STRATEGIES FOR URBAN STORMWATER WETLANDS STRATEGIES FOR URBAN STORMWATER WETLANDS Alan M. Berger, Heidi

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  • STRATEGIES FOR URBAN STORMWATER WETLANDS

    Alan M. Berger, Heidi Nepf, Celina Balderas Guzmán

    Project Contributors

    Tyler Swingle, Department of

    Architecture

    Waishan Qiu, Department of

    Urban Studies & Planning

    Samantha Cohen, Department

    of Urban Studies & Planning

    Manoel Xavier, Visiting Student,

    Department of Civil and Environ-

    mental Engineering

    Keywords

    Stormwater

    Green Infrastructure

    Resiliency

    Regional Planning

    Ecology

    Abstract

    Heavier rainfall due to climate change, combined with widespread wetland destruction, has led to major environmental problems in cities: urban flooding, water scarcity, and water quality problems. Wetlands, the primary landscape that could help cities cope with these problems, have been largely (if not entirely) destroyed in urban areas by the very process of city making. This project reclaims urban wetland infrastructure through strategic design, planning, and engineering concepts.

    The research is based on two of America’s largest, fastest-growing, and most water-stressed metropolises: Los Angeles (2nd largest metro at 13.2 million people) and Houston (5th largest metro at 6.5 million people). Through iterative design and fluid dynamics modeling, the project will discover the optimal wetland designs that combine engaging landscape topography and hydrologic performance and illustrate them as design guidelines for planning and water agencies all over the United States. These guidelines will reconceptualize how landscape architectural design can impact the cultural imagination of wetland engineering.

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    MIT NORMAN B. LEVENTHAL CENTER FOR ADVANCED URBANISM - PROJECT PRIMER

  • INTRODUCTION

    Drivers for Change

    American cities face interrelated threats to their water systems: stormwater pollution (causing impairment in 121,000 miles of the nation’s rivers), flooding (costing $2.4 billion in 2014 alone), and water scarcity (expected in 40 states within the next 10 years).1 [Figure 1] The increase in these threats is partly the result of having lost half of the nation’s wetlands since colonization.2 In some places, the loss is often dramatic: over 95 percent loss in Los Angeles County, and 30 percent in Harris County (metro Houston) between 1992 and 2010 alone.3

    Historically, the response to these threats has been to eliminate natural systems and build costly engineered infrastructure predicated on the false notion that nature could be predicted, controlled, and ordered. [Figure 2] In doing so, the result has often been exacerbated risk in cities, instead of the assured protection that was originally intended.4 As the mistakes of the past amount to greater vulnerability, cities need a new paradigm of water infrastructure that responds to the real patterns of nature, which often remain unpredictable and uncertain in spite of our scientific and technological advancements.

    Today’s cities face unprecedented urban flooding that have led many to rethink the role and value of soft infrastructures such as wetlands to capture and treat stormwater. Cities are building constructed wetlands for capturing stormwater, an infrastructure type that began in the 1980s as a derivative of agricultural wastewater treatment wetlands created by civil engineers.5 The wastewater engineering origin of the stormwater wetland remains visible today in its utilitarian aesthetic and function. Even as landscape architects have become more involved in such projects, the design and physical manifestation of stormwater wetlands remains

    FIGURE 1

    Buffalo Bayou during the major April 2016 floods in Houston with downtown in the background. PC: Elliott Blackburn, CC BY-NC-ND 2.0

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    MIT NORMAN B. LEVENTHAL CENTER FOR ADVANCED URBANISM

  • an engineering-based product driven by regulatory stormwater rules and the urban hydrology technocracy.6 Stormwater wetlands are typically conceived as site specific solutions, designed to retroactively alleviate a small scale problem without solving larger systemic watershed problems.7

    At the scale of the regional watershed, stormwater wetland networks can be conceptualized as public landscapes. Our project seeks to create practical design guidance for stormwater wetlands, to be used by cities to reconceptualize how water is controlled, managed, treated, and used as a public landscape resource and contributes to urban water resiliency.8 This project represents an opportunity to develop stormwater wetlands as resiliency infrastructure for cities to improve ecosystem services, alleviate water shortages through water re-use, flood control, and open space. In doing so, a wetland landscape becomes an inseparable part of the city’s structure.9

    General Approach on Methodology

    The project will be grounded in an understanding of the water challenges, environmental conditions, and geographic factors of Los Angeles and Houston. [Figure 3] This analysis will yield insights as to where water treatment, flood protection, and/ or groundwater recharge make sense in each metro area. A number of design iterations will be tested via physical fluid dynamics modeling and numerical modeling to determine performance. [Figure 4] Terraforming, landscape architectural design, and fluid mechanics engineering will merge in our working methods to yield new configurations of highly efficient wetlands.

    FIGURE 2

    The highly channelized and engineered Los Angeles River. PC: jondoeforty1, CC BY- NC-ND 2.0

    3Berger, Nepf, Guzmán, STRATEGIES FOR URBAN STORMWATER WETLANDS

    PROJECT PRIMERS

  • We will also explore ways to create a citywide wetland network that offers opportunities for recreation, resiliency features, economic activities, water re-use, conservation areas, and raised real estate values. Finally, the research will be summarized and translated into design guidelines that will articulate the principles behind the optimal designs and how they operate at the metropolitan scale.

    The project is based on the work of Professors Alan Berger and Heidi Nepf in designing agricultural wastewater treatment wetlands for the Pontine Marshes in Italy.10 The large-scale urban context of wetland design and application to stormwater comes from Celina Balderas Guzmán’s Masters thesis at MIT.11

    Background, Purpose, and Intended Audience

    The impetus for the project comes from a rejection of the traditional disciplinary divide between engineering and design and the belief that outcomes can be more impactful with close collaboration. Although many designers and planners have talked about bridging this divide, and have conceptualized landscape as infrastructure, there remains a need to articulate more concretely how landscape infrastructure actually functions in a city at a large-scale and how multi-functionality can be embedded in a system.

    The design guidelines will provide useful illustrative visions for

    Figure 2: Los Angeles Spatial Analysis

    FIGURE 3

    Los Angeles GIS analysis of stormwater infrastructure, natural hydrologic network, watershed boundaries, soil conditions, rainfall patterns, floodplains, land use, existing open spaces, and vacant lands.

    FIGURE 4

    Physical testing in the Nepf Fluid Dynamics Lab.

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    MIT NORMAN B. LEVENTHAL CENTER FOR ADVANCED URBANISM

  • designers, planners, engineers, developers, and community organizations engaged in the design and construction of constructed wetlands. The project will also aid policymakers (EPA, state agencies, environmental non-profits) and city agencies (particularly public works departments) in making project decisions around stormwater and other water-based resiliency issues.

    CURRENT CHALLENGES & OPPORTUNITIES

    Conceptual Urbanism Challenges & Opportunities

    With both climate change and global urban growth coming to a head, stormwater will only grow as a problem in urbanized areas. Already, there are 700 cities in the United States with combined sewer systems that contribute stormwater pollution to natural water bodies.12 Municipal discharges, including combined sewer overflows, and stormwater runoff are identified as a source of impairment in roughly 121,000 miles of rivers and streams, 1.2 million acres of lakes, 8,000 square miles of bays and estuaries, 600 miles of coastal shoreline, 500 square miles of ocean, and 72,000 acres of wetlands nationally.13 Impairment of natural systems degrades ecosystem services that cities depend on.

    In eleven American mega-regions, approximately 73 million people live in 4,400 square miles of “urban stream deserts,” areas were streams have been entirely buried or removed.14 Not only does this finding reveal the highly compromised condition of the natural environment in urban areas, it also suggests that a massive amount of people would benefit from wetland infrastructure due to the public health and amenity benefits of natural open space.

    To date, cities have been addressing these issues through green infrastructure, such as swales, detention ponds, green roofs, and rainwater harvesting. Although cheaper than conventional engineered infrastructure, the benefits of green infrastructure are still unclear due to their small scale and piecemeal implementation.15

    Even with existing rainfall patterns in both Los Angeles and Houston, the high levels of imperviousness of urban watersheds means that large volumes of stormwater cannot be accommodated on available urban land at a