WASHINGTON -- A study released today by the national conservation group American Forests found that a 20 percent loss of trees and other vegetation in the Atlanta metropolitan region produced a 4.4 billion-cubic foot increase in stormwater runoff. It would cost at least $2 billion to build containment facilities capable of storing the excess water, according to officials.
Between 1986 and 1993, the displacement of trees by development caused stormwater runoff to increase on a net total of approximately 1.2 million acres. That number would have been higher had it not been for improved tree cover that decreased runoff on approximately 900,000 acres. Natural elements of the landscape, such as trees and vegetation, slow the movement of stormwater, lower the total runoff volume, and reduce costly flooding.
"We found that removing natural vegetation and replacing it with manmade structures has a high cost. That makes a strong argument for incorporating natural systems into the decision-making process and finding new ways to build cities," said Gary Moll, vice president for urban forestry at American Forests and study coordinator.
The study, sponsored by the Turner Foundation, builds upon American Forests' pioneering Urban Ecological Analysis of the 10-county Atlanta region. American Forests used its proprietary CITY green Geographic Information System (GIS) software to map and analyze the urban ecosystem.
The study used engineering formulas developed by the Natural Resource Conservation Service to calculate the stormwater volume for a two-year, 24-hour storm event. The cost of building stormwater retention ponds ranges from $.17 to $17.00 per cubic foot. American Forests researchers based their calculations on a conservative figure of $.50.
"The actual cost will vary depending upon location and can be calculated using more detailed analysis," said Moll. "Nonetheless, what we have here is a clear indication of the magnitude of the value of vegetation in stormwater management."
The base map, covering 5.3 million acres, can be used to make future analyses of specific areas in the Atlanta region. One such area, the city of Chamblee, was chosen for more detailed analysis. A 44 percent decrease in its vegetation produced an increase in stormwater runoff that would require containment facilities costing approximately $29 million.
"Thanks to hi-tech tools such as City green, every community can determine the value of its local ecosystem and use that information for community development," said Moll. How to do that will be the theme of the 8th National Urban Forest Conference, "Cities by Nature's Design," September 17-20 in Atlanta. Organizer American Forests and a host of local, national, and international sponsors will examine the interconnectedness of environmental, economic, and social elements in creating and maintaining healthy, sustainable cities.
For information on the study or the conference, contact American Forests at 202/955-4500 or www.amfor.org.
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