1/3 of a region's impermeable surface

"In densely urbanized areas, streets and sidewalks often constitute around 1/3 of a region's impermeable surface."

-- from "Using Individual Parcel Assessments to Improve Stormwater Management," by Meliss Keeley (in Spring 2007 Journal of the American Planning Association).

note: the Spring issue of JAPA has some very good articles on water issues, including the article cited above. We'll be running an article on stormwater management more geared to citizen planners in the Summer issue of the Planning Commissioners Journal.