Forty-two percent of the surface area in St. Paul is impervious. What happens to the rain water that hits those surfaces? What can be done to reduce the amount of run-off and increase the quality of water in urban areas? On March 14 about 25 people spent two and a half hours at the South St. Anthony Rec Center considering such questions. The event was one of a series of roundtable discussions sponsored by Eureka Recycling.
Ron Struss, a University of Minnesota Extension educator, told the group that in undevel-oped areas only about 10 percent of rainwater runs off the earth, while in urban areas that amount can approach 50 percent.
In cities, run-off must be diverted to storm sewers, and it picks up various kinds of pollution on its way to the lakes and rivers where it ends up.
Struss called this nonpoint-source pollution “a thousand points of blight” and said that the challenge facing St. Paul and other urban areas is how to increase infiltration, thus recharging the ground water supply and reducing pollution.
He mentioned three strategies for increasing infiltration: rain gardens, porous pavement and green roofs.
Rain gardens consist of depressions with special plantings that can tolerate perpetually moist conditions. Storm run-off is diverted from street gutters, often via curb-cuts, to a rain garden, where it soaks into the earth instead of going into the sewer system.
In St. Paul, said Struss, the best chance for creating rain gardens is when streets are repaved and curbs and gutters are replaced. That opportunity is being seized in the Como Park neighborhood this spring and summer, when the city will create several large rain gardens and encourage residents to add smaller ones to boulevards.
According to Struss, rain gardens capture up to 85 percent of run-off.
He said that some cities have experimented with various kinds of porous surfaces as alternatives to concrete sidewalks.
Another way to reduce run-off, Struss said, is with “green roofs,” where shingles or tar are replaced with plantings that absorb some of the rainwater.