Whispering Firs is a regional stormwater facility that treats stormwater from Silverdale, WA, a community located on the Kitsap Peninsula in the State of Washington.
Built on a site that was a former trailer park, Silverdale’s first stormwater park manages runoff from over 115 acres of development from the Ridgetop neighborhood that previously flowed untreated to Clear Creek. The park is part of an ongoing effort to bring Clear Creek back to a functional stream ecosystem after being damaged from farming and development. The goals are to reduce flooding for the people in Silverdale, work on the stream’s ecosystem, and clean the water so when it’s sent to the Dyes Inlet, it’s safe for salmon, orcas, and people. The project also provides a peaceful destination for walking, picnicking, and discovering nature.
Stormwater is first directed to a Vortechs hydrodynamic separator for pretreatment, removing trash, sediment, and debris. Stormwater is then directed to four Filterra Bioscape cells. Filterra is similar to bioretention but has been optimized for high volume/flow treatment and high pollutant removal. Filterra media captures pollutants such as TSS, phosphorus, nitrogen, copper, and zinc. The Filterra Media allows for a reduction in footprint of up to 95% versus traditional bioretention practices, making it the perfect LID solution for high volume Stormwater treatment. The Filterra cells were planted with native plants to resemble a natural wetland.
Whispering Firs is the second stormwater park in Kitsap County, the first being in Manchester, which also uses Filterra. The project received the Innovative Stormwater Project Award from the Pacific Northwest Clean Water Association (PNCWA) and a 2019 Top Project Award from Stormwater Solutions Magazine.