There's something particularly Worldchanging about the inventive concept of green urban alleyways, which replaces the typically disregarded back alley with walkways, recreation spaces and even ecosystems. Here's a closer look at green alley initiatives in Chicago, where a City-led initiative has determined that greening alleyways is not just a feel-good action, but a worthy civic improvement.

Conventional alley systems in major cities present a handful of sustainability problems. In Chicago, home to over 1900 miles of back alleys — the concrete equivalent of five major airports, and the largest such system in the world — the sheer acreage of alleyways significantly exacerbates stormwater damage, watershed pollution and urban heat island effects. Runoff from heavy storms occasionally overtaxes Chicago’s combined sewer system, flooding basements and streets. In some instances, the runoff load exceeds the capacity of sewage treatment facilities, flushing polluted water directly into Lake Michigan.

In 2006, the City of Chicago’s Department of Transportation instituted a program to reduce damage wreaked by alleyways. Conventional concrete and asphalt are gradually being replaced by a variety of permeable pavers, some made from recycled industrial wastes like slag and tire rubber. The new porous paving allows up to 80 percent of rainwater to infiltrate the subsoil, filtering out pollutants as water returns to the aquifer and, ultimately, the lake. Chicago removes about one billion gallons of water from Lake Michigan each year and less than 1 percent of that returns to the watershed. The new resurfaced green alleys reclaim industrial waste, alleviate water damage and pollution and reduce urban interference with the natural water cycle. In addition, all new pavers are high-albedo — or light-reflective — to reduce urban heat-island effects. Energy-efficient, dark-sky-compliant light fixtures are also included in each alley makeover.

As you can see in the before and after photos at left, most of Chicago's updated alleys don't look dramatically different. They're still providing the storage, inter-building access and transport space they always have -- they just perform better, which makes them tidier and more inviting.

And the cost to the taxpayer? Surprisingly, building alleys that are efficient, environmentally beneficial and safe doesn't cost much beyond what we're already spending to build the lesser kind. Permeable concrete costs about $45 per cubic yard — comparable to the price of conventional pavers. The program has been well received and all of Chicago's alleys slated for renewal will get the green treatment.

More than 80 of Chicago’s alleys have been resurfaced in the past two years. The Department of Transportation even created a Green Alley Handbook, providing diagrams of various alley makeovers to suit different site conditions, along with guidelines for how homeowners can help reduce stormwater runoff by planting rain gardens, installing bioswales, rain cisterns and green roofs. We're happy to see that these spaces, once largely ignored, are being recognized for their impact on the built environment.

Sharon Hoyer is a freelance writer covering sustainability, culture and arts in Chicago. You can find more of her writings on the environment at Centerstage Chicago. You can find her in the garden or on her bike.

Photo source: Chicago Green Alley Handbook