When it rains, stormwater runoff is captured in city storm sewers and eventually empties into rivers, ports and other waterways. Communities use many strategies to prevent, control and treat stormwater. These strategies include reducing impervious surfaces on driveways and sidewalks and creating drought-resistant landscapes to hold and filter water.
The objective is to get the land to act like a sponge and soak up the rainwater and return it to the ground rather than divert it to a sewer. Limiting the flow of stormwater reduces the amount of polluted runoff reaching waterways and prevents treatment facilities from being overwhelmed by combined sewer overflows.
Now urban designers are looking at ways to design and build cities like sponges for another reason – to capture water to counter drought conditions. A recent Morning Edition report on National Public Radio (NPR) reported on efforts to respond to water scarcity in Los Angeles by capturing rainwater and turning it into water for drinking and irrigation.
Woodbury University’s Arid Lands Institute (ALI) is helping developers in the city find the best spots for water to percolate into the ground. An experimental project in one neighborhood is placing bioswales along sidewalks. These are gullies filled with drought-resistant plants. Water collects in the bioswales and filters down into cisterns that are buried below the street. According to ALI, an education, research and outreach center dedicated to design innovation in water-stressed environments, in an average rain year, a city block puts enough water into the ground for approximately 30 families for a year.
Another consideration is the design of roofs. The peaked roof is practical in areas where snow falls. Experts are suggesting that roof designs in arid areas should have a wide mouth that is open to the sky and built to catch rain.
Desert cities may be the first “sponge” cities, but others are likely to follow. The Natural Resource Defense Council’s Climate Change, Water, and Risk report found that 1,110 U.S. counties – one-third of all counties in the lower 48 states – will face higher risks of water shortages by mid-century due to climate change.
Cathy Spain is a National League of Cities Service Line Warranty Program Advisor and President of The Spain Group. She works with private companies and nonprofits to design, analyze and promote local government programs. She’s held senior management, research and lobbying positions at the National League of Cities, Government Finance Officers Association, Public Risk Database Project and the New York State Assembly.