In Seattle, When It Rains, It Drains-Naturally: Learn How SEA Street Convinced the City to Use Natural Drainage as the Principal Approach to Managing Storm Water in Areas That Drain Directly into Creeks and Why Other Communities Can Do the Same
Edwards, Amy, The Public Manager
Why can other communities copy Seattle's Natural Drainage Systems (NDS) program? For one thing, this urban innovation can be created as part of street improvements or through new construction. It carries special advantages for areas of new development since installing it at the beginning leads to cost savings over time. Second, the technical components of NDS are easily understood and integrated into the planning of private developers as well as public agencies. Third, natural drainage systems generally cost 15 to 25 percent less than traditional street redevelopment, which requires curbs, gutters, catch basins, asphalt, and sidewalks.
These benefits and returns on investment haven't escaped the notice of other city and town governments. Nor have the actual results NDS has achieved in Seattle. Representatives of some fifty nearby communities and others across the United States and Canada have toured the project's sites. Program staff members have answered hundreds of e-mail inquiries from Washington State to Tasmania.
Challenges of Storm Water Management
What drives this broad interest is the variety of problems posed by storm water management to communities everywhere in the world. In many of them, handling the runoff from regular rainfall, occasional downpours, and sudden deluges is a normal challenge. In others, the monsoon cycle and hurricane or typhoon season are also normal but pose much tougher, more serious threats.
As in other cities, the rooftops, streets, and parking lots of Seattle do not allow rainwater to seep into the soil. And Seattle, like other cities, has long relied on arrangements of street gutters, underground pipes, tanks, and storm sewers to rid its urban areas of surplus rainwater by carrying it away from impervious surfaces and sending it to expensive treatment plants or dumping it in nearby natural bodies of water. In Seattle's case, that means creeks, lakes, and ultimately, Puget Sound--all features that give the city its unusual appeal.
One of the problems with traditional drainage systems is that they propel sporadic, often sudden, and fast-flowing storm runoff into these streams, rivers, lakes, and bays. The result is abnormal erosion and dropping of sediment, which harms the environment of aquatic species. Just as bad, runoff from storms carries manmade pollutants from landscaping, transportation, and business, as well as bacteria from animal waste. This further contaminates the natural habitats of freshwater fish and marine ecosystems and damages the food chain on which fish and other wildlife depend. Most traditional engineering solutions to these negative impacts are either excessively costly or don't work.
By contrast, Seattle's system does not just move and delay storm water, but reduces and treats it. It redesigns residential streets so they can handle most runoff naturally and cost-efficiently by staged absorption through the ground. The system increases soil and plants along street edges and links them together in vegetated swales and storm water cascades. Thus, Seattle's pilot project, Street Edge Alternatives (SEA Street), reduced impervious surface by 11 percent, added a hundred trees and 1,100 shrubs, and installed swales for water retention. Typical of NDS projects, it involved landscaping a 2.3-acre area to make it look more as it did before development and to restore the actions of nature that urban development had removed.
Natural drainage projects like this, which have been called "green infrastructure," increase rainwater seepage into natural underground systems. They change the flow of water into streams and cut the amounts of pollutant reaching aquatic ecosystems. Two years of monitoring showed that SEA Street reduced the total volume of storm water leaving the street by 98 percent.
SEA Street also serves other purposes. With its curvilinear design, bending smoothly and regularly but moving in a single overall direction, the street slows and calms traffic. …