City parks, clean water Making great places using green infrastructure City parks, clean water Making great places using green infrastructure The Trust for Public Land March 2016 Printed on 100% recycled paper. ©2016 The Trust for Public Land. The Trust for Public Land creates parks and protects land for people, ensuring healthy, livable communities for generations to come. Our Center for City Park Excellence helps make cities more successful through the renewal and creation of parks for their social, ecological, and economic benefits to residents and visitors alike. tpl.org Table of contents Introduction ..........................................................................................................................................5 The problem .........................................................................................................................................8 The different goals ...........................................................................................................................10 The different solutions and how they actually work ..............................................................18 Design considerations for success ..............................................................................................30 Staying involved ................................................................................................................................33 Negotiating between different uses of a park..........................................................................37 Who pays, who benefits, and how are costs accounted? .....................................................41 Conclusion ..........................................................................................................................................47 Acknowledgements .........................................................................................................................48 Case Studies Historic Fourth Ward Park, Atlanta .....................................................................................................11 Alewife Stormwater Wetland, Cambridge, Mass. ...........................................................................16 Railroad Park, Birmingham .................................................................................................................21 Cromwell Park, Shoreline, Washington .............................................................................................26 P.S. 261, Brooklyn, New York ..............................................................................................................28 Boxes Glossary: some key terms ...................................................................................................4 Box 1: Green infrastructure and the Environmental Protection Agency .....................................................................................6 Box 2: Public parkland as percent of city area .............................................................................7 Box 3: Parkland designed for flooding .........................................................................................9 Box 4: Selected park agency water bills .....................................................................................14 Box 5: Stormwater capture — acres and methods used ...........................................................19 Box 6: Stormwater control measures installation and maintenance costs per acre ......................................................................................20 Box 7: Pervious pavement .............................................................................................................24 Box 8: Understanding soils ...........................................................................................................31 Box 9: What about brownfields? ..................................................................................................36 Box 10: The cost of underground storage projects to hold combined sewer overflows ......................................................................................41 Box 11: Size of stormwater parks and years to complete ...........................................................42 Box 12: Cost of stormwater parks and facilities ...........................................................................43 Box 13: When stormwater agencies take the lead ......................................................................44 Glossary: some key terms Bioretention Phytoremediation The process by which vegetation and soil Technique for cleaning stormwater naturally slow down or capture sediment, runoff and soils, relying on trees and nutrients, oils, and other pollutants plants to take up and hold or neutralize commonly found in stormwater runoff. pollutants, especially heavy metals or Bioretention areas are sometimes called nutrients. “rain gardens.” Rain gardens Combined sewer system Sunken, carefully vegetated areas with A network of pipes that carry a combi- permeable soil that hold and clean nation of domestic sewage, industrial runoff before it percolates into ground- wastewater and stormwater runoff to water or evaporates. a municipal treatment facility. In dry Retention and detention ponds weather the system works well, but Two contrasting stormwater the huge volume from a rainstorm or management facilities. Retention ponds snowmelt may overwhelm the capacity, have hard bottoms and retain storm- and untreated commingled wastewater water for later reuse; they are usually may get dumped directly into a waterway wet, even in dry periods. Detention or ocean. The discharges are called ponds have soft bottoms and detain “combined sewer overflows,” and the stormwater so that it can percolate down point where the wastewater enters a to an aquifer; in dry periods they are dry. waterway is a “combined sewer outfall.” Most older cities still have neighborhoods Structured soils with combined sewer systems and are Artificially created mixtures that provide under orders to separate them. better drainage, more load strength, or other benefits over existing soils. Consent decree A negotiated settlement between the Swales Environmental Protection Agency, state Soft-bottomed, grassy, linear channels regulatory agency, and municipality (or that direct stormwater runoff to rain sewer district) that provides a framework gardens, holding basins, or, sometimes, for local compliance with pollution the sewer system. Vegetated swales, regulations under the Clean Water Act. also known as “bioswales,” are more The resulting long-term control plan thickly planted and can partially treat charts steps to bring water quality into flowing stormwater by removing silt and compliance, often over several decades. pollutants. Permeable pavement Wetlands Engineered surfaces designed to function Watery, low-lying areas that slow and like standard construction materials while hold stormwater, filter out contami- still allowing stormwater to pass into the nants, and soften the impact of storm ground. Materials can include asphalt, surges. Also known as swamps, bogs, or concrete, and spaced paver blocks. marshes. 4 city parks, clean water: making great places using green infrastructure Introduction The effort to clean our nation’s waterways has devices to capture and convey runoff. In some been underway, with increasing strength, for documents, “green infrastructure” refers to more than 50 years (see Box 1). Great progress the regional-scale preservation of large swaths has been made, particularly against pollution of conservation lands, but in this report the from untreated sewage and unregulated fac- term is limited to specific, small-scale man- tories. Rivers no longer catch on fire, oil slicks agement techniques to preserve and restore are a rarity, and most raw discharge pipes have the natural capacity of land to slow, filter, and been eliminated. But in cities there remains absorb stormwater. work to be done, with most urban waterways still not clean, not swimmable, not safely fish- To make the decision between gray and green able, sometimes not even pleasantly boatable. the nation has to be realistic about the oppor- tunities and possibilities. Do both approaches The primary culprit is pollution from rain and work equally well? Is one less expensive? snow runoff. Can they be combined? Are residents willing to put up with years of tunneling under their The problem is not the rain and snow itself. neighborhoods? Conversely, does the city The problem is too many paved surfaces — have enough unbuilt land to capture water on streets, sidewalks, driveways, parking lots, the surface? roofs, patios, plazas, even playgrounds that quickly shed the rain. The solution is to hold In cities, water-capturing surfaces are often back the water where it hits, slow it down somewhat scarce, located primarily in four so that the destructiveness of erosion and places: in private yards, in campuses of various contaminants is controlled, and clean it before types, alongside public roadways — and within it reaches a waterway. But with two different public parks. methods of doing this — using giant holding tanks for storage or a natural, spongier ap- Parks already play a significant role in absorb- proach for infiltration — the U.S. is at a critical ing stormwater since they comprise 2 percent, decision point in how it will allocate billions of 5 percent, 10 percent or even more of every dollars in the coming decades. Will we spend