Flooding in the White River Watershed

The White River begins at the Emmons and Winthrop glaciers on Mount Rainier. The White River is joined by the Greenwater River and flows between the cities of Enumclaw and Buckley, then through the Muckleshoot Indian Reservation and the cities of Auburn, Algona, and Pacific. The White River continues south through the City of Sumner before joining the Puyallup River. 

Flood risks in the watershed

• Most major White River floods occur from November through February.
• The lower White River landscape is relatively flat, so flooding can spread quickly across a large area.
• Scientific models show flood risks along the lower White River are likely to increase over time because of ongoing sediment deposition. When sediment is deposited in the river channel and floodplain, it makes the river channel shallower, and therefore more likely to flood.
• The cities of Pacific, Sumner, and Auburn have experienced flooding impacts from channel sedimentation.
• Pacific also experiences more frequent stormwater flooding due to the buildup of sediment in the river. Sediment buildup can cause higher river levels to back up into the city’s stormwater system.  

Flood infrastructure in the watershed

King County coordinates with the U.S. Army Corps of Engineers that owns and operates the Mud Mountain Dam. Although it is not possible to prevent all flooding, the Dam is an important part of flood risk reduction in the watershed.

<Insert photo of Mud Mountain Dam>

The levees and revetments maintained by King County along the White River address temporary flooding on land, bank erosion, and channel migration risks. A levee is a raised structure built along a riverbank to contain, control, or divert the flow of water. A revetment is a structure built along a riverbank to reduce erosion risks.

Levees and revetments are primarily located along the lower White River in King County. The Greenwater River has two revetments. The Countyline levee maintained by King County extends into Pierce County.

The importance of healthy floodplains

Connected floodplains provide space for flood water storage and habitat for fish and wildlife. The White River watershed is home to the last remaining population of spring-run Chinook in the south Puget Sound. Changing the natural or built environment can affect fish habitat, including water quality and temperature. We consider potential impacts to these species when designing flood risk reduction projects. Learn more about salmon in the watershed by visiting the WRIA 10 Salmon Habitat Protection and Restoration Strategy.