River planning includes ongoing activities and preparation of special studies. The following are examples:
Gravel removal study
A gravel removal study is being conducted in parts of the Snoqualmie River Basin. The purposes of the study are to characterize existing sediment accumulation and flooding conditions, and to evaluate the effectiveness of gravel removal for flood reduction in each of five specific study reaches in the Snoqualmie basin. These specific study reaches are the South Fork Snoqualmie River near North Bend, the lower Raging River through Fall City, the Raging River Delta and nearby mainstem Snoqualmie, the lower Tolt River, and the mainstem Snoqualmie near Carnation.
This evaluation of gravel removal is being done in response to community concerns that sediment accumulation causes flooding to worsen in these specific study areas. Historic responses to such sediment accumulation has included dredging (excavation across the full wetted channel) and gravel bar scalping (excavation only from the tops of gravel bars during the dry season). The study characterizes existing patterns and rates of sediment accumulation primarily by matching recent channel surveys to past surveys in the affected areas. Various gravel removal scenarios such as dredging or bar scalping are evaluated by hydraulic modeling. Alternatives to gravel removal, such as setting back existing levees, are also evaluated. Potential flood reduction is shown by comparison of existing conditions to dredged, bar-scalped, or levee setback scenarios. Anticipated impacts of all scenarios are described.
The listing of some salmonid species as threatened under the Endangered Species Act may affect the likelihood of using gravel removal for flood reduction, due to the impacts of gravel removal to salmonid habitat. The Snoqualmie River gravel removal study will be completed as intended, to address community concerns, and because the technical analyses of flooding, sediment deposition, and effects of various channel modifications will be useful for ongoing river management purposes regardless of whether such management includes gravel removal. Affected resource agencies, local jurisdictions, and tribes have been apprised of this study during its preparation. Beyond this study, the River and Floodplain Management Unit Section is committed to a channel monitoring program that assesses sediment transport and accumulation on a continued basis in selected reaches of the Snoqualmie River and parts of other major rivers in King County.
Forum and WRIA coordination
River and Floodplain Management Unit has a lead role in WRIA 10, White River Watershed planning and participates in King County's Watershed Forums and the WRIA groups. FHRS staff work closely with the Watershed Coordinators and their interjurisdictional partners on Forum and WRIA efforts including: prioritization of watershed projects related to flooding, fish, and water quality; implementation of restoration projects; participation in the WRIA technical groups; and preliminary planning for WRIA conservation plans.
Flood hazard education
Flood hazard education efforts aim to educate the public about the risks of living in flood-prone areas, steps they should take to reduce flooding, and programs available to help them insure properties against flood losses.
Complaint response and enforcement
Staff investigates complaints about flooding, channel migration, severe bank erosion and logjams on a year round basis, and especially during and immediately following flood events. During large floods, two-person teams patrol flooded areas along the major rivers to provide rapid response to flooding complaints and evaluate whether logjams pose an imminent threat to public safety and/or public facilities. Patrols also inspect County river facilities for structural damage and other warning signs that indicate potential facility failure that could adversely impact developed property and off channel habitat.
Violations of King County sensitive areas regulations, including floodplain regulations, are referred to DDES and/or other appropriate agencies for enforcement. Urban drainage complaints such as water quality problems and toxic waste dumping in unincorporated King County are referred to the WLR Division Drainage Services Section for investigation of potential violations of water quality codes. Other localized drainage and/or flooding complaints are referred to WLR Division's Drainage Services Section for investigation. Water quality complaints found in Cities are referred to the King County Trouble Call Coordinator, who will contact appropriate officials to initiate resolution of the problem. Large spills of toxic chemicals or petroleum products are referred to the Washington Department of Ecology. Fish kills are referred to the Washington Department of Fish and Wildlife.
Staff of the River and Floodplain Management Unit coordinate extensively with other King County agencies as well as numerous outside federal, state, local and tribal agencies on matters pertaining to floodplain management, flood control, and riverine and riparian habitat. The major coordination topics include:
Dam Operations: Participation in tabletop exercises related to Dam safety, flood control, and fish habitat.
Flood hazard reduction policy and regulatory consistency with the State Department of Ecology and DDES countywide; Snohomish County, the Cities of Duvall, Carnation, Snoqualmie and North Bend, and the Tulalip Tribes in the Snoqualmie basin; the City of Renton and the Muckleshoot Indian Tribe (MIT) in the Cedar River basin; the Cities of Auburn, Kent, Renton and Tukwila and MIT in the Green/Duwamish basin; and Pierce County and the Cities of Auburn and Pacific, MIT and the Puyallup Indian Tribe in the White River basin.
WRIA coordination with federal and state natural resource agencies, Counties, Cities, tribes and citizen groups in the Snohomish, Cedar/Sammamish, Green/Duwamish and White River basins. Major areas of coordination are habitat restoration projects and flooding impacts on riverine and riparian habitats.
Technical assistance to DDES and federal, state and local agencies regarding public and private development projects affecting floodplains; as well as input and review of bank stabilization and vegetation management guidelines prepared by other agencies, including the Army Corps of Engineers, the U.S. Natural Resources Conservation Service, and the State Departments of Ecology and Fish and Wildlife.
FEMA and the State regarding floodplain land acquisitions, home buyouts and elevations, property owners request and applications for letters of Map Amendment and Revision, and the federal flood insurance program.
Fish habitat utilization research conducted by U.S. Fish and Wildlife Service at bank stabilization sites in King County.
For questions about River Planning, please contact Sylvia Aro, Program Manager, River and Floodplain Management Section.