City Parks, Clean Water, Green Infrastructure, Part I

Alewife Reservation image: MWH Global
Alewife Reservation
image: MWH Global

Many of you may know The Trust for Public Land (TPL) as an organization devoted to the protection and support of the places people care about and the creation of “close-to-home parks” — particularly in and near cities, where 80 percent of Americans live. Through its Center for City Park Excellence (CCPE), TPL also explores the many issues that affect the success of urban areas’ park systems. CCPE’s most recent publication, City Parks, Clean Water: Making Great Places Using Green Infrastructure, looks at the many ways that parks can help with the control of urban stormwater.

Using case studies, data tables, and interviews with national experts, the report explores both new and existing parks, including in-depth studies of water-smart parks in Atlanta, Birmingham, Alabama, Cambridge, Massachusetts, New York, and Shoreline, Washington. The following is the first installment of a two-part series excerpted from the report.

Lisa Nabor Cowan, ASLA, Sustainable Design & Development PPN Officer, Principal, Studioverde

Part I: City Parks, Clean Water, Green Infrastructure

The effort to clean our nation’s waterways has been underway, with increasing strength, for more than 50 years. Great progress has been made, particularly against pollution from untreated sewage and unregulated factories. Rivers no longer catch on fire, oil slicks are a rarity, and most raw discharge pipes have been eliminated. But in cities there remains work to be done, with most urban waterways still not clean, not swimmable, not safe for fishing, and sometimes not even pleasantly boatable.

The primary culprit, as all landscape architects know, is pollution from runoff from paved surfaces – streets, sidewalks, driveways, parking lots, roofs, patios, plazas, even playgrounds that quickly shed the rain. The solution is to hold back the water where it hits, slow it down so that the destructiveness of erosion and contaminants are controlled, and clean it before it reaches a waterway.

With two different methods of doing this – using giant holding tanks for storage or a natural, spongier approach for infiltration – the U.S. is at a critical decision point in how it will allocate billions of dollars in the coming decades.

If we go with the soil-based, green infrastructure approach in urban areas, we have to be realistic about the opportunities and possibilities. Do cities have enough unbuilt land to capture water on the surface? After all, in cities, water-capturing surfaces are often somewhat scarce, located primarily in only four places: in private yards, on campuses of various types, alongside public roadways, and within public parks.

PS 261 before renovations. The Trust for Public Land converted the asphalt schoolyard at Brooklyn’s Public School 261 into a greenspace open to the public after school and on weekends. image: Mary Alice Lee
PS 261 before renovations. The Trust for Public Land converted the asphalt schoolyard at Brooklyn’s Public School 261 into a green space open to the public after school and on weekends.
image: Mary Alice Lee
Renovations at Brooklyn’s P.S. 261 added an artificial turf field, rain gardens to absorb runoff, a gazebo with green roof, rain barrels for irrigation water, and permeable paving. All told, the half-acre park can capture about 500,000 gallons of stormwater annually. image: Pedro Diez
Renovations at Brooklyn’s P.S. 261 added an artificial turf field, rain gardens to absorb runoff, a gazebo with green roof, rain barrels for irrigation water, and permeable paving. All told, the half-acre park can capture about 500,000 gallons of stormwater annually.
image: Pedro Diez

Parks already play a significant role in absorbing stormwater since they comprise of 2 percent, 5 percent, 10 percent, or even more of every city’s land area. Right now most of these lands capture only the rain and snow that fall directly on them, but they could theoretically do much more. They are potentially the sites of great new “water-smart parks” that treat runoff as a multiple-benefit asset.

Of course, urban parks have numerous other benefits to residents, some of which may not be fully compatible with absorbing and holding large quantities of water. Could fields become too soggy for sports and recreation? Might playgrounds lose too much space to fenced-off rain gardens? Some skeptics worry that rain gardens might deteriorate into an unattractive landscape while others fear an increase in mosquitoes. Still others fret that pervious paving could buckle under heavy usage. Many of these theoretical worries never come to pass, but they can also represent emotional and political roadblocks to moving forward. The opportunities for cost-saving, win-win solutions are enormous, but there may also be a risk of unanticipated side-effects. The goal is to maximize benefits while minimizing drawbacks, and to use the synergies to reduce costs.

One organization deeply involved at the intersection of parks and stormwater management is The Trust for Public Land (TPL). TPL consults with cities to reduce flooding, maps opportunities to counter the effects of rapid urbanization that has paved formerly porous land, and shows citizens how to get involved in the political process. TPL has physically built water-absorbing parks, from New York and Philadelphia to San Francisco and Los Angeles, and is an official partner of the U.S. Environmental Protection Agency (EPA) through the Green Infrastructure Collaborative, a learning alliance to share best practices.

TPL’s most recent addition, City Parks, Clean Water: Making Great Places Using Green Infrastructure, is a major study which shines a light on the successes and challenges of water-smart parks. It looks both at the technologies and the political issues involved in these techniques, and some of the report’s highlights are summarized here.

Why Parks?

Parks have been capturing stormwater from the beginning, often unintentionally through vegetation and porous soils, sometimes purposefully through such large-scale projects as Frederick Law Olmsted’s 1885 redesign of Boston’s Muddy River to deal with festering mudflats and flooding. But the movement ebbed and flowed, mirroring the changing philosophies of water handling over the decades, and for much of the 20th century the dominant strategy was to move water downstream as quickly as possible. That anti-ecological approach is now being upended, and a new generation of stormwater capture techniques are being pioneered, with some city park agencies leading the way. In a 2014 survey by The Trust for Public Land, 82 percent of responding agencies reported that they have created at least one stormwater capture facility, and the collective acreage of these early efforts are already in the thousands.

A multi-agency partnership in Cambridge, Massachusetts converted the underutilized Alewife Reservation to a large engineered wetland (which can absorb and clean 3 million gallons of runoff per storm) with enhanced recreational opportunities, including a bike path and long boardwalks. image: MWH Global
A multi-agency partnership in Cambridge, Massachusetts converted the underutilized Alewife Reservation to a large engineered wetland (which can absorb and clean 3 million gallons of runoff per storm) with enhanced recreational opportunities, including a bike path and long boardwalks.
image: MWH Global

The Different Goals

Parks and clean water are both public goods of the highest order; combining the two offers great opportunities for collaboration. In the simplest terms, water management requires space, and parkland is a leading resource of space in cities. Conversely, park maintenance requires money, and water utilities have a steady, predictable source of revenue through residential and business water fees.

Nevertheless, there are challenges that sometimes interfere with partnering. For one thing, stormwater has a complex range of impacts, and the techniques for dealing with those impacts are not easy to carry out, or even to explain to the public. For another, there are many different kinds of park users who have vastly different opinions about what makes a park great and what degrades it.

From the perspective of park agencies, there are two major goals that can be furthered by collaboration with stormwater utilities – improving ecological function and reducing costs. These can take several forms:

  • Contributing to improved park hydrology: In hilly cities, water racing into parks can not only flood playing fields and undermine trees, but also wash out streams and dump sediment downstream. Since every new swale and detention pond slows the runoff and reduces the burden on waterways and treatment plants, it may be cost-effective for stormwater utilities to help pay for these improvements on parkland. Moreover, these features can serve as attractive, ecological alternatives to the wasteful and dangerous practice of putting drains in the middle of grassy recreational fields.
  • Saving money on irrigation: Just like private citizens, many park agencies have to pay for water. (Even if the bill is picked up by the government at large, it’s still a cost to taxpayers.) This expense is often substantial – in San Diego it came to more than $12 million in 2013 and $10 million in Chicago. Even where fees are lower, the tab is rising rapidly. Beyond that, some agencies pay a stormwater or drainage fee to a sewer agency based on the size of their property holdings and the percent of their impermeable land. Therefore, the less water sent down the drain, the more water is available to feed the parks, and the more funds are freed up for programming and other needs. Even better are situations where park departments are financially rewarded for saving water. According to a 2014 Trust for Public Land survey, about fourteen percent of park agencies, including those in Seattle, Minneapolis, and Cincinnati, are given a rebate for water that parks treat and manage while keeping it out of the sewer system. This arrangement gives the agencies an additional financial incentive to creatively modify some of their parkland.
PS 261: children playing with the new rain garden and gazebo in the background. image: Pedro Diez
PS 261: children playing with the new rain garden and gazebo in the background.
image: Pedro Diez

by Peter Harnik, Director and Abby Martin, Assistant Director, The Trust for Public Land’s Center for City Park Excellence, based in Washington, D.C.

Part II scheduled to be published on July 5, 2016.

One thought on “City Parks, Clean Water, Green Infrastructure, Part I

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