Seattle’s New (Age Old) Approach to Dealing With Stormwater Management

Within the City of Seattle, most land is fully developed, surrounded by hills adjoining large bodies of water. This makes it especially important to carefully manage rainwater to reduce environmental impacts. Because of its size and relationship to Longfellow Creek, the redevelopment of High Point in West Seattle offered Seattle Public Utilities (SPU) a unique opportunity to implement the largest natural drainage project in the city. Since the inception of SPU’s natural drainage program with the SEA Streets project in 2000, SPU has installed four natural drainage systems, including High Point, and has been nationally recognized for leadership in this area.

Natural drainage has become a standard tool for managing stormwater in Seattle, reducing flooding and improving environmental stewardship. Natural drainage systems strive to meet many goals: slow the flow of stormwater, allow the water to soak into the ground, filter and reduce pollution using the natural processes of soil and plants, reduce impervious (hard) surfaces, increase greenery, and make neighborhoods better places to walk and play.

The natural drainage system at High Point mimics nature in many ways, by using features such as swales to capture and naturally filter rainwater, and open, landscaped ponds or small wetland ponds to hold overflow. The end results are nothing short of remarkable. As Peg Staeheli, principal of SvR Design, one of the firms that assisted in the design of the High Point system, noted, “When we’re done, High Point will process water in a manner similar to a forest meadow.” High Point is an exemplary model for other large-scale developments, both locally and across the country. And SPU will continue to look for even more innovative ways to promote and encourage responsible stewardship of the environment here at home and beyond.

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Everything's "Swale" in the Neighborhood

As you begin your tour of High Point, one of its most innovative "attractions" is its 34-block natural drainage system, the largest of its kind in the U.S. The system protects the Longfellow Creek Watershed - 10 percent of which is represented by the High Point neighborhood. Because it is Seattle's most productive salmon-spawning stream, planners went to great lengths to ensure the neighborhood would have the least amount of impact on it. Enter the concept of natural drainage.

Standard residential streets are a major source of pollution. Traditionally storm water is channeled into gutters. Water then passes into pipes, then bigger pipes, picking up oil, fertilizer and pesticide run-off and other pollutants along the way before it empties directly into a creek, lake or pond. At High Point, a new system, much more in line with "Mother Nature's" approach to dealing with rain, was put in place.

As you walk through the neighborhood you'll notice that the streets tilt slightly toward one side and in place of gutters, shallow swales have been planted with a variety of native drought-tolerant shrubs, trees and grasses. The soil in the swales has been enriched with about 3 feet of compost much like the ground surface of a forest. The plants, soil and microorganisms function as a natural filter for toxins. Water from roofs, parking and streets is diverted to these swales, which, through natural processes, filter toxins from the water. By the time it reaches Longfellow Creek, the water has been naturally cleaned and matches the temperature of the creek's water so as not to compromise its inhabitants.

Concrete Facts About High Point

On 32nd Ave. SW, between Juneau and SW Raymond Streets, you'll find Washington's first porous concrete city street. A mixture of Portland cement, gravel and water, it has a rice cake look to it, with small gaps to capture rainwater, allowing water to seep into the soil beneath. Sidewalks next to the swales in many parts of High Point are also porous concrete. The porous pavement on the street and sidewalks captures the rainfall, allowing it to percolate into the ground where the soil cleans the polluted water naturally. The pavement also benefits plants and trees by allowing air and water to reach their root structures.

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