Using green and gray infrastructure to manage stormwater

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Waterfront Toronto

Sherbourne Common is the first park in Canada to integrate a sto… Read More Sherbourne Common is the first park in Canada to integrate a stormwater treatment facility into its design. Runoff is disinfected in the pavilion’s basement using ultraviolet light.

Waterfront Toronto

Designed by artist Jill Anholt, Sherbourne Common’s “Light S… Read More Designed by artist Jill Anholt, Sherbourne Common’s “Light Showers” are actually part of the park’s stormwater treatment system.

Black & Veatch

Omaha’s oldest neighborhood is integrating traditional infrast… Read More Omaha’s oldest neighborhood is integrating traditional infrastructure with green streets, bioswales, and a regional detention basin. Improvements to 108-acre Fontenelle Park include recreational opportunities.

Same goal, two approaches

As communities with combined sewer overflow (CSO) problems and/or compliance decrees began evaluating their programs, officials and planners realized that “green” infrastructure could be used to offset capital-intensive “gray” infrastructure like sewer separation, storage tanks, tunnels, and treatment facilities. The typical green strategy is to use source-control technologies to offset millions in new gray infrastructure costs by reducing inflow into the collection system.

There are other benefits as well. Green streets, bio-retention cells, and rain gardens improve the aesthetics of the areas in which they’re located. Because areas with the worst CSOs are usually those with older infrastructure and lower socioeconomic conditions, green technologies also could be used to spark urban revitalization.

In short, green solutions offer something that gray solutions inherently can’t. They’re visible, desirable, and indicate a community that’s vibrant and progressive. So the “green wave” rolled into public works departments nationwide, nudging traditional solutions from the top of conversations.

Then something happened. As decentralized wastewater treatment, wetlands, and natural treatment systems garnered media coverage, and the overall value of green infrastructure to stormwater and sewer systems became more widely recognized, communities discovered that plans with only nature-inspired approaches aren’t necessarily more economically feasible or sustainable. Nor can they completely meet the significant water management needs or goals of urban areas.

The idea that highly impervious downtowns can easily “go green” is erroneous. Green roofs control runoff, cool urban heat islands, and lower air pollution, but few older buildings can support their weight without significant upgrades.

Similar obstacles apply to converting existing sidewalks and right-of-way into green streets. It’s extremely difficult to retrofit open space for planter boxes, curb cuts, and bioswales in developed downtown core areas.

Finally, whether they realize it or not, residents support green solutions only up to a point. Given the choice, few would manage their own waste with personal treatment wetlands or composting toilets. Public health advances and economies of scale carried civilization toward centralized waste management, and efficient water resource recovery favors communal over individual effort.

Thus, when it comes to size, scale, and process efficiency, green solutions can rarely compete with tried-and-true collection and treatment processes. Instead of distinguishing them by color, let’s view each as an approach that offers a means to an end: a cleaner environment and better quality of life.

Next page: An integrated solution