Leary Stormwater Treatment Wetland

In the summer of 2008, the City constructed a new water quality facility in the form of a stormwater treatment wetland.

This facility collects stormwater from watershed 510, 17.6 acres of urban commercial development. This is the second of the City's downtown regional facilities to be constructed. The Leary Stormwater Treatment Wetland is a stormwater treatment facility designed to remove sediment and pollutants from stormwater flowing from City streets. When it rains, stormwater runoff flows from Leary Way, 159th Place, and Bear Creek Parkway into the pond. As the water slowly flows from one end of the pond to the other, sediment settles to the bottom. Biological processes also help to filter out oil and grease and metals from the stormwater so that cleaner water is released into the Sammamish River.

What is a Stormwater Treatment Wetland?

Stormwater treatment wetlands (a.k.a. constructed wetlands) are structural practices similar to wet ponds that incorporate wetland plants in a shallow pool. As stormwater runoff flows through the wetland, pollutant removal is achieved by settling and biological uptake within the practice. Wetlands are among the most effective stormwater practices in terms of pollutant removal, and also offer aesthetic value. While natural wetlands can sometimes be used to treat stormwater runoff that has been properly pretreated, stormwater wetlands are fundamentally different from natural wetland systems. Stormwater wetlands are designed specifically for the purpose of treating stormwater runoff, and typically have less biodiversity than natural wetlands both in terms of plant and animal life. There are several design variations of the stormwater wetland, each design differing in the relative amounts of shallow and deep water, and dry storage above the wetland. Since stormwater treatment wetlands must be maintained, they are not subject to environmental protection regulations typical of natural wetlands, but when they are not being maintained they provide similar habitat benefits.

Design Information

One of the first of its kind for Redmond, the Stormwater Treatment Wetland was selected because it would blend in well to the natural open space in the vicinity, and because Ecology has identified this as an approved treatment method for both “Basic” and “Enhanced” stormwater treatment. The Design of this project is documented in KPG’s Design Report and Drainage Areas; and, As-Built Drawing and As-Built Drawing Landscape Plans.