Hylebos Watershed Spring 2003

Introduction | Locations | Land Use | Methods | Results & Discussion | Conclusion | Work Cited
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History

Hylebos Watershed History

Historically, the 18 sq. mile (46.6 km2) Hylebos watershed was a small but productive salmonid bearing watershed. Prior to development, the Hylebos watershed supported fairly substantial runs of Coho, Chinook, and Chum Salmon, and residential populations of Cutthroat Trout. However, only small runs of salmonids presently use a small area of this watershed (Friends of Hylebos 2001). The decrease in salmonid runs within the Hylebos watershed is indicative of the extensive development that has occurred within most of this small watershed. Most of the forest and wetlands that the once covered the watershed have been replaced with commercial, industrial, residential, and agricultural (primarily pasture land) developments. A large portion of the watersheds primary waterways have been channelized and culverted. As the land within the watershed and bordering its main waterways was developed, the amount of impervious surfaces was dramatically increased. This has caused significant increases in peak flows and decreased base flows. The increased peak flows degrade the aquatic habitat within the watershed by causing extensive erosion, increased turbidity, and blowout of salmonid reds. In addition to increased peak flows, prevention of precipitation to infiltrate the surface prevents the supply of adequate base flows to sustain the aquatic habitats in between precipitation events.

Hylebos Creek begins in Federal Way, near the SeaTac Mall, and flows through the cities of Federal Way, Fife, Milton, Edgewood, and Tacoma, the Puyallup Reservation and parts of unincorporated King and Pierce Counties. Its three main tributaries flow south along Interstate 5 and Highway 99 into the Hylebos Waterway and Commencement Bay. The Hylebos basin drains 18 square miles from Federal Way to Commencement Bay and encompasses 35 stream miles, 250 acres of wetlands, 11 named lakes and numerous unnamed lakes (http://www.hylebos.org). As the Hylebos makes it way downstream, it meanders through residential, industrial, commercial and agricultural development before finally entering into the Commencement Bay.

Unfortunately due to an increase in population and urban development, the Hylebos Watershed has transformed into paved over wetlands, re-routed salmon spawning stream channels, and deforestation. Currently, asphalt and other impervious surfaces are quickly replacing the watershed's natural drainage functions and salmon spawning areas. Human actions impact salmon life by the following: decrease in available spawning areas, loss of protective wetlands, devasting floods, decrease in salmon eggs, bank erosion, and an increase in stream temperature. As a result, surface runoff from roads and neighboring farmland are increasing the level of pollutants that deposit into the stream.

On the bright side, in 1991, King County implemented a basin plan that described actions to control flooding and restore salmon spawning areas. Since then King County and the City of Federal Way have embarked on several restoration and conservation projects in the Hylebos Creek Watershed. The City of Federal Way has invested over $15 million, alone, toward the construction of storm water detention ponds (http://www.hylebos.org). Detention ponds are artificial structures, built down stream from impervious surfaces to slow and retain storm water and allow sediment to settle before releasing back into the stream. The detention ponds, located in the Hylebos Creek Watershed, are used to decrease the amount of flooding problems and improve the quality of water. For further historical stream flow data visit, http://waterdata.usgs.gov/nwis/inventory/?site_no=12103020

Introduction | Locations | Land Use | Methods | Results & Discussion | Conclusion | Work Cited
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