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The buildings, parking lots and roads that have spread across urban America in recent decades have likely aggravated the area's water shortfall, representatives of three national environmental groups said.
Asphalt and roofs send rainfall cascading into ditches and streams, rather than letting it percolate into the soil to replenish the groundwater. Groundwater not only feeds wells but also helps maintain a constant flow in streams and rivers, said Betsy Otto, director of watershed programs at American Rivers in Washington. The group released a report along with the Natural Resources Defense Council and Smart Growth America.
"Sprawl completely alters that natural flow of water," Otto said. "It's much like what happens when you pour water on a brick. Literally billions of gallons of water are being sent down the storm drain as a result of sprawling development."
The environmental advocacy groups estimated the amount of water lost to development in the country's 20 fastest-growing metropolitan areas. For example, the 207,000 acres developed in the Triangle area of North Carolina between 1982 and 1997 divert 9.4 billion to 21.9 billion gallons of water a year from the region's groundwater, according to the groups.
The environmentalists might be right, but no one has studied in detail the effect of development on the Triangle's water supply, said John Morris, head of the state Division of Water Resources. Scientists would have to factor in differences in soils, long-term changes in weather and the fact that some storm runoff is not lost but helps fill reservoirs, Morris said.
"It's clear that impervious surfaces and urban development have a big impact on how water behaves," he said. "The difficulty is just figuring out what the quantitative impact of that is on a big river basin."
The environmental groups acknowledged that their calculations were blunt and that many factors could alter the effects of development on groundwater. For example, they said, more water runs off lawns than forests, but frequent irrigation of lawns could help recharge groundwater.
The groups hope their report, "Paving Our Way to Water Shortages," will inspire government or university researchers to look more closely at how development affects water supply, said Deron Lovaas, deputy director of the smart growth program at the Natural Resources Defense Council. Ultimately, though, they say local governments should concentrate development to reduce the amount of pavement and rooftops covering the land.
That conclusion drew fire from the National Association of Home Builders, which called reporters nationwide late Wednesday to offer its critique. Clayton Traylor, a senior vice president, said the environmental groups didn't account for the effect of regulations designed to curb storm run-off and ignored the fact that denser development can also prevent water from filtering into the ground.
"No matter what problem they identify, what kind of quasi study they do, the solution is always the same: We need more regulation of land use, we need to force density, we need to curb development," Traylor said. "It's awfully predictable."