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American Society of Landscape Architects


October 2007 Issue

Seattle’s Green Pipes
A city known for its rain installs natural stormwater drainage systems.

By Lisa Owens Viani

Seattle's Greem Pipes Seattle Public Utilities

As part of a citywide effort to restore the water bodies that surround it—Puget Sound, Lake Washington, Lake Union, and innumerable creeks and rivers—Seattle is softening its ecological footprint, ripping out pavement to mimic the forest floor that once covered the land and replacing concrete gutters and ditches with vegetated swales and rain gardens. Between 1972 and 1996, as the city grew and urbanized, its canopy cover shrank to 13 percent, while stormwater runoff increased by 7.5 million cubic feet. Dismayed by the associated water-quality impacts, the city’s Department of Transportation and Public Utilities Department began working together to implement a series of deceptively unassuming stormwater projects they christened “natural drainage systems” (NDS). The first natural drainage project—known as SEA Street (SEA for “street edge alternative”)—was put in the ground in 2000 as a pilot. It has been so successful in intercepting and slowing urban runoff—reducing flows from the two-year storm by 99 percent—that several subsequent projects, each increasing in scale, have followed, and many more are in the planning stages.

The idea for SEA Street was spawned by Seattle’s late-1990s mayor, Paul Schell, who allocated millions of dollars toward in-the-ground environmental restoration projects. While many of the projects were stream restoration projects, “we felt that we were kind of mitigating after the fact and asked ourselves what we could do as a pilot to reduce our footprint before the runoff got to the creek,” explains Darla Inglis, Seattle Public Utilities’ strategic adviser on water quality. “We decided that we wanted to redesign a street to reduce runoff volume that would damage a creek.” The success of SEA Street, both in performance and community engagement, says Inglis, was beyond expectations and led to expanded interest in doing more with this model.

A mayor’s green vision aside, what else is motivating the city to pull up pipes and curve its streets? “Salmon,” reply Shane DeWald, ASLA, senior landscape architect with the Department of Transportation, and Bob Spencer, the city’s creek steward, in unison. Stormwater—and the sediment, grease, oil, pesticides, and other urban pollutants it contains—is bad news for the chinook and coho salmon and steelhead trout that live in Puget Sound and breed in its watersheds. These are listed as “endangered,” which entitles them to protection under the Endangered Species Act. Puget Sound is also habitat for orcas, which were recently added to the federal endangered species list, and the current governor of Washington, Christine Gregoire, has directed a huge amount of attention and resources toward improving the sound’s water quality.

But concern for fish (and whales) is only one driver of the natural drainage projects. Despite the clout of federally listed species, Seattle’s NDS projects are driven less by legislation than the city’s attempt to improve the “physical, chemical, and biological aspects” of water quality in a more holistic, watershed-based approach, says Christopher May, the city’s stormwater and urban stream habitat lead. In 2004, the current mayor, Greg Nickles, added to Schell’s earlier efforts in a new initiative called “Restore Our Waters.” As part of that initiative, he directed all city departments to examine their impact on water resources. Explains Gary Schimek, manager of the Public Utilities’ Urban Watersheds Group, “The whole idea is to improve water quality in receiving water bodies, to improve flow regimens in creeks, and also to deal with capacity issues in our pipe systems. We’re working with folks in other departments in the city to make development projects as green as possible; if there’s a street improvement project, we try to make it low impact.”

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