More than half of the rainwater that falls on a typical city block will leave as runoff.
More than half of the rainwater that falls on a typical city block, one with 75% or more impervious cover — such as roads or parking lots — will leave as runoff, according to the Environmental Protection Agency. This runoff includes metals, oils, fertilizers and other particulate matter, the Connecticut researchers note. Easy-to-construct rain gardens — shallow depressions in the earth landscaped with hardy shrubs and plants such as chokeberry or winterberry surrounded by bark mulch — offer a simple remedy to this problem, they say.
Properly designed “rain gardens” can effectively trap and retain up to 99 percent of common pollutants in urban storm runoff, potentially improving water quality and promoting the conversion of some pollutants into less harmful compounds, according to new research scheduled for publication in the Feb. 15 issue of the American Chemical Society journal, Environmental Science and Technology. The affordable, easy-to-design gardens could help solve one of the nation’s most pressing pollution problems. (2006) ScienceDaily via American Chemical Society.
http://www.sciencedaily.com/releases/2006/01/060126193136.htm