When you think of “green” cities, Detroit and Philadelphia don’t usually spring to mind.
But they and a dozen others have kept 10 trillion gallons of polluted water out of their waterways and overtaxed sewer systems by using greener infrastructure, a new report shows.
|The City of Philadelphia unveiled its first street made of pervious pavement in February and is on its way to transforming 34 percent of its impervious surfaces.|
By reducing the amount of impervious pavement, tightening stormwater regulations and other measures, the 14 cities are leading the way in stopping rain where it falls—sharply reducing runoff and sewage overflows and saving a great deal of money, reports Rooftops to Rivers II: Green Strategies for Controlling Stormwater and Combined Sewer Overflows, just released by the Natural Resources Defense Council.
The 133-page report discusses the significant problems caused by stormwater runoff, which carries pollution to rivers, lakes, and beaches and causes sewage system overflows. The analysis details infrastructure changes and other measures taken by 14 cities—yes, including Philadelphia and Detroit—that have captured trillions of gallons of water.
“Cities of all sizes are recognizing that green infrastructure—which stops rain where it falls—is the smartest way to reduce water pollution from storms,” said Karen Hobbs, NRDC senior policy analyst.
“And the extreme weather we’ve seen in much of the country this year—from drought to floods and hurricanes—drives home the need for smarter solutions to our water woes.”
The 14 cities featured in the report are all rated on a six-point “Emerald City Scale” that identifies the primary actions that NDRC says every city can undertake to maximize their green infrastructure investment.
|Pervious concrete is a mixture of cement paste and large aggregate, with little or no sand. The mix allows rain water to permeate to the sub-base of the concrete slab and return to the earth.|
Leading the green pack is Philadelphia, which is pursuing all six measures. Scoring a five out of six were Milwaukee, WI; New York, NY; Portland, OR; Syracuse, NY; and Washington, D.C. Notching four points each were Toronto, Ontario, and Aurora, IL. Three-point cities were Chicago, IL; Kansas City, MO; Nashville, TN; and Seattle, WA. Pittsburgh, PA, and the Detroit metro area each scored one point.
The Emerald City measures include:
• A long-term green infrastructure plan for the city;
• A retention standard;
• A requirement to reduce existing impervious surfaces using green infrastructure;
• Incentives for private-party action, guidance or other assistance in deploying green infrastructure; and
• A dedicated funding source.
Beyond Holding Tanks
Unlike paved and other impermeable surfaces, green infrastructure stops runoff and the pollution it carries from the start, by capturing rainwater and either storing it for future use or letting it filter back into the ground. Examples include permeable pavement, green roofs, and street trees.
The City of Philadelphia has been using pervious pavement in a variety of projects since 2005 and plans to transform 34 percent of the city’s impervious surfaces into “greened acres.”
This year, the city unveiled its first porous asphalt street. Porous asphalt looks almost identical to conventional but includes voids or spaces that allow water to pass through the material. A layer of stone underneath provides temporary storage for water as it slowly percolates into the ground, rather than running off into storm drains, sewer systems, basements and waterways.
Pervious pavement can be used for streets, parking lots, walking paths, sidewalks, and similar applications. Extremely dense urban areas have used it in redevelopment, since it treats and stores stormwater without consuming extra land, according to Stormwater PA.
The NRDC report details how green infrastructure is frequently more cost-effective than pipes, holding tanks and other traditional approaches to addressing runoff.
The City of Philadelphia estimates that a traditional approach to its sewage overflow problems would have cost billions more than its state-approved green infrastructure plan.
What Green Means
Among the initiatives highlighted in the report:
• Pittsburgh, PA, whose 4,000 miles of sewer pipes and 450 sewer overflow structures release 22 billion gallons of untreated municipal waste into surrounding waters every year, now requires development sites larger than 10,000 square feet to retain the first inch of rainfall from any storm onsite. Public projects must retain 1.5 inches of rainfall on site.
• Since 2003, Toronto, ON, Canada, has been following a 25-year, $1 billion Wet Weather Flow Master Plan to eliminate the adverse impacts of stormwater runoff.
• Kansas City, MO, created a stormwater utility in 1999 that assesses fees based on the size of a property’s impervious surface area.
The city has also broken ground on the 100-acre Middle Blue River Basin Pilot Project, the nation’s largest focused installation of green infrastructure as the sole control for combined sewer overflows.
• Indianapolis, IN, has completed a Green Infrastructure Master Plan to meet the terms of a federal consent decree that requires the city to reduce sewer overflows. Cleveland and Cincinnati, OH, facing similar decrees, are considering similar measures.
• A Minneapolis, MN, stormwater ordinance requires public and private development sites of one acre or more to include on-site stormwater management.
• Jacksonville, FL, is developing a guidance manual for developers, architects, engineers, and others seeking permitting specifications for green infrastructure construction.