Green Cities, Great Lakes: Using Green Infrastructure to Reduce Combined Sewer Overflows, Ecojustice

Beneath our urban centres are hundreds of kilometres of pipes that transport sewage and stormwater runoff – many originally built in the early twentieth century. These systems were often designed to accommodate both stormwater and municipal sewage in a single pipe referred to as a combined sewer.

Increased urbanization has reduced the natural services provided by green spaces (absorb, filter and slow water runoff).These natural systems can be used in urban designa and planning, commonly called “green infrastructure.” Green infrastructure refers to both natural corridors like parks and wetlands, as well as engineered, human-designed systems that mimic nature, such as green roofs or bioswales.

Green infrastructure manages stormwater at the source by capturing runoff and retaining it before it can reach the sewer system. Using green infrastructure in tandem with, or in-place of, hard (grey) infrastructure solutions, such as pipes and storage tunnels, reduces stormwater runoff volumes. This in turn reduces CSOs and mitigates the amount of pollution entering local waters, and extends the life of the exisiting grey infrastructire.


Using Green Infrastructure to Reduce Combined Sewer Overflows

August 2008

By Liat Podolsky (Science Researcher, Ecojustice) and Dr. Elaine MacDonald

(Senior Staff Scientist, Ecojustice) with invaluable assistance

from Jode Roberts, Judah Harrison and Anastasia Lintner