove plantation in Vietnam, 1994–2005 Project #4: Liberia’s Mangrove Forests and Coastal Mangrove, Location: Thai Bin, Vietnam 2011–14 Description: Restoration and rehabilitation of mangrove Location: Liberia forests have been a central focus of both governmental and Description: Since the 1980s, almost 65% of Liberian mangrove nongovernmental actors in Vietnam, as a means to combat the forests have disappeared, owing to urbanization, construction of loss of natural coastal protection by safeguarding sea levees, infrastructure, mining, and oil extraction. Recent conservation and reducing the risk of flooding and protecting livelihoods. The restoration efforts called for an extensive community engagement investment has translated into the creation of 9,462 hectares process with various stakeholders working together to establish of forest (8,961 of them mangroves) in 166 communes and the new and more sustainable land use rules. As a result, marine protection of approximately 100 km of levee lines. It is estimated and coastal protection areas were established, to significantly that approximately 350,000 beneficiaries were reached directly by impact agriculture, fisheries, and forestry. In addition to ecosystem the project’s intervention, while another 2 million were indirectly restoration objectives, mangrove protection and restoration protected through the afforestation efforts. Mangroves have also measures were viewed within the framework of economic had a positive impact on the provision of additional income for development and poverty alleviation. The project anticipates Photo by Piqsels coastal communities through an increase yield of aquaculture Photo by David Stanley on Flickr increased employment, new enterprise, and property ownership as products such as shells and oysters. beneficial outcomes Benefits Benefits Flood Protection, Community, Health and Wellbeing, Economy. Flood Protection, Social, Economy, Education, Gender Source Empowerment. International Federation of Red Cross and Red Crescent Societies Source Mangrove Equitable Boost Mangrove Community Awareness of restoration distribution economic (IFRC) protection based land key government Global Environment Facility (GEF), World Bank approach of flood growth http://ifrc-media.org/interactive/wp-content/uploads/2016/06/2.- approach use mapping agencies and local https://www.conservation.org/docs/default-source/gef-documents/ protection Mangrove-plantation-in-Viet-Nam.pdf communities liberia-mangroves/5712-liberia-mangroves-stakeholder- engagement-plan.pdf?sfvrsn=8e6d8c96_2 206 207 REFERENCES Adame, M. F., Hermoso, V. K., Perhans, K., Lovelock, C. E., and Herrera-Silviera, J. A. 2015. Selecting costeffective areas Menéndez, P., Losada, I.J., Torres-Ortega, S., Narayan, S., and Beck, M.,W. 2020. Global Flood Protection Benefits of for restoration of ecosystem services. Conservation Biology, 29:493–501 Mangroves. Scientific Reports volume 10, Article: 4404. Alongi, D.M. 2002. Present state and future of the world's mangrove forests. Environmental Conservation, 331–49. Murdiyarso, D., Purbopuspito, J., Kauffman, J.B., Warren, M.W., Sasmito, S.D., Donato, D.C., Manuri, S., Krisnawati, H.,Taberima S., and Kurnianto, S. 2015. The potential of Indonesian mangrove forests for global climate change Alongi, D.M. 2008. Mangrove forests: resilience, protection from tsunamis, and responses to global climate change. mitigation. Nature Climate Change, 5:1089–092. https://www.nature.com/articles/nclimate2734 Estuarine, Coastal and Shelf Science, 76(1)1–13. Narayan, S., Beck, M.W., Reguero, B.G., Losada, I.J., Van Wesenbeeck, B., Pontee, N., Sanchirico, J.N., Ingram, J.C., Lange, Alongi, D.M. 2012. Carbon sequestration in mangrove forests. Carbon Management, 3(3)313–22. G.M., and Burks-Copes, K.A. 2016. The effectiveness, costs and coastal protection benefits of natural and nature-based defences. PLOS Climate, 11(5); e0154735. Balke, T., Bouma, T.J., Horstman, E.M., Webb, E.L., Erftemeijer, P.L. and Herman, P.M., 2011. Windows of opportunity: thresholds to mangrove seedling establishment on tidal flats. Marine Ecology Progress Series, 440, 1–9. Othman, M.A. 1994. Value of mangroves in coastal protection. Hydrobiologia, 285(1)277–82. Bann, C. 1998. Economic valuation of mangroves: a manual for researchers. EEPSEA special paper/IDRC. Regional Office Spalding, M., Blasco, F., and Field, C. 1997. World Mangrove Atlas. International Society for Mangrove Ecosystems, for Southeast and East Asia, Economy and Environment Program for Southeast Asia. Okinawa, Japan. Barbier, E.B., and Cox, M. 2003. Does economic development lead to mangrove loss? A cross‐country analysis. Spalding, M., McIvor, A,. Tonneijck, F.H., Tol, S., and van Eijk, P. 2014. Mangroves for coastal defence. Guidelines for Contemporary Economic Policy, 21(4)418–32. coastal managers and policy makers. Wetlands International and The Nature Conservancy. 42. Barbier, E.B. 2007. Valuing ecosystem services as productive inputs. Economic Policy, 22(49)178–229. Spalding, M., and Parrett, C.L. 2019. Global patterns in mangrove recreation and tourism. Marine Policy; volume 110. https://doi.org/10.1111/j.1468-0327.2007.00174.x https://doi.org/10.1016/j.marpol.2019.103540 Barbier, E.B., Hacker, S.D., Kennedy, C., Koch, E.W., Stier, A.C., and Silliman, B.R. 2011. The value of estuarine and coastal Taillardat, P., Friess, D.A., and Lupascu, M. 2018. Mangrove blue carbon strategies for climate change mitigation are most ecosystem services. Ecological Monographs, 81(2)169–93. effective at the national scale. Biology Letters; 24 October 2018. https://doi.org/10.1098/rsbl.2018.0251 Bayraktarov, E., Saunders, M.I., Abdullah, S., Mills, M., Beher,J., Possingham, H.P., Mumby, P.J., and Lovelock, C.E. 2016. Valiela, I., Bowen, J.L., and York, J.K. 2001. Mangrove Forests: One of the World's Threatened Major Tropical The cost and feasibility of marine coastal restoration. Ecological Applications, 26(4)1055–074. Environments Bioscience, 51(10)807–15. Deltares (Institute). Mangrove restoration: to plant or not to plant? Van Loon, A.F., Dijksma, R. and Van Mensvoort, M.E.F., 2007. Hydrological classification in mangrove areas: a case study https://www.deltares.nl/app/uploads/2016/07/Mangrove-restoration_to-plant-or-not-to-plant.pdf in Can Gio, Vietnam. Aquatic Botany, 87(1), 80–82. Ecoshape https://www.ecoshape.org/en/concepts/rehabilitating-mangrove-belts/biosphere-all-living-organisms/ Van Santen, P., Augustinus, P.G.E.F., Janssen-Stelder, B.M., Quartel, S. and Tri, N.H., 2007. Sedimentation in an estuarine mangrove system. Journal of Asian Earth Sciences, 29(4), 566–575 Food and Agricultural Organization of the United Nations (FAO). 2007. The world’s mangroves 1980–2005. FAO Forestry Paper 153. Food and Agricultural Organization of the United Nations, Rome, Italy. Worthington, T.A., Zu Ermgassen, P.S., Friess, D.A., Krauss, K.W., Lovelock, C.E., Thorley, J., Tingey, R., Woodroffe, C.D., Bunting, P., Cormier, N. and Lagomasino, D., 2020. A global biophysical typology of mangroves and its relevance for Hakim, L.L. 2016. Cost and Benefit Analysis for Coastal Management. A Case Study of Improving Aquaculture and ecosystem structure and deforestation. Scientific reports, 10(1), 1–11. Mangrove Restoration Management in Tambakbulusan Village Demak Indonesia. MSc Thesis; Wageningen University and Research Centre. Zu Ermgassen, P.S., Mukherjee, N., Worthington, T.A., Acosta, A., da Rocha Araujo, A.R., Beitl, C.M., Castellanos-Galindo, G.A., Cunha-Lignon, M., Dahdouh-Guebas, F., Diele, K. and Parrett, C.L., 2021. Fishers who rely on mangroves: Modelling Hashim, A.M. and Catherine, S.M.P. 2013. Effectiveness of mangrove forests in surface wave attenuation: a review. and mapping the global intensity of mangrove-associated fisheries. Estuarine, Coastal and Shelf Science, 248, 107159. Research Journal of Applied Sciences, Engineering and Technology, 5(18)4483–88. Hutchings, P. and Saenger, P. 1987. Ecology of mangroves. University of Queensland Press, 1987. Kathiresan, K. and Bingham, B.L. 2001. Biology of mangroves and mangrove ecosystems. Krauss, K.W., Lovelock, C.E., McKee, K.L., López-Hoffman, L., Ewe, S.M. and Sousa, W.P., 2008. Environmental drivers in mangrove establishment and early development: a review. Aquatic botany, 89(2), 105–127. Krauss, K.W., Doyle, T.W., Doyle, T.J., Swarzenski, C.M., from A.S., Day, R.H., and Conner, W.H. 2009. Water level observations in mangrove swamps during two hurricanes in Florida. Wetlands, 29(1)142–49. Lewis, R.R. 2001. Mangrove Restoration–Costs and Benefits of Successful Ecological Restoration. Penang, Malaysia. Lovelock, C.E., Ball, M.C., Martin, K.C. and C. Feller, I., 2009. Nutrient enrichment increases mortality of mangroves. PloS one, 4(5) e5600. Marchand, M. 2008. Mangrove restoration in Vietnam: Key considerations and a practical guide. Delft University of Technology. 208 209 FACTS AND FIGURES DESCRIPTION Salt marshes are transitional coastal wetland ecosystems with high levels of biodiversity. Tidal marshes occur along low wave energy coastlines as a result of fine sediment accumulation and colonization by halophytic or salt tolerant plants. They are a common habitat in estuaries worldwide, particularly in the middle to high latitudes, and are among the most productive ecosystems on Earth. Based on their position with respect to the mean water level, the extent of salt tolerance, and the composition of species, three main types of salt marshes exist: pioneer zone, the low marsh, and the middle or high marsh. Salt marshes serve as a buffer from storms and floods and help prevent erosion by reducing waves and surges and stabilizing sediment. They may also reduce flooding by slowing and absorbing rainwater. Salt marshes also provide other essential ecosystem services: they filter pollutants from land runoff and hence help maintain water quality; provide critical habitat for marine species at different stages; and represent carbon sinks as they accumulate carbon in the soil. Salt marsh ecology is a complex food web and biomass that comprises primary producers, and primary and secondary consumers. Among primary producers are vascular plants, macroalgae, diatoms, epiphytes, and phytoplankton, while primary consumers are composed of zooplankton, macrozoa, mollusks, and insects. The low physical energy and high grasses provide a refuge for animals and safe and abundant habitat and breeding grounds for the birds. Tides supply nutrients for plants and carry out organic material that feeds fish and other coastal organisms. Over time, salt marshes build layers of deep mud and peat, which are waterlogged, root filled, spongy, and have extremely low levels of oxygen. This capacity to grow as a physical barrier and keep pace with the rising sea level may render salt marshes instrumental in protecting human habitat from flooding. TYPE OF CITY SCALE APPROACH Neighborhood Protect Conserve existing marshes. Coastal Delta Rehabilitate, Restore, Enhance City Rehabilitate and re-establish a destroyed or degraded marsh. River basin River Mountain PROCESSES Cooling effect Carbon sequestration Water and air cleaning Biodiversity SALT MARSHES Wave and surge reduction Sediment trapping and soil elevation Folly Beach, SC, USA Photo by Bre Smith on Unsplash 210 211 VISUALIZATIONS VISUALIZATION OF SALT MARSHES IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR SALT MARSHES 2 Restore hydrology Salt marshes exist in synergy with the sea. They rely on tidal dynamics and local floods for their growth and expansion. Waves bring nutrient-rich sediment, which they capture, store, and use as 3 additional growth medium. Areas where human actions disrupted this natural connection in the past may be strategically recovered by removing obstacles, restoring the tidal influence, and sediment flows to enable the conditions for salt marsh development. 1 Mud Motor The Mud Motor technique is designed to gradually deliver additional growth to salt marshes. Dredged mud is placed out in the open, and close to the marsh, spread out so the tidal flow can slowly wash it off and deposit it in the salt marsh. This method imitates the natural sediment movement and allows the marsh to adjust gradually. The mud can be obtained from local sources, including harbor maintenance works (Baptist et al. 2021). Details of increased benefits for the urban living environment 1 2 3 Planting mats A planting mat is a bioengineered technique for salt marsh restoration. It facilitates the re-establishment of salt marsh species. Plants are grown on relatively dense coconut mats, where the roots can grow. The mats are then placed in the marsh protecting younger species during their initial growth phases. The coconut fibers degrade over time but the plants remain (EcoShape n.d.). Salt marshes facilitate the safe Land use zoning should facilitate Salt marshes provide multiple interface of the land and sea by the natural growth, expansion, and ecosystem services. They also serve adapting to tidal dynamics and migration of salt marshes while to connect the urban seafront with wave action. protecting people, property, and gray the natural system. infrastructure. 212 213 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of salt marshes. The diagram in this section shows a sampling of important benefits that salt marshes can provide to people. Water quality and sediment management Coastal flood risk reduction Coastal flood regulation Resources Biodiversity production SALT MARSHES Sea level rise adaptation Tourism and recreation Coastal erosion regulation Carbon storage and sequestration Coastal flood regulation: Salt marshes provide coastal protection from waves and storm surges. Salt marsh ecosystems reduce the Coastal flood risk reduction: Salt marshes protect coastal Carbon storage and sequestration: Like mangroves and other height of wind waves (Möller et al. 2014) and storm surges (Krauss et al. 2009; McGee et al. 2006; Wamsley 2010) through additional communities from waves and storm surges. They also reduce wetlands, salt marshes are productive ecosystems that store flow resistance by wetland vegetation and wetland geomorphology. Moreover, coastal wetlands reduce storm surges by increasing erosion by stabilizing the sediments (Davy et al. 2009). Morgan and sequester significant amounts of carbon. On average, salt the storage area along estuaries or tidal rivers (Smolders et al. 2015). et al. 2009). They are more efficient in offsetting the effect of marshes store 334 tons CO2 per ha (Alongi 2020), mostly through storms than unvegetated mudflats (Barbier et al. 2011). Key salt accumulation in the soil. As an indication of sequestration rates: Research demonstrates various effects of salt marshes on coastal flood mitigation: marsh characteristics that are positively correlated to both wave in Australian salt marshes, the annual mean sequestration rate • Salt marshes are estimated to reduce non-storm wave heights by an average of 72% (95% hCI: 62–79%) and wave energy by attenuation and shoreline stabilization are vegetation density, was estimated at 0.55 tons CO2 per ha per year (Macready et al. 60% (Narayan et al. 2016). biomass production, and marsh size (Shepard et al. 2011). 2017). • The existence of stiff rigid shrubs may be up to three times more effective in wave damping than flexible grasses (Van Veelen Resources production: Thanks to their complex structure, salt Biodiversity: Salt marshes provide important habitat with high et al. 2020). marshes provide safe and attractive habitat for young fish, diversity of plants, animals, birds, and insects. Salt marshes are • Studies in US mid-Atlantic coastal wetlands, estimate a reduction on flood water levels by 0–700 mm/km (Paquier et al. 2017). shrimp, and shellfish that are inaccessible to larger predator also crucial spaces for breeding, wintering, and feeding grounds fish (Boesch and Turner 1984). Therefore, salt marshes are also for local and migratory species of birds (McKinley et al. 2018). Other functions: Salt marshes also prevent coastal erosion (Shepard et al. 2011), protect, and stabilize coastlines by capturing and a resource to host important aquaculture and fishing; and can Many salt marsh areas, close to urban areas, are also designated storing sediments and stabilizing the soil with its roots (McKinley et al. 2018). They can also keep up with sea level rise as they can help maintain sustainable fisheries (Boesch and Turner 1984; Ramsar sites of international importance (UNESCO 1971). grow at a rate of 10 millimeters per year (Kirwan et al. 2010). Salt marsh vegetation has a significant positive effect on shoreline MacKenzie and Dionne 2008). For example, salt marshes account Water quality and sediment management: Salt marshes act stabilization as measured by accretion, lateral erosion reduction, and marsh surface elevation change (Shepard et al. 2011). for 66% of the shrimp and 25% of the blue crab production in as natural filters that purify water entering the estuary (Mitsch the Gulf of Mexico (Zimmerman et al. 2002). and Gosselink 2008). Tall grasses create friction that reduces the Tourism and recreation: Salt marshes also provide recreational velocity of river or stormwater that passes through the marsh and tourism opportunities because they are an important habitat (Morgan et al. 2009). They also capture and store suspended, for many species of birds and other wildlife. In urban areas, they nutrient-rich sediments that nourish the marsh. The ability of offer recreation, education, and research opportunities, as well salt marshes to filter water and remove pollutants benefits both as leisure pursuits (Barbier et al. 2011). adjacent ecosystems and people (Barbier et al. 2011). 214 215 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: Salt marshes occur in many coastlines in middle to high latitudes. They form the Hybrid infrastructure: Salt marshes can be effectively combined with berm or levee infrastructure in upper part of the intertidal zone—the interface between land and sea—and are strongly controlled by situations where the infrastructure does not alter the hydrological and sediment conditions that are geomorphological, physical, and biological processes shaped by local climate factors. Salt marshes rely needed for the establishment and future inland migration of salt marshes in response to sea level rise. on the tidal regime and wind–wave conditions. They develop best in bays and estuaries with low wave exposure and a surplus of fine, nutrient-rich sediment (Whitfield and Elliott 2011). Dimensions: Salt marshes require a minimum width to mitigate wave action effectively. Dependent on the marsh morphology and vegetation characteristics, a required width of at least 200 meters is required to Hydrology: Salt marshes form the upper portion of the intertidal mudflats, between the mean high-water achieve up to 40% wave mitigation (Van Loon-Steensma et al. 2015). Salt marshes of up to 6–10 km wide neap tides and the mean high water spring tides (Mccowen et al. 2017). are required to reduce storm surges (Davy et al. 2009). Salinity: Salt marshes have an average salinity between 18.0 and 35.0 ppt (Odum 1988). URBAN Current velocity: A current velocity of 1.2 m/sec is considered as an upper threshold for salt marsh edge stability (Van Loon-Steensma et al. 2012). Land use: Natural estuaries, coastal areas, parks, and nature preserves in intertidal environments are adequate areas for salt marshes. Wave exposure: Salt marshes require low to medium wave exposure. An ideal setting would balance enough sediment suspended in the marsh with transport potential through regular flooding to the upper parts of the marsh (EcoShape). Urban density: Low to medium density urban areas are suitable for salt marshes. Sedimentation rate: More than 20 mg/L concentration is necessary for marshes to keep up with conservative projections of sea level rise (Kirwan et al. 2010). Area: Large to extra-large. Salt marshes are NBS typically designed for application at a city and river basin Soil: Salt marshes grow on various substrates from pure sand to clay and peat (Olff et al. 1997). The scale as they require sufficient width and extent to represent an effective buffer against storms and deliver availability of silt and clay in the substrate increases the stability and ability to develop (Ford et al. 2016). other services. Integrated urban planning: Salt marshes can become an integral component of ecoconservation and tourism programs, representing a key attraction as part of urban parks and landscape plans. TECHNICAL Natural regeneration: Salt marsh formation normally occurs naturally, from the seeds and propagules MAINTENANCE of established marshes. Seeds and propagules are transported by water. They can travel large distances and establish in new places quickly. Where natural colonization does not occur, restoration techniques can be used to start the process by restoring its hydrology and addressing the causes of limited sediment Salt marshes require monitoring to control their establishment and evolution. Policies and management plans should prevent supply. Artificial sowing or planting, for example using planting mats or seedlings, can be used to restore encroachment on the restored areas and maintain the appropriate hydrological conditions. The required maintenance should and build a marsh (EcoShape n.d.). be included in the restoration strategy. Some techniques, such as salt marsh restoration by dredging and added nourishment, may require significant maintenance, while other restoration approaches that employ brushwood dams or similar permeable Slope: Salt marshes develop on slopes ranging from 1:50 to 1:500. A new marsh would typically require structures, have additional costs. However, these maintenance approaches can increase growth and success rates (Vuik et to be set on a slope of 1:100 (Van Duin and Dijkema 2012). Slopes and tidal ranges determine three zones al. 2019). in a salt marsh: • Pioneer zone: 40 cm below mean high tide (MHT); • Low marsh: inundated during mean spring tides (100–400 floods per year); • Middle or high marsh: with fewer than 100 floods per year. 216 217 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land in Restoration costs associated with Maintenance needs for salt marshes coastal intertidal areas is required for salt marshes includes removal will depend on how well the marshes salt marsh protection and restoration. of obstacles to hydrological flow, are functioning; but in general terms, dredging, and adding nourishing maintenance costs for functional salt Land ownership may be public or materials (Vuik et al. 2019). marshes are low. private. However, climate change, storm Land area required for salt marsh surges, and upstream process on land protection and/or restoration is large, may impact salt marsh functioning which increases costs associated and and health. To support effective makes engagement and collaboration performance, maintenance will with multiple landowners and include monitoring to identify plant stakeholders necessary. health and may include dredging and nourishment. The use of permeable Example land-related costs: structures constructed for salt marsh • Land acquisition restoration may also be required. • Land use (e.g., payments to landowners) • Land protection costs, including managing and controlling access • Community resettlement UNIT COST EXAMPLES THROUGHOUT THE GLOBE • Median restoration costs for salt marshes from a • In New York City, costs for marsh-edge restoration have global study are estimated at US$11,100/ha but can been estimated at US$1.54 million/ha (Propato et al. range from US$100—US$33,000/ha (Narayan et al. 2018). 2016). • Monitoring costs of salt marshes can be significant, • A study from New England, in the U.S., estimated on average accounting for 15% of total project costs that salt marsh restoration cost US$39,500/ across eleven salt marsh restoration projects in New ha (US$16,000/acre) on average across eleven England (Louis Berger and Associates 1997). projects, with planning construction, and monitoring accounting for about 10%, 75%, and 15% of total restoration costs, respectively (Louis Berger and Associates 1997). • Capital costs for salt marsh restoration in the UK is estimated to range from US$14,800—US$81,000/ha of restored habitat, including land acquisition costs (Cambridge Econometrics 2021). NJ, USA Photo by James Loesch on Flickr 218 219 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned about mangrove forests, drawn from the growing popularity of NBS throughout the globe. Project #1: Salt Marsh Development in Delfzijl; Marconi project, Project #3: Shorter’s Wharf Restoration, 2002 to date 2018–21 Location: Chesapeake Bay, USA Location: Delfzijl, The Netherlands Description: A group of conservation partners—U.S. Fish and Description: Delfzijl project is restoring salt marshes by reusing Wildlife Service, the Audubon Society, the Conservation Fund, sediment from the port of Delfzijl and the Eems-Dollard Estuary. The Maryland Department of Natural Resources, and the U.S. project was launched by the municipality of Delfzijl and is a part of Geological Survey—are leading a series of experiments, which focus the Marconi Buitendijks regional development effort. In addition to on the preservation and restoration of the Chesapeake Bay marsh. testing the technical aspects of salt marsh restoration, the project 26,000 cubic yards of sediment dredged from the Blackwater River addresses several major issues faced by the municipality: a shrinking were mixed with water and sprayed across 40 acres of inundated population, sea level rise combined with subsidence, and the poor marsh in the beginning of the project. This allowed between 4 and ecological condition of the Ems-Dollard. The new marsh will improve 6 inches of sediment to accumulate and raise the surrounding area water quality, provide new habitat for many species, enhance coastal to the elevation of high marsh. Subsequently, 213,000 clumps of defenses, and increase the attractiveness of the coast for tourism and grass were planted, followed by the removal of earth and additional recreation. The know-how generated by the project will be available planting of hundreds of thousands of marsh plants. Lessons learned Photo by Martin Baptist to other locations through technical manuals. Photo by U.S. Army Corps of Engineers on Flickr from this project are shared with specialists working to restore Benefits other endangered marshes and attempting to replicate this success. Flood protection, Biodiversity, Ecotourism, Education. Benefits Source Flood protection, Health, Education, Biodiversity. Ecoshape, Rijkswaterstaat, Municipalities of Delfzijl and Eemsmond. Source Salt marsh Regional Knowledge https://www.ecoshape.org/en/pilots/saltmarsh-development- Salt marsh Sediment Funded by U.S. Fish and Wildlife Service, Audubon Society, The Conservation restoration development development marconi-delfzijl-9/ restoration reuse from environmental Fund, Maryland DNR, and the U.S. Geological Survey approach effort for applicability https://www.sciencedirect.com/science/article/pii/ approach adjacent agencies https://www.audubon.org/news/the-ambitious-plan-save- S2772411521000057?via%3Dihub sources. chesapeake-bays-shrinking-saltmarshes Project #4: Pioneer Salt Marsh Restoration For Coastal Protection, Project #4: Lincoln Park Wetlands Restoration, 2009–15 2012 to date Location: New Jersey, USA Location: Eastern Scheldt, the Netherlands Description: A large tidal marsh adjacent to Lincoln Park in Jersey Description: The Eastern Scheldt witnesses continuous erosion of City, N.J. became a landfill without a permit. The wetlands, streams, the intertidal flats and the decline of salt marshes. The Pioneer and salt marshes were blighted and full of illegally dumped debris. Salt Marsh is on the brink of disappearance. The Eastern Scheldt The area was not a healthy habitat for birds and fish nor an restoration project is testing a new method of re-establishing effective coastline support against future effects of climate change. Spartina anglica or cord grass. The new marsh protects higher With help from WSP, the New Jersey Department of Environmental intertidal areas against erosion and will continue to expand. With Protection received US$10.6 million to restore 42 acres of wetlands sufficient tidal action and the sediment input, the grasses sustain at Lincoln Park. A tidal marsh was designed to fit into the natural a healthy population of species and support the biodiversity and landscape while also meeting the recreational and public space ecological functioning of the larger area. Re-established salt needs of Hudson County. In addition, the design incorporated marshes have added social value in the form of educational, beneficial reuse of dredged material coming from the Hudson River. recreational, and scenic opportunities. The natural technology used Benefits Photo by NIOZ for this project can be used in other regions worldwide. Photo by ACG Travel Videos Flood protection, Recreation, Wildlife. Benefits Source Flood protection, Biodiversity, Ecotourism, Education. NJ Department of Environmental Protection, WSP Source https://www.state.nj.us/dep/nrr/restoration/lincolnpkwest.html IMARES, NIOZ, Ecoshape. https://www.ecoshape.org/en/cases/pioneer-salt-marsh-%20 Salt marsh Boost sustainable Knowledge Salt marsh Creation of a Money saving by restoration activities for development restoration-for-coastal-protection-eastern-scheldt-nl/ restoration new urban park reusing dredged approach citizens for future approach and recreation sediments from application amenities adjacent sources 220 221 REFERENCES Alongi, D.M. 2012. Carbon sequestration in mangrove forests. Carbon Management, 3(3)313–22. Narayan, S., Beck, M.W., Reguero, B.G., Losada, I.J., Van Wesenbeeck, B., Pontee, N., Sanchirico, J.N., Ingram, J.C., Lange, Barbier, E.B., Hacker, S.D., Kennedy, C., Koch, E.W., Stier, A.C., and Silliman, B.R. 2011. The value of estuarine and coastal G.M. and Burks-Copes, K.A., 2016. The effectiveness, costs and coastal protection benefits of natural and nature-based ecosystem services. Ecological Monographs, 81(2)169–93. defences. PloS One, 11(5): e0154735. Bakker, J.P., Bunje, J., Dijkema, K., Frikke, J., Hecker, N., Kers, B., Körber, P., Kohlus, J. and Stock, M. 2005. Wadden Sea Odum, W.E. 1988. Comparative ecology of tidal freshwater and salt marshes. Annual Review of Ecology and Systematics, Quality Status Report 2004, Wadden Sea Ecosystem, No. 19. Trilateral Monitoring and Assessment Group, pp.163-179. 19(1)147–76. Baptist, M.J., Gerkema, T., Van Prooijen, B.C., Van Maren, D.S., Van Regteren, M., Schulz, K., Colosimo, I., Vroom, J., Olff, H.D., De Leeuw, J., Bakker, J.P., Platerink, R.J. and Van Wijnen, H.J., 1997. Vegetation succession and herbivory in Van Kessel, T., Grasmeijer, B. and Willemsen, P., 2019. Beneficial use of dredged sediment to enhance salt marsh a salt marsh: changes induced by sea level rise and silt deposition along an elevational gradient. Journal of Ecology, development by applying a ‘Mud Motor’. Ecological engineering, 127, pp.312-323. 799–814. Baptist, M.J., Dankers, P., Cleveringa, J., Sittoni, L., Willemsen, P.W.J.M., van Puijenbroek, M.E.B., de Vries, B.M.L., Leuven, Paquier, A.E., Haddad, J., Lawler, S., and Ferreira, C.M. 2017. Quantification of the attenuation of storm surge J.R.F.W., Coumou, L., Kramer, H. and Elschot, K., 2021. Salt marsh construction as a Nature-Based Solution in an estuarine components by a coastal wetland of the US Mid Atlantic. Estuaries and Coasts, 40(4), 930–46. Social-Ecological System. Nature-Based Solutions, 100005. Propato M, Clough JS, Polaczyk A. 2018. Evaluating the costs and benefits of marsh-management strategies while Boesch, D.F. and Turner, R.E. 1984. Dependence of fishery species on salt marshes: the role of food and refuge. accounting for uncertain sea-level rise and ecosystem response. PLoS ONE 13(8): e0200368. Estuaries, 7(4)460–68. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0200368 Davy, A.J., Bakker, J.P., and Figueroa, M.E. 2009. Human modification of European salt marshes. Human impacts on salt Shepard C.C., , Crain, C.M., and Beck, M.,W. 2011. The Protective Role of Coastal Marshes: A Systematic Review and marshes: a global perspective. University of California Press, Berkeley, California, USA. 311–336. Meta-analysis. PLos One. https://doi.org/10.1371/journal.pone.0027374 EcoShape. Smolders, S., Plancke, Y., Ides, S., Meire, P., and Temmerman, S. 2015. Role of intertidal wetlands for tidal and storm tide https://www.ecoshape.org/en/cases/pioneer-salt-marsh-restoration-for-coastal-protection-eastern-scheldt-nl/ attenuation along a confined estuary: a model study. Natural Hazards and Earth System Sciences, 15(7) 1659–75. construction-phase/ https://www.ecoshape.org/en/concepts/growing-salt-marshes/biosphere/ Stark, J., Plancke, Y., Ides, S., Meire, P., and Temmerman, S. 2016. Coastal flood protection by a combined nature-based https://www.ecoshape.org/en/concepts/growing-salt-marshes/hydrosphere-salt-marshes/ and engineering approach: Modeling the effects of marsh geometry and surrounding dikes. Estuarine, Coastal and Shelf Science, 175:34–45. Ford, H., Garbutt, A., Ladd, C., Malarkey, J., and Skov, M.W. 2016. Soil stabilization linked to plant diversity and environmental context in coastal wetlands. Journal of Vegetation Science, 27(2) 259–268. UNESCO. 1971. "The Convention on Wetlands". Kirwan, M.L., Guntenspergen, G.R., D'Alpaos, A., Morris, J.T., Mudd, S.M., and Temmerman, S. 2010. Limits on the Van Duin, W.E. and Dijkema, K.S., 2012. Preconditions for salt marsh development in the Wadden Sea and the start of a adaptability of coastal marshes to rising sea level. Geophysical Research Letters, 37(23). salt marsh opportunities map (No. C076/12). IMARES. (Dutch) Krauss, K.W., Doyle, T.W., Doyle, T.J., Swarzenski, C.M., From, A.S., Day, R.H., and Conner, W.H. 2009. Water level Van Loon-Steensma, J.M., 2015. Salt marshes to adapt the flood defences along the Dutch Wadden Sea coast. Mitigation observations in mangrove swamps during two hurricanes in Florida. Wetlands, 29(1)142–49. and adaptation strategies for global change, 20(6)929–48. Louis Berger and Associates. 1997. Costs for wetland creation and restoration projects in the glaciated Northeast. U.S. Van Loon-Steensma, J.M., De Groot, A.V., Van Duin, W.E., Van Wesenbeeck, B.K., Smale, A.J., Meeuwsen, H.A.M. and Environmental Protection Agency, Region 1, Boston, Massachusetts. Wegman, R.M.A. 2012. Search map for salt marshes and water safety in the Wadden area: an exploration of locations in the Wadden area where existing salt marshes or salt marsh development could potentially contribute to water safety MacKenzie, R.A. and Dionne, M. 2008. Habitat heterogeneity: importance of salt marsh pools and high marsh surfaces to (No. 2391). Alterra. (Dutch) fish production in two Gulf of Maine salt marshes. Marine Ecology Progress Series, 368: 217–30. Van Veelen, T.J., Fairchild, T.P., Reeve, D.E. and Karunarathna, H., 2020. Experimental study on vegetation flexibility as McGee, B.D., Goree, B.B., Tollett, R.W., Woodward, B.K., and Kress, W.H. 2006. Hurricane Rita surge data, southwestern control parameter for wave damping and velocity structure. Coastal Engineering, 157:103648. Louisiana and southeastern Texas, September to November 2005.. Data Series 220. USGS Publications Warehouse. Whitfield, A. and Elliott, M. 2011. Ecosystem and biotic classifications of estuaries and coasts. In book: Treatise on McKinley, E., Ballinger, R.C., and Beaumont, N.J. 2018. Saltmarshes, ecosystem services, and an evolving policy Estuarine and Coastal Science, 99–124. landscape: A case study of Wales, UK. Marine Policy, 91:1–10. Vuik, V., Borsje, B.W., Willemsen, P.W. and Jonkman, S.N., 2019. Salt marshes for flood risk reduction: Quantifying long- Mcowen, C.J., Weatherdon, L.V., Van Bochove, J.W., Sullivan, E., Blyth, S., Zockler, C., Stanwell-Smith, D., Kingston, N., term effectiveness and life-cycle costs. Ocean & Coastal Management, 17196–110. Martin, C.S., Spalding, M., and Fletcher, S. 2017. A global map of saltmarshes. Biodiversity Data Journal, (5). Wamsley, T.V., Cialone, M.A., Smith, J.M., Atkinson, J.H., and Rosati, J.D. 2010. The potential of wetlands in reducing Mitsch, W. J. and J. G. Gosselink. 2008. Wetlands. Van Nostrand Reinhold, New York, New York, USA. storm surge. Ocean Engineering, 37(1)59–68. Möller, I., Kudella, M., Rupprecht, F., Spencer, T., Paul, M., Van Wesenbeeck, B.K., Wolters, G., Jensen, K., Bouma, T.J., Miranda-Lange, M., and Schimmels, S. 2014. Wave attenuation over coastal salt marshes under storm surge conditions. Nature Geoscience, 7(10)727–31. Morgan, P.A., Burdick, D.M. and Short, F.T., 2009. The functions and values of fringing salt marshes in northern New England, USA. Estuaries and Coasts, 32(3)483–95. 222 223 FACTS AND FIGURES DESCRIPTION Sandy shores represent the interphase between ocean and land and form a first line of defense for many coastal cities globally from wave action, storm surges, and wind impact. Sandy shorelines often include beach systems of different typologies, dunes and other features such as submerged biogenic reefs or seagrass meadows. Beaches are accumulations of unconsolidated and non-cohesive sediment and are largely controlled by the slope of the inner shelf and coastal area, abundance and type of sediments, tidal range, and wave energy (Wright and Short 1984). Dunes are accumulations of sand transported by wind to the backshore and stabilized by vegetation or other structures. Dunes protect against flood and erosion during storm conditions and represent sand reservoirs that naturally nourish the shoreline after storms. Vegetation in dunes accumulates sediment, allows dunes to grow and is a critical element for reducing erosion, overtopping, and flooding. Coral and shellfish reefs also protect coastlines by breaking wave energy offshore. Such reefs critically influence currents and transport of sediment that shape and configure the shoreline. Seagrasses also contribute to retain sediment in the submerged part of sedimentary shorelines and play a crucial role in contributing to erosion control and carbon retention in the soil. These natural elements function in an interconnected manner and create rich ecosystems that provide many services in addition to coastal protection such as fisheries resources, carbon sequestration, cultural values, recreation, and tourism. Sandy shores are also economically valuable to cities because they accommodate coastal development and infrastructure such as boardwalks, marinas, beach accesses, and businesses associated to resources in coastal areas. However, urban development often directly conflicts with the preservation of these environments in many regions. The adverse effects of degradation, structures, and construction on the natural processes influence the coastal protection they provide. Furthermore, sand mining has led to severe erosion and flooding impacts in many regions because sand is a scarce but valuable resource in construction and industrial applications. TYPE OF CITY SCALE APPROACH Protect Neighborhood Protect the integrity of reefs, beaches, and dunes. Coastal Delta Rehabilitate, Restore, Enhance City Beach nourishment and replenishment. Create conditions for natural dune regeneration or revegetation of dunes. River basin Reef restoration and management. River Mountain PROCESSES Cooling effect Biodiversity Wave reduction Sand Infiltration trapping SANDY SHORES Water storage Fresh water balance Kerala, India Aquifer recharge Photo by Antoine Similon on Unsplash 224 225 VISUALIZATIONS VISUALIZATION OF SANDY SHORES IN THE URBAN CONTEXT SPECIAL TECHNIQUES FOR SANDY SHORES 1 Beach nourishment and dune restoration One common approach used in sandy shores for temporarily forestalling shoreline retreat or beach erosion is to artificially widen a beach with sand from some outside source, usually from an offshore continental shelf. Beach nourishment relies on feeding sand along or in front of a beach and allowing wave and tidal action to distribute it along the shore. Approaches to restore and manage 3 beach systems include shoreface or beach nourishment (nearshore placement) and dune restoration and nourishment (USACE 2021; SNH 2000). Beach nourishment requires adequate planning because adding sand without addressing causes of erosion will lead to limited success and costly periodic nourishment cycles (Griggs and Reguero 2021). 2 Artificial reefs and submerged structures Artificial reefs can work to maintain beach stability and prevent erosion by breaking waves and influencing currents that transport sediment. Artificial reefs also offer hard substrate for coral or oysters and create conditions to establish other ecosystems such as seagrass meadows, mangroves, and beach and dunes. Submerged structures can also serve to create perched beaches, where the beach profile is raised or protected. Long, low embankments parallel to the shore can provide support structures for new topography and create Details of increased benefits for the additional opportunities for biodiversity (Jacobsen 1982). urban living environment 1 2 3 Connectivity and multiple lines of defense Mangroves, seagrass meadows, reefs, and beaches and dunes are interconnected and support each other. Their flood protection also depends on maintaining healthy ecosystems. Reefs serve as submerged structures that allow lower energy environments for other ecosystems can establish and accumulate sediment in mangroves, for example. The presence of submerged and emerged vegetation can stabilize the seabed and enhance sediment deposition (Ondiviela et al. 2014; USACE 2021). A multiple line of In addition to coastal protection, Sandy shorelines provide important Dune environments represent defense with seagrasses, reefs, and beach and dune nourishment, beach and dunes offer recreational nature-based recreation opportunities. a flood control boundary that approached with an integral view, can be used to provide effective uses and represent a connection Sidewalks, structures, and other urbanization plans should take as an protection and multiple benefits. Maintaining healthy ecosystems of the city with the sea front. Reefs development on dunes and beach, important reference to protect both as a natural protection is often a no-regret, low-cost strategy, in and seagrass meadows also provide unless carefully planned, impact the the natural systems and the urban the face of increasing threats of climate change along urbanized benefits for artisanal fishing and natural processes and the protection infrastructure. coastlines. tourism. they offer during storms. 226 227 FUNCTIONS BENEFITS The diagram in this section shows relevant functions of sandy shores. The diagram in this section shows a sampling of important benefits that sandy shores can provide. Erosion and sediment management Coastal flood Social interaction Coastal flood risk reduction regulation Cultural Salt intrusion Biodiversity regulation SANDY SHORES Coastal erosion Tourism and regulation Sea level rise recreation adaptation Coastal flood regulation: Coastal beaches and dunes can prevent flooding because they dissipate wave energy (USACE 2021; Silva Coastal flood risk reduction: Sandy coastlines and dunes Social interaction: Coastal environments positively influence et al. 2016; Hanley et al. 2014). Their ability to attenuate waves depends on their geomorphology and factors including the slope, protect coastal areas from storm and flood damage. They can social aspects of human wellbeing (Cox et al. 2004). Scenic height, width, the presence of vegetation, and the volume of sand (Carter 1991; Short 1999; Hesp 1989; Hacker et al. 2012). also mitigate the effects of climate change by trapping sediment coastal zones create a strong sense of place, forging a meaningful Reefs also dissipate wave energy, and their effectiveness depends on their structural complexity, roughness, and depth. Vegetation and growing to keep pace with sea level rise and other changes relationship between people and their surroundings (Jorgensen reduces flooding through frictional effects depending on their relative submergence—height and water depth—density and size in environmental conditions (Cunniff and Schwartz 2015; Silva and Stedman 2001). A strong bond between the community and (USACE 2021). et al. 2016). its environment helps build social cohesion and deliver multiple Erosion and sediment management: Dunes buffer storm public health benefits (Shamai 1991). Other functions: Beaches, dunes, and reefs prevent coastal erosion by retaining and stabilizing sand. They can also grow with rising erosion and help the shoreline recover by naturally nourishing Culture: Beaches and dunes are a proven source of aesthetic sea levels and contributing to restore the coastline after the impact of storms (Hanley et al. 2014; Silva et al. 2016). Wider beach the shoreline during extreme events, serving as reserves of appreciation and inspiration for scientific research, cultural fronts and dunes can also protect inland resources from saltwater intrusion (Nehren et al. 2016). Reefs induce wave breaking and sand. Vegetation in dunes help prevent erosion and recover production, and art. Sites of international and national influence currents that transport sediment. Coral reefs are also sources of sediment to reef-lined coasts. from the impact of storms (Silva et al. 2016). At the same time, importance, they serve as settings for cultural, social, and vegetation is important to trap and store sand that allows dunes educational events (Nehren et al. 2016), and are an important to grow and create additional storm protection (Cunniff and part of the local cultural and environmental heritage (Pérez- Schwartz 2015). Maqueo et al. 2013). Biodiversity: Beach and dune systems provide habitats for marine, amphibian and terrestrial animals, dune vegetation, and indigenous plant species (Nehren et al. 2016). Tourism and recreation: Sandy shores offer large economic value in coastal regions because they provide tourism and recreation opportunities such as surfing, scuba diving, boating, fishing, swimming, walking, and sunbathing (Barbier et al. 2011). Beach uses and activities, when sustainably managed, can provide many opportunities that contribute to benefit local communities and the environment. 228 229 SUITABILITY CONSIDERATIONS ENVIRONMENTAL Location and climate: Sandy coastlines occur worldwide but they present very different characteristics Site evaluation and preparation: Understanding the past, present, and possible future dynamics— depending on climatic, environmental and geomorphological conditions (Luijendijk et al. 2018). Often, more specifically, sediment budgets, hydrodynamics, sediment transport, and interactions with other sandy coastlines have been highly developed and densely populated because of their real estate, tourism ecosystems—is critical for determining the scale and feasibility of a project in sandy shorelines. Where and recreational use. However, beaches are one of the most dynamic coastal geomorphic landforms, natural beaches and dunes are present, restoring, maintaining, or enhancing processes, features, and their spatial limits are not always fixed. The development and width of beaches are largely controlled dynamics should be the first goal of managers seeking to reduce flood and erosion risk (USACE 2021). by the slope of the inner shelf and coastal area, abundance and composition of sediments, tidal range, Information on coastal processes and dynamics can help to understand the causes of flooding and erosion. and wave energy (Wright and Short 1984). Dunes are part of the beach system, usually in the form of Remote sensing can also provide valuable information on coastal changes that inform effective solutions. small hills or ridges. Coral reefs mostly occur in tropical coastlines associated to warm, low nutrients and clear waters that are optimal for coral growth. Shellfish reefs are formed by bivalve mollusks, mostly A beach can also be enhanced with other elements to reduce flooding. Different techniques restore oysters and mussels, and can be found in sheltered temperate and tropical areas in bays, estuaries, and dunes that may include adding sand, revegetation, and sand trapping. However, if an existing system does nearshore environments. not have dunes historically, it often indicates that the climatic and geomorphological conditions are not suitable. Similarly, restoration of reefs and construction of artificial reefs can be planned where reefs have been degraded or historically present. Soil and geomorphology: Sandy beaches depend on the continuous transport of natural sediment by Sandy shores need designed solutions that align with the original beach and dune as much as possible. the wind, sea, and rivers. Dunes rely on the vegetation to capture and stabilize the sand (EcoSpace n.d.). Mimicking natural conditions and letting nature do most of the work—for example, by placing sediments Beach nourishment strategies require low-lying oceanfront areas with nearby sources of sand that should where winds, waves, and tides can transport them for beach and dune growth—can reduce maintenance be carefully assessed for grain size and volume of nourishment. The environmental effects of borrowing requirements substantially. The design of beaches should also consider changes in beach slope, volume, sources and placement also require careful study for long-term consequences. As with beach and dunes, and width as primary design parameters, rather than attempting to create a static system. reef-based solutions should attend to the drivers of historic degradation of natural reefs, and consider Beach replenishment may fail when it lacks: (i) a realistic assessment of potential borrow areas of sand and where natural biogenic reefs occur. volume; (ii) compatibility of added sand to the beach being nourished; (iii) construction costs and plans; (iv) attention to vulnerable geomorphic elements of the coastal zone; and (v) environmental impacts (Griggs and Reguero, 2021). TECHNICAL URBAN Urban density: Low to medium density urban areas are suitable for sandy shores. Urbanization should Dimensions: The spatial extent of the beach varies from depths where waves can mobilize sediment to occur behind stable and vegetated shorelines and should ensure setback zones. When buildings are the uppermost limit of wave action to the foreshore of the coastal profile. The foreshore usually has a developed on dunes or active parts of the beach system, flooding and erosion problems are the most steeper slope and is an active part of the beach system. Dune size and shape depend on wave action, tidal frequent consequences. range, type of sediments and vegetation and geomorphology (Davidson-Arnott 2010). Area: Large to extra-large. Local, small-scale interventions are often not effective because sediment transport processes often involve larger spatial scales and design assessments. Hybrid infrastructure: Projects in sandy shores often include structures such as breakwaters and groins to stabilize coastlines by blocking and influencing sediment transport. These solutions can be designed Integrated urban planning: Sandy shores and dune restoration can be aligned with conservation programs, for effective coastal protection but require careful design and planning for local conditions. However, but their long-term evolution requires careful consideration of the main drivers of historic degradation. coastal structures can also have detrimental effects and erosion and flooding (Mangor 2020). These With sea-level rise and increased wave action, beach nourishment will also need to be combined with effects have been amply demonstrated in many urban coastlines as in India (Muthusankar et al. 2016). other options, including adequate setback zones that can naturally nourish the system. Beach accesses or In these cases, de-engineering some of these barriers and favoring natural processes—sometimes with parking on dune system should also be restricted to specific areas to ensure the stability and integrity of nourishment cycles and dune restoration—can effectively address flooding and chronic erosion problems, dunes and vegetation and avoid degradation. as demonstrated by experiences in Colombia (Rangel-Buitrago et al. 2020). MAINTENANCE Slope and cross shore elements: Typical elements in a sandy beach and dune system may include long- shore bars or a reef system, beach cusps, and dunes. The geomorphology of beaches is very variable, but they can be broadly classified into dissipative and reflective beaches, each with different characteristics. Sandy shores are dynamic systems that pose serious management challenges, and may require regular nourishment cycles, Dissipative beaches occur in high energy environments, present surf zones 300–500 meters wide, shore and careful management (Cunniff and Schwartz 2015). Beach nourishment and dune restoration can have important normal bars and troughs, low-slopes, wide beach faces, and fine sand. Reflective beaches are characterized environmental returns, but poor designs can also lead to adverse impacts and high long-term maintenance costs. Planning by steeper narrow beach face and slopes, coarser sediment of even pebbles, a narrow surf zone, and these projects requires considering the adequate spatial and temporal scales affecting coastal change locally. Reef-based often present cusps on the upper part. Dunes have a better chance of developing over an extensive area solutions may combine structural and ecological features and maintenance may be required to maintain the environmental with gentle slopes and where wind processes can accumulate sediment (Barman et al. 2015). benefits such as coral restoration. 230 231 COSTS COST CONSIDERATIONS Construction and Land implementation Maintenance Access to or ownership of land in Protecting fragile beaches and dunes Maintenance costs of beach coastal areas may be required. can maintain their ability to protect nourishment and dune restoration coastal areas from flooding and are driven by activities such as Land ownership may be public or erosion. Protection may be sufficient recurring dredging and sand private. in areas with low erosion rates and deposition on these coastal areas sufficient beach or dune presence. and replanting of dune vegetation. Land area required will be large, The frequency and amount of sand which increases costs and makes In areas of high erosion, or where required will depend on coastal engagement and collaboration with construction or augmentation of erosion rates at the project site. multiple landowners and stakeholders beaches and dunes are necessary, necessary. beach nourishment or dune restoration can be implemented. Example land-related costs: Beach nourishment involves dredging • Land acquisition sand from offshore and harbor areas • Land use (e.g., payments to and depositing the sand on beaches landowners) and dunes. Dune restoration includes • Land protection costs, including replanting vegetation and installing managing and controlling access sand fences. Costs associated with • Community resettlement beach nourishment and dune restoration will depend on local labor, machinery, transportation, and material (e.g., sand) costs. UNIT COST EXAMPLES THROUGHOUT THE GLOBE Global estimates show that beach nourishment costs may US$456–US$188,817 m/year with a median project vary from US$4-US$21/m3 as follows: cost of US$19,791 m/year. The construction costs • US$5–US$18/m3 in the USA (Aerts et al. 2018). of structural coral reef restoration projects ranged • US$4–US$8/m3 in the Netherlands (Jonkman et al. between US$20–US$155,000 m/year with a median 2013). project cost of US$1,290 m/year. • US$5–US$11/m3 in the EU (Linhman et al. 2010). • Bayraktarov et al. (2016) determined that the average • US$7.7/m3 in Australia (Linhman et al. 2010). cost of coral reef restoration in developing countries is • US$20.8/m3 in South Africa (Linhman et al. 2010). US$377,000/ha (median value is US$89,000). • US$5–US$8/m3 in Vietnam (Böös and Dahlström • Oyster reef restoration cost on average is US$387,000/ 2015). ha. Example dune restoration costs: • The average cost of seagrass restoration is • Dune revegetation projects in Australia and the US cost US$106,000/ha in the range of US$7,636–US$13,888/ha, including Example beach and dune maintenance costs: labor, vegetation, and sand (Aerts 2018). • Maintenance costs of sand dunes from cases in Europe • In Europe, planting vegetation on dunes is estimated to are estimated atUS$336/ha/year (Verburg et al. 2017). cost US$14,484/ha (Verburg et al. 2017). • In Denmark, total maintenance costs associated with an Example of artificial reef restoration costs: artificially created dune were estimated at US$2,229/ha • Ferrario et al. (2014) identified that the costs of (Vestergaard 2012). building tropical breakwaters ranged between Guérande, France Photo by Olivier Mesnage on Unsplash 232 233 NBS IN PRACTICE The four projects in this section highlight good practices and lessons learned about sandy shores, drawn from the growing popularity of NBS throughout the globe. Project #1: Andhra Pradesh Disaster Recovery Project, 2015–21 Project #3: Dune restoration in Mauritania, West Africa Coastal Location: Andhra Pradesh, India Areas Management Program, 2018–22 Description: Andhra Pradesh is one of the most natural hazard- Location: Nouakchott, Mauritania prone states in India. 440 kilometers of its 974-kilometer coast Description: Nouakchott, the capital of Mauritania and its biggest are vulnerable to coastal erosion from tropical storms and related city, is located at or below the sea level. Its coast is protected by a hazards. The development objectives of APDRP were to restore, series of dunes exposed to erosion, sand mining, livestock grazing, improve, and enhance resilience of public services, environmental and detrimental leisure activities such as dune racing. facilities, and livelihoods in targeted communities, and to enhance The Mauritania Work project developed as part of the West Africa the capacity of state entities to respond promptly and effectively Coastal Areas Management Program prioritized the protection to crises and emergencies. Resilient electric network, restoration of Nouakchott and the reinforcement of the coastal dunes. This of connectivity and shelter infrastructure, protection of beach was accomplished by sand replenishment and the use of plants to front were a few components of the project. The project restored stabilize soil. Restrictions on dune access and use prevented further mangroves for improving coastal resilience, acting as a shelter belt. physical destruction. A subsequent phase of the project will plant Its beachfront restoration used some eco-friendly approaches. mangroves along the border with Senegal. These will act as a buffer Photo by INI Design Studio Photo by by Nicolas Desramaut / World Bank zone and further help in erosion control along the Senegal River Benefits shoreline. Additional risk reduction measures focused on the local Community, Health and Wellbeing. community are currently under preparation as part of the long-term Source resilience and adaptation plans. World Bank Benefits Integrated in a Long-term Restoration of key https://projects.worldbank.org/en/projects-operations/project- Coastal dunes Large Development Health, Social Development. comprehensive resilient environmental detail/P154847 restoration partnership of a multisector Source task of city strategy services a priority approach of coastal investment plan World Bank recovery communities https://www.wacaprogram.org/country/mauritania Project #4: Integrated Coastal Zone Management (ICZM), 2012–21 Project #4: The Sand Motor, 2009-2011 Location: Moulouya, Morocco Location: The Netherlands Description: More than half of Morocco's urban population lives Description: The Sand Motor is a mega-nourishment project along the coast. The coast is negatively affected by various forms implemented in the Delfland Coast—North Sea coast of South of pollution and unsustainable practices including the discharge of Holland, The Netherlands. This innovative pilot project tested the industrial effluents, municipal sewage, and solid waste disposal. upscaling of regular sand nourishment along the Dutch coast. Carried The Moulouya Coastal Management project cleaned and restored out by Rijkswaterstaat—part of the Dutch Ministry of Infrastructure degraded wetlands and dune ecosystems. In addition to the clear and Water Management—the Sand Motor or sand engine was a environmental improvements, the project has had a positive peninsula covering 128 ha in 2011. The program aims at preservation social impact. Direct employment of the local residents raised the of the coastline and protection against flooding. The Sand Motor average household income in the area by between 10 percent and also has the purpose to create temporary space for leisure activities 25 percent in the short term, and created a potential for further and nature development. Without the Sand Motor, the coastline income growth between 20 percent and 500 percent in the medium would require regular maintenance through frequent nourishment to long term (EU 2008). operations. By making use of natural processes to redistribute the Photo by Imad Cherkaoui Photo by Rijkswaterstaat / Jurriaan Brobbel sand over time, the Sand Motor is a buffer against sea level rise, and Benefits mitigates the impacts of storm surges and coastal flooding. Biodiversity, Ecotourism, Education, Economy. Benefits Source Education, Ecotourism, Economy. World Bank Source https://documents1.worldbank.org/curated/ Deltares Integrated Co-management: Boost economic Long term Monitoring Accessibility and coastal zone delegating growth and en/821161538145781490/pdf/Morocco-MA-GEF-Integrated- maintenance program safety for leisure https://climate-adapt.eea.europa.eu/metadata/case-studies/ management into responsibilities to alternative Coastal-Zone-Mgt.pdf plan for coastal for knowledge visitors sand-motor-2013-building-with-nature-solution-to-improve-coastal- planning local stakeholders livelihoods protection development protection-along-delfland-coast-the-netherlands/delfland-coast_ document-1.pdf 234 235 REFERENCES Aerts, J.C. 2018. A review of cost estimates for flood adaptation. Water, 10(11)1646. Luijendijk, A., Hagenaars, G., Ranasinghe, R., Baart, F., Donchyts, G., and Aarninkhof, S. 2018. The state of the world’s beaches. Scientific Reports, 8(1)1–11. Aerts, J.C., Barnard, P.L., Botzen, W., Grifman, P., Hart, J.F., De Moel, H., Mann, A.N., de Ruig, L.T., and Sadrpour, N. 2018. Pathways to resilience: adapting to sea level rise in Los Angeles. Annals of the New York Academy of Sciences, 1427(1)1– Mangor, K. 2020. Human causes of coastal erosion. http://www.coastalwiki.org/wiki/Human_causes_of_coastal_erosion 90. Muthusankar, G., Jonathan, M.P., Lakshumanan, C., Priyadarsi, D.R., and Srinivasa-Raju, K. 2017. Coastal erosion vs man- Barbier, E.B., Hacker, S.D., Kennedy, C., Koch, E.W., Stier, A.C. and Silliman, B.R., 2011. The value of estuarine and coastal made protective structures: evaluating a two-decade history from southeastern India. Nat Hazards 85, 637–47 . ecosystemservices. Ecological Monographs, 81(2)169–93. https://doi.org/10.1007/s11069-016-2583-7 Böös, S. and Dahlström, A. 2015. Coastal Evolution at Nhatrang Bay, Vietnam. Journal of Water Management and Nehren, U., Thai, H.H.D., Marfai, M.A., Raedig, C., Alfonso, S., Sartohadi, J., and Castro, C. 2016. Ecosystem services Research, 71: 223–30. of coastal dune systems for hazard mitigation: Case studies from Vietnam, Indonesia, and Chile. In: Ecosystem-based disaster risk reduction and adaptation in practice.401–433. Springer, Cham. Bayraktarov, E., Saunders,M.I., Abdullah, S., Mills, M., Beher, J., Possingham, H.P., Mumby, P.J., and Lovelock, C.E. 2016. The cost and feasibility of marine coastal restoration. Ecological Applications, 26(4)1055–1074. Ondiviela, B., Losada, I.N., Lara, J.I., Maza, M., Galván, C., Bouma, T.J., and van Belzen, J. 2014. The role of seagrasses in coastal protection in a changing climate. Coastal Engineering, 87:158–68. Carter, R. 1991. Near-future sea level impacts on coastal dune landscapes. Landscape Ecology, 6(1)29–39. Pérez-Maqueo, O., Martínez, M.L., Lithgow, D., Mendoza- González, G., Feagin, R.A., and Gallego-Fernández, J.B. 2013. Carter, R.W.G. 2013. Coastal Environments: An Introduction to The Physical, Ecological, and Cultural Systems of The coasts and their costs. In: Restoration of Coastal Dunes. 289–304. Springer, Berlin, Heidelberg. Coastlines. Elsevier. Rangel-Buitrago, N., Williams, N.,A.T., and Anfuso, G. 2018. Climate Adapt. 2015. Beach and Shoreface Nourishment. Hard protection structures as a principal coastal erosion management strategy along the Caribbean coast of Colombia. A https://climate-adapt.eea.europa.eu/metadata/adaptation-options/beach-and-shoreface-nourishment chronicle of pitfalls. Ocean & Coastal Management, 156:58–75, https://doi.org/10.1016/j.ocecoaman.2017.04.006 Cox, M.E., Johnstone, R., and Robinson, J. 2004. Effects of coastal recreation on social aspects of human well-being. Proceedings of the Coastal Zone Asia Pacific Conference. Scottish Natural Heritage (SNH). 2000. A guide to managing coastal erosion in beach/dune systems. https://www. nature.scot/sites/default/files/2017-07/Publication%202000%20-%20Beach%20Dunes%20-%20a%20guide%20to%20 Cunniff, S. and Schwartz, A. 2015. Performance Of Natural Infrastructure And Nature-Based Measures As Coastal Risk managing%20coastal%20erosion%20in%20beach%20dune%20systems.pdf Reduction Features. Environmental Defense Fund (EDF). https://www.edf.org/sites/default/files/summary_ni_literature_compilation_0.pdf Short, A.D., 1999. Handbook of Beach and Shoreface Morphodynamics (No. 551.468 HAN). Wiley. EcoShape. https://www.ecoshape.org/en/concepts/enhancing-dune-dynamics/ Short, A.D., 2012. Coastal processes and beaches. Nature Education Knowledge, 3(10)15. European Union. 2008. SMAP III. MED Region. Speybroeck, J., Bonte, D., Courtens, W., Gheskiere, T., Grootaert, P., Maelfait, J.P., Mathys, M., Provoost, S., Sabbe, K., https://europa.eu/capacity4dev/file/10357/download?token=p3vJS12O Stienen, E.W., and Lancker, V.V. 2006. Beach nourishment: an ecologically sound coastal defence alternative? A review. Aquatic conservation: Marine and Freshwater ecosystems, 16(4)419–35. Griggs, G, Reguero, B.G. 2021 Coastal Adaptation to Climate Change and Sea-Level Rise. Water, 13 (16)2151. Shamai, S. 1991. Sense of Place - an Empirical Measurement. Geoforum 22(3):347–58. Hacker, S.D., Zarnetske, P., Seabloom, E., Ruggiero, P., Mull, J.,Gerrity, S., and Jones, C. 2012. Subtle differences in two non‐native congeneric beach grasses significantly affect their colonization, spread, and impact. Oikos, 121(1)138–48. Silva, R., Martinez, M.L., Odériz, I., Mendoza, E., and Feagin, R.A. 2016. Response of vegetated dune–beach systems to storm conditions. Coastal Engineering, 109:53–62. Hanley, M.E., Hoggart, S.P.G., Simmonds, D.J., Bichot, A., Colangelo, M.A., Bozzeda, F., Huertefeux, H., Ondiviela, B., Owtrowski, R., Recio, M., Trude, R., Zawadzka-Kahlau, E., and Thompson, R.C. 2014. Shifting sands? Coastal protection by Stowa. Sand Nourishments. Foundation for Applied Water Management Research. Netherlands. sand banks, beaches and dunes. Coastal Engineering, 87:136–46. https://www.stowa.nl/deltafacts/waterveiligheid/het-kustsysteem/sand-nourishments Hesp, P.A. 1989. A review of biological and geomorphological processes involved in the initiation and development of Tan, Y.M., Dalby, O., Kendrick, G.A., Statton, J., Sinclair, E.A., Fraser, M.W., Macreadie, P.I., Gillies, C.L., Coleman, R.A., incipient foredunes. Proceedings of the Royal Society of Edinburgh, Section B: Biological Sciences, 96:181–201. Waycott, M., and Van Dijk, K.J. 2020. Seagrass restoration is possible: Insights and lessons from Australia and New Zealand. Frontiers in Marine Science, 7: 617. Houston, J.R., 2008. The economic value of beaches: a 2008 update. Shore and Beach, 76(3)22–26 USACE 2021 International Guidelines on Natural and Nature-Based Features for Flood Risk Management Jacobsen E.E. 1982. Perched beach. In: Beaches and Coastal Geology. Encyclopedia of Earth Sciences Series. Springer, https://ewn.erdc.dren.mil/?page_id=4351 New York, NY. https://doi.org/10.1007/0-387-30843-1_320 Verburg, R.W., Hennen, W.H.G.J., Puister, L.F., Michels, R., and van Duijvendijk, K. 2017. Estimating costs of nature Jonkman, S.N., Hillen, M.M., Nicholls, R.J., Kanning, W., and van Ledden, M. 2013. Costs of adapting coastal defences to management in the European Union: Exploration modelling for PBL’s Nature Outlook (No. 97). Wageningen University & sea-level rise—new estimates and their implications. Journal of Coastal Research, 29(5)1212–26. Research, Statutory Research Tasks Unit for Nature and the Environment. Jorgensen, B.S. and Stedman, R.C. 2001. Sense of place as an attitude: Lakeshore owners' attitudes toward their Vestergaard P. 2012. Natural plant diversity development on a man-made dune system. In: Martínez ML, Gallego- properties. Journal of Environmental Psychology, 21(3)233–48. Fernández JB, Hesp PA (eds) Restoration of coastal dunes, Chap. 4. Springer, Berlin Kanti Barman, N., Kumar Paul, A., Chatterjee, S., Bera, G., and Kamila, A. 2015. Coastal Sand Dune Systems: Location, Wootton, L., Miller, J., Miller, C., Peek, M., Williams, A., and Rowe, P. 2016. NJ Sea Grant Consortium Dune Manual. Sandy Formation, Morphological Characteristics Analysis through Vegetation Processes Estimation. Journal of Geography, Hook, NJ: New Jersey Sea Grant Consortium. Environment and Earth Science International, 4(4)1–8. https://doi.org/10.9734/JGEESI/2016/22383 Wright, D.L., and Short, A. 1984. Morphodynamic variability of beaches and surf zones, a synthesis. Marine Geology, Linham, M.M., Green, C.H., and Nicholls, R.J. 2010. Costs of adaptation to the effects of climate change in the world’s 56:92–118 large port cities. AVOID DECC: GAO215/GASRF, 123:2009–2012. 236 237 A natural riverbank in Rome, Italy Photo by Mark Harpu on Unsplash 238 239 240