Editorial Letter: Grey Meets Green

Sept. 16, 2015

Citizens of Chicago, where I live, recently received some exciting news: Another element of our Deep Tunnel project is finally finished.

Construction on the Deep Tunnel system started in 1972 and is projected to be completed in 2029. Its most recent addition is the Thornton Reservoir, which can hold up to 7.9 billion gal of water. The reservoir is part of a system comprising 109 miles of tunnels and two other reservoirs (one yet to be constructed) that altogether will accommodate 20.55 billion gal of storm water and sewage in an effort to reduce flooding and combined sewer overflows.

The system is a typical grey infrastructure solution, which cities have been using for decades and continue to use. It’s important to note, however, that green infrastructure can be a great complement to existing grey infrastructure.

Green infrastructure imitates the natural hydrological process by absorbing storm water. It can make grey infrastructure more cost-efficient; for example, a bioswale can direct runoff to landscaped areas that retain and infiltrate rainwater, thus reducing the runoff that ends up in sewers and treatment plants. Green infrastructure also can enhance communities aesthetically and raise property values by upping the green space in the area.

In this issue, you will find a number of articles that show how green solutions can be a part of an engineer’s or utility’s toolbox. From living walls that stabilize slopes in Wisconsin (page 10), BMPs that capture storm water from a South Carolina stadium’s tailgating area (page 22), underground chambers that store runoff in Michigan (page 30) and a biocell system that works with trees and soil to process storm water in New York City (page 34), there are a variety of ways projects around the country are using green technologies to retrofit existing construction and enhance new designs. 

As regulations become more stringent, budgets continue to tighten and having clean water—and enough of it—becomes a more pressing concern in this country and around the world, a combination of grey and green infrastructure can help utilities and municipalities meet a multitude of goals. Grey infrastructure remains critical for adequate collection, conveyance and treatment of sewage and storm water, but green solutions make cities more sustainable and ease the pressure on aging infrastructure, and can help us create the sustainable and resilient cities of the future.

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