Greening Chicago’s Alleys

With about 3057 km (1900 mi) of alleys in the Windy City, the Chicago Department of Transportation (CDOT) is casting a green eye on the expansive maze of concrete alleyways.

Originally the alleys were designed on a grade, so water would flow out into the streets and into catch basins. Over the years, the graded designs in the alleys have worn down, and water that would otherwise flow out into the streets now collects and pools in the alleys, eventually making its way into residences. While CDOT considered building infrastructure in the alleys to handle the stormwater, the high price tag quickly ruled this option out. CDOT estimated it would cost about $100,000 per block to construct alleyway sewers.

In an effort to curb stormwater runoff that can lead to flooding in homes and overburden sewers, CDOT has implemented the Green Alley Program. The program entails replacing the alleys’ traditional concrete, asphalt, and pavers with permeable materials, which allow rainwater to seep into an alley’s surface. The permeable surfaces also reflect rather than retain heat to cool the immediate air in summer. The alleys of Chicago will be reconstructed with three permeable pavements — asphalt, concrete, and pavers. All have an infiltration rate that that allows water from heavier rainfalls to permeate through the pavement and sink into the ground. http://www.wef.org/ScienceTechnologyResources/Publications/WEFHighlights/2008Highlights/08May/May08Features.htm 

Water Environment Federation Highlights, May 2008