Chicago Green Alley Handbook

The Chicago Department of Transportation (CDOT) authored the Green Alley Handbook to encourage the use of best management practices (BMPs) in and around Chicago alleyways and to address impacts to the city’s infrastructure likely to result from projected increases in precipitation and temperature. The handbook promotes sustainable alley design and adjacent landscaping practices to help reduce flooding and manage stormwater, reduce urban heat, promote recycling, and conserve energy.  

Chicago alleyways were traditionally paved in impermeable asphalt or concrete and are not typically connected to the combined sewer system, resulting in frequent alleyway flooding. Climate change projections predict that winter and spring precipitation will increase 10% by the middle of the next century and by 20-30% by the end of the next century relative to current seasonal levels. Projected increases in precipitation caused by climate change will exacerbate problems with flooding and stormwater management. The city estimates that green alley design could return up to 80% of rainwater back into the ground, reducing localized flooding, reducing the load on the city’s stormwater system, and saving taxpayer money on stormwater infrastructure. The handbook promotes design features such as permeable pavements that can manage this stormwater and greatly reduce flooding.

Average annual temperature in Chicago is expected to increase by 1-1.5° F over the next few decades, and the number of very hot days (over 90° F) and extremely hot days (100° F) are expected to increase as well. The handbook addresses heat reduction by recommending building green roofs and green garage roofs atop buildings adjacent to alleyways to both manage stormwater and to reduce temperatures, and using high albedo (light solar-reflective) pavement to further reduce temperatures. New metal halide alley light fixtures are designed to conserve energy while reducing light pollution.

The guide contains four examples illustrating different combinations of BMPs. These applications contain a mix of conventional practices and more green practices, the balance depending on local site conditions. For example, although permeable pavements are preferable to impermeable surfaces, permeable pavements may not be a feasible design solution in every instance. In such an instance, the handbook suggests grading and pitching the impervious surface to a central infiltration trench that returns rainwater into the ground.

The handbook also suggests BMPs for property owners adjacent to alleys to install. These BMPs can supplement CDOT’s alley improvements by further reducing urban heat and preventing additional stormwater from flooding alleyways. Suggested BMPs include: recycling; composting; planting trees; landscaping with native plants; collecting rainwater in rain gardens or rain barrels or cisterns; and using permeable pavements, green roofs, and vegetated swales. The handbook contains a FAQ and list of publications as a resource for property owners.

The handbook was developed as part of the Chicago Green Alley Program, which began as a pilot in 2006 to help make Chicago's 1,900 miles (approx. 3,500 acres) of public alleys more sustainable and more capable of accommodating projected increases in precipitation and temperature associated with climate change. As of 2012, over 175 green alleys have been installed in Chicago since the program's inception in 2006. Chicago green infrastructure, which includes green alleys, has helped divert over 70 million gallons of stormwater in 2009 from the combined sewer overflow system. Data from the Chicago Green Alley program has shown green infrastructure technologies to be an estimated 3 to 6 times more effective in managing stormwater per $1,000 invested than conventional methods.

 

This Adaptation Clearinghouse entry was prepared with support from the Federal Highway Administration. This entry was last updated on February 5, 2015.

 

Publication Date: 2010

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