Download pdf - STRATEGIES FOR URBAN STORMWATER WETLANDS · STRATEGIES FOR URBAN STORMWATER WETLANDS Alan M. Berger, Heidi Nepf, Celina Balderas Guzmán Project Contributors Tyler Swingle, Department

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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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 reasonable cost. Moreover, the seasonality of rainfall in some areas means that long dry periods will harm wetland plants and diminish the capacity of the wetland to treat stormwater when it is available. Climate change will exacerbate both of these problems by lengthening and intensifying wet or dry cycles.

Historically, people disdained wetlands out of the belief that they spread disease and impeded travel, agriculture, and urban construction. Meanwhile, their benefits remained unknown or ignored. For these reasons, many people today continue to hold negative perceptions of wetlands, especially when a wetland does not conform to public aesthetic


PROJECT PRIMERS

preferences for landscapes that look healthy and complex, but also orderly and ‘natural.’16 Achieving these attributes requires more than attending to the engineering performance of a wetland; successful wetland projects need careful landscape design and regular maintenance to earn public acceptance.

Furthermore, cities face a learning curve with operating and maintaining landscape infrastructure. The skills, equipment, and knowledge required to care for storm pipes and treatment plants is different than those required to care for dynamic wetland landscapes. Cities have run on the former model for many decades. Yet because no city yet relies on green infrastructure at a large scale, little precedent or knowledge exists for the latter. Although cities are interested in stormwater wetlands, they are also hesitant to build such projects because of negative perceptions and the economic and political risk involved with building a new infrastructural type.

Organizational and Institutional Challenges

With all natural systems— water being no exception— there is a mismatch between administrative and natural boundaries, necessitating regional cooperation that often does not exist. Moreover, multiple agencies may have oversight over the same issue or geography. For example, the project to restore the 600-acre Ballona Wetlands in Los Angeles is an effort by three state agencies and will involve multiple permits from other state and federal agencies, as well as community buy-in. The multiplicity of stakeholders, while perhaps useful in keeping checks and balances, has also delayed the project for over a decade.

Funding mechanisms for infrastructure projects are fewer as the need becomes greater. American cities need $298 billion over the next 20 years for wastewater and stormwater management and capital investment.17 But federal funding sources for water infrastructure are diminishing. The Environmental Protection Agency (EPA) faced a budget cut that will largely be achieved by a $581 million reduction in two key water infrastructure funds.18 Meanwhile, regulations are tightening around stormwater and CSOs. Cities will have to make strategic investments in order to meet higher standards at a lower cost.

Once projects are constructed, there may be further challenges with maintenance and operations as they may fall under the prevue of various agencies and heavy regulation. Also, wetland projects may undergo an extensive period in their inception where their performance is suboptimal.19 Obtaining extra resources to stabilize performance and gaining public acceptance become political difficulties in this period.

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ADVANCED URBANISM MODELS

Principles & Theories

The overarching principle is the seamless integration between landscape architectural design and fluid mechanics engineering, carried out by the simultaneous development of hydrologic function, design ideation, and recreational programming, in a replicable wetland cell. If successful, urban wetlands can be used to address water resiliency issues and open space needs of cities simultaneously in the age of climate-change induced flooding.

Precedents

Currently, there are no precedents for wetland projects that demonstrate the above principles. Wetland projects led by engineers, such as the South Los Angeles Wetland Park, offer a conventional wetland design with a perimeter trail. Although the performance of the wetland is closely tracked, it does need to be supplemented with drinking water in the dry season, which has made the project controversial. Wetland projects led by designers, such as Turenscape’s large-scale wetland projects in China, offer a lot of urban amenities and supposedly offer flood protection and water treatment benefits, however, the performance of these wetlands is not tracked.

The closest precedent for this project is the work of Frederick Law Olmsted in the nineteenth century, who brilliantly merged performance, program, and aesthetics into his landscape projects, including the Back Bay Fens in Boston and Central Park in New York City. However, there is one important difference between the work of Olmsted and this project: Olmsted hid the performative aspects of his landscape through his English-derived naturalistic aesthetic.20 A new aesthetic can be found that is not wholly imitating nature nor seeking to hide the performative functions of the landscape. [Figure 5]

FIGURE 5

Plan of Olmsted’s Back Bay Fens in Boston. Source: Olmsted Archives, National Park Service


PROJECT PRIMERS

Project Vision & Goal

The vision of this project is to illustrate the full potential of a system of urban constructed wetlands to be multi-functional infrastructure that contributes to the resiliency of a region and to a city’s urban amenities. The design guidelines will feature a catalog of design options that are dependent on resiliency goals, urban programming needs, and local environmental conditions.

IMPLEMENTING THE STRATEGIC VISION

Besides land acquisition and regulatory challenges, cost and public acceptance are two key implementation issues. Complex landforms can be costly to build, however, if all positive externalities were calculated they may outweigh costs.21 Public acceptance depends on perceptions of wetlands. Although they have been improving over time, studies have revealed that the public has certain preferences that might not be well matched to ecological performance.22

Wetland typologies will be developed according to a set of programmatic requirements (recreation, agriculture, conservation) matched with stormwater goals (water treatment, flood protection, and/ or groundwater recharge). The stormwater goal for a site depends on climate, soil conditions, location in the hydrologic network (upstream versus downstream), and watershed and site size.

Buffalo Bayou SiteHouston, TexasSite Area: xx acresLow Flow: xx cfsFirst Flush: 1 inch85% storm: xx cfs

Taylor Yard SiteLos Angeles, CASite Area: 45.66 acresLow Flow: 1.19 cfsFirst Flush: 1 inch85% storm: 7230 cfs

Watershed Watershed

LA River

to Downtown

to Downtown

LA River

TaylorYardTaylorYard

Buffalo Bayou

Buffalo Bayou

Downtown

Downtown

Brays Bayou

Brays Bayou

FIGURE 6

Potential demonstration areas in Los Angeles and Houston.

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Potential Demonstration Areas [Figure 6]

- Los Angeles: Taylor Yard (Los Angeles River) and spreading ground sites (San Gabriel River)

- Houston: Buffalo Bayou downtown site and northeastern residential sites

The building of a constructed wetland infrastructure system would be subject to local and federal stormwater rules. At the municipal level, cities often have requirements for site-level stormwater management, such as capturing one inch of water and retaining it for twenty-four hours. At a federal level, all cities are subject to National Pollutant Discharge Elimination System rules that regulate stormwater runoff.


PROJECT PRIMERS

Endnotes

1 “National Water Quality Inventory: Report to Congress” (Environmental Protection Agency, 2004), http://water.epa.gov/lawsregs/guidance/cwa/305b/upload/2009_05_20_305b_2004report_report2004pt1.pdf; United States Government Accountability Office, “Freshwater: Supply Concerns Continue, and Uncertainties Complicate Planning,” May 2014; National Oceanic and Atmospheric Administration, “United States Flood Loss Report- Water Year 2014,” n.d., http://www.nws.noaa.gov/hic/summaries/WY2014.pdf.

2 Thomas E Dahl and U.S. Fish and Wildlife Service, Status and Trends of Wetlands in the Conterminous United States 2004 to 2009 (Washington, D.C.: U.S. Dept. of the Interior, U.S. Fish and Wildlife Service, Fisheries and Habitat Conservation, 2011), 16.

3 “The Greater Los Angeles County Open Space for Habitat and Recreation Plan” (Greater Los Angeles County Integrated Regional Water Management Plan, June 2012), 17, http://www.ladpw.org/wmd/irwmp/docs/Prop84/GLAC_OSHARP_Report_Final.pdf; John S. Jacob et al., “Houston-Area Freshwater Wetland Loss, 1992-2010” (Texas Coastal Watershed Program, n.d.), http://tcwp.tamu.edu/files/2015/06/WetlandLossPub.pdf.

4 Jared Orsi, Hazardous Metropolis: Flooding and Urban Ecology in Los Angeles (Berkeley: University of California Press, 2004).

5 Celina Balderas Guzmán, “Strategies for Systemic Urban Constructed Wetlands” (Massachusetts Institute of Technology, 2013), 11, http://hdl.handle.net/1721.1/80907.

6 Ibid.; Andrew Karvonen, Politics of Urban Runoff: Nature, Technology, and the Sustainable City (MIT Press, 2011), http://www.jstor.org/stable/j.ctt5hhm9z.

7 See “Systemic Wetlands” chapter in Balderas Guzmán, “Strategies for Systemic Urban Constructed Wetlands,” 14, 97–105.

8 J.N Carleton et al., “Factors Affecting the Performance of Stormwater Treatment Wetlands,” Water Research 35, no. 6 (April 2001): 1552–62, doi:10.1016/S0043-1354(00)00416-4; Two examples of design guidelines: Thomas R Schueler and Anacostia Resoration Team, Design of Stormwater Wetland Systems: Guidelines for Creating Diverse and Effective Stormwater Wetlands in the Mid-Atlantic Region (Washington, D.C.: Anacostia Restoration Team, Dept. of Environmental Programs, Metropolitan Washington Council of Governments, 1992); This is an update to Schueler’s work: Karen Cappiella et al., “The Next Generation of Stormwater Wetlands” (Center for Watershed Protection, February 2008).

9 See “Systemic Wetlands” chapter in Balderas Guzmán, “Strategies for Systemic Urban Constructed Wetlands,” 97–104, 115; Momentum is building in cities to increase stormwater capture: Adam Nagourney, “Storm Water, Long a Nuisance, May Be a Parched California’s Salvation,” The New York Times,

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February 19, 2016, http://www.nytimes.com/2016/02/20/us/storm-water-long-a-nuisance-may-be-a-parched-californias-salvation.html; Monte Morin, “DWP to Unveil Plan to Capture Storm Runoff,” Los Angeles Times, June 25, 2015, http://www.latimes.com/local/california/la-me-stormwater-plan-20150625-story.html.

10 Peter Dizikes, “Using Plants to Purify Canal Water,” MIT News, April 7, 2010, http://news.mit.edu/2010/italy-water-0407.

11 Balderas Guzmán, “Strategies for Systemic Urban Constructed Wetlands.”

12 United States Environmental Protection Agency, “Greening CSO Plans: Planning and Modeling Green Infrastructure for Combined Sewer Overflow (CSO) Control,” March 2014, 5.

13 “National Summary of State Information | Water Quality Assessment and TMDL Information | US EPA,” accessed March 24, 2016, https://ofmpub.epa.gov/waters10/attains_nation_cy.control#prob_source.

14 Jacob A. Napieralski and Thomaz Carvalhaes, “Urban Stream Deserts: Mapping a Legacy of Urbanization in the United States,” Applied Geography 67 (February 2016): 129–39, doi:10.1016/j.apgeog.2015.12.008.

15 Committee on Reducing Stormwater Discharge Contributions to Water Pollution, National Research Council, Urban Stormwater Management in the United States (Washington, D.C.: The National Academies Press, 2009), 1.

16 Meredith Frances Dobbie, “Public Aesthetic Preferences to Inform Sustainable Wetland Management in Victoria, Australia,” Landscape and Urban Planning 120 (December 2013): 188, doi:10.1016/j.landurbplan.2013.08.018; See “Histories of Wetlands in the United States” chapter in Balderas Guzmán, “Strategies for Systemic Urban Constructed Wetlands,” 17–32.

17 “CWNS 2008 Report to Congress | Clean Watersheds Needs Survey | US EPA,” accessed January 25, 2015, http://water.epa.gov/scitech/datait/databases/cwns/2008reportdata.cfm; American Society of Civil Engineers, “2013 Report Card For America’s Infrastructure,” 2013, http://www.infrastructurereportcard.org.

18 The two key federal sources are the State Clean Water Revolving Fund and the Drinking Water Revolving Fund. Patrick Ambrosio, “President Proposes Cut To EPA Funding for Fiscal Year 2015,” Bloomberg, March 6, 2014, http://www.bloomberg.com/news/2014-03-06/president-proposes-cut-to-epa-funding-for-fiscal-year-2015.html; OCFO US EPA, “FY 2015 Budget,” Overviews and Factsheets, accessed January 25, 2015, http://www2.epa.gov/planandbudget/fy2015; Ronald White, “Congress Slashes EPA Budget Again Despite Strong Public Support for Strengthening Health Protections | Center for Effective Government,” accessed January 25, 2015, http://www.foreffectivegov.org/blog/congress-slashes-epa-budget-again-despite-strong-public-support-strengthening-health-protection.


PROJECT PRIMERS

19 Shahram Kharaghani, Conversation about stormwater projects in the city of Los Angeles with the Department of Sanitation Watershed Protection Program Manager, November 10, 2015.

20 1. Anne Whiston Spirn, “The Poetics of City and Nature: Towards a New Aesthetic for Urban Design,” Landscape Journal 7, no. 2 (1988): 108–26.

21 M.J. Vanaskie, R.D. Myers, and J.T. Smullen, “Planning-Level Cost Estimates for Green Stormwater Infrastructure in Urban Watersheds,” 2010, 547–58, doi:10.1061/41099(367)48; Carolyn Kousky et al., “Strategically Placing Green Infrastructure: Cost-Effective Land Conservation in the Floodplain,” Environmental Science & Technology 47, no. 8 (April 16, 2013): 3563–70, doi:10.1021/es303938c; See the chapter “The Cost & Value of Constructed Wetlands,” Balderas Guzmán, “Strategies for Systemic Urban Constructed Wetlands,” 107–13.

22 Dobbie, “Public Aesthetic Preferences to Inform Sustainable Wetland Management in Victoria, Australia”; Meredith Dobbie and Ray Green, “Public Perceptions of Freshwater Wetlands in Victoria, Australia,” Landscape and Urban Planning 110 (February 2013): 143–54, doi:10.1016/j.landurbplan.2012.11.003; R.c. Rooney et al., “Replacing Natural Wetlands with Stormwater Management Facilities: Biophysical and Perceived Social Values,” Water Research 73 (April 15, 2015): 17–28, doi:10.1016/j.watres.2014.12.035.

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