Stormwater management technology helps protect, improve WA watersheds

New stormwater management tools are being integrated in cities and communities across Western Washington state to protect watersheds.

Jun 21st, 2013
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SAN FRANCISCO, CA, June 21, 2013 -- New stormwater management tools are being implemented in cities and communities throughout Western Washington looking for an effective solution for keeping their watersheds healthy. The area of the state has been a longtime practitioner in low-impact development approaches for stormwater management.

The Silva Cell, developed by DeepRoot, is an underground frame that allows large trees to have soil access so they can grow healthily in a small urban space even if surrounded by concrete. The Washington State Department of Ecology found, through extensive modeling, that a Silva Cell system can have as much impact as a bioretention facility.

"Cities want to surround residents with trees. It improves communities and manages stormwater flow," stated Graham Ray, CEO of DeepRoot. "Many Silva Cells are installed in the Seattle metro area and in Renton and Tacoma, but now that we are certified by one of the nation's most influential state agencies, we hope people will realize just how effective a tool this is for absorbing water from ordinary storms -- even in places where it rains every day."

Western Washington has a regional consensus to protect the purity and clarity of Puget Sound. The state has therefore developed some of the highest standards and requirements for any product or project to be designated as a "stormwater management solution." Silva Cell's designation by the state validates DeepRoot's efforts. The approval also means that contractors can use the Silva Cell on project sites without seeking any additional approval.

The State of Washington has made it easy for municipal planners and urban designers to utilize Silva Cells. In conjunction with local engineering firm HDR, DeepRoot developed a step-by-step design manual for using Silva Cells for maximum bioretention and for maximum impact on the watershed in which trees are installed.

"Because Silva Cells are a structural support system and the soil within the cells can be built to bioretention soil standards, it was clear to us at Ecology that it should be considered equivalent," said Doug Howie of the Washington State Department of Ecology. "Previously, Silva Cells were approved as functionally equivalent to a raingarden; the new designation that Silva Cells are functionally equivalent to bioretention is an important distinction that allows Silva Cells to be used in many more stormwater applications."

The modeling by the state's Department of Ecology found that Silva Cells allow for bioretention of water by supporting the growth of large, healthy trees. They also offer additional flow control benefits by capturing water with their canopies, evaporations from tree leaves, and enhanced infiltration using bioretention soils.

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