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MIT Better World

On the roof: Judith Layzer with sedums, drought-tolerant plants, which insulate the house below, keeping it cool in summer and warm in winter.


By Leda Zimmerman

“I hate waste.” As a social scientist who helps cities craft smart policies for reducing environmental impacts, Layzer sees a lot of squandering, but one area that has recently earned her particular scrutiny is stormwater runoff.

What was once an obscure matter for municipal managers is swiftly becoming an urgent, national environmental challenge: the EPA estimates that 10 trillion gallons of untreated rainwater and melted snow pour off roofs, roads, parking lots, and other impervious surfaces each year, overwhelming sewer systems, infiltrating rivers and waterways, threatening drinking water supplies, and degrading ecosystems.

This “gray” infrastructure depends on steel-colored networks of cement and metal pipes, valves, pumps, and energy-hungry treatment plants. As urban development escalates, and climate change brings rising seas and monster storms, current water management systems are failing, says Layzer. Their repair and replacement is increasingly expensive in a global economy where there is stiff competition for building materials.
Cities desperately need an alternative to infrastructure that pollutes an ocean’s worth of precious fresh water annually, then dumps it at enormous cost.

The answer, Layzer believes, is green stormwater infrastructure. This comprehensive approach emulates nature by directing stormwater into soil and other permeable surfaces, where it can first nourish trees and plants, and then percolate downward. Stormwater becomes purified on its way to underground aquifers or rivers and lakes, protecting watersheds and ecosystems. Even better, says Layzer, “It is a solution that not only solves the problem, but gives you extra benefits.” That’s because this method of stormwater remediation “has the advantage of using much less energy, creating new habitats, and improving public health by cleaning the air and mitigating the heat island effect,” Layzer says.

As director of a national Urban Sustainability Assessment Project, Layzer is developing a methodology to help busy city managers identify the best and most cost-effective environmental practices. She is convinced that green stormwater infrastructure can deliver on all fronts. She points to Philadelphia, which may be the poster child for gray-to-green infrastructure conversion. To meet Clean Water Act requirements, the city has agreed to a 25-year transformation of gray infrastructure into “greened acres,” diverting up to 90 percent of annual rainfall from these areas to green roofs, porous paving, rain gardens, and bioswales, gentle slopes that use vegetation and compost to filter silt and pollution from surface runoff water. The city estimates its green investment will save billions over maintaining its old, gray system.

With MIT graduate students, Layzer is undertaking a green storm-water infrastructure assessment that explores the experience of Philadelphia and other U.S. cities. This work will be posted online as an open source tool for city planners, and then incorporated into a book Layzer says will “reconceptualize cities as parts of ecological systems rather than simply as built environments.” The bottom line, Layzer hopes to demonstrate, is that gray solutions are financially and ecologically unsustainable. They are also “wasteful, unbeautiful, and inelegant” when compared to “the miraculous system that nature came up with for cleaning the water and the air and creating a healthy habitat.”