The King County Flood Control District invests resources in the Snoqualmie/South Fork Skykomish River Basin to protect public safety, the regional economy, and critical infrastructure.
For the purposes of the Flood District’s budgeting and planning, the Snoqualmie/South Fork Skykomish River Basin includes the Lower Snoqualmie River, Raging River, Snoqualmie River, South Fork Skykomish River, Tolt River, and Upper Snoqualmie River.
Information about individual rivers in the basin are available below.
The Lower Snoqualmie River basin begins at Snoqualmie Falls and generally drains north toward Snohomish County. The river meanders in wide loops through a largely agricultural valley floodplain, passing through the unincorporated community of Fall City and the cities of Carnation and Duvall. Aside from these three residential and commercial centers, most of the lower Snoqualmie valley supports rural residential, agricultural, and recreational land uses.
The Snoqualmie River is prone to flooding and typically has annual multiple flood events that inundate local farmland and close low-lying roads. The City of Snoqualmie is one of the most flood prone cities in the United States. Flooding causes significant property, economic, and social losses to residents, businesses, and farms. Impacts include injuries to citizens, health hazards, economic and property damages, lost revenue, and increased demand on public safety and infrastructure-related services.
The Raging River flows into the Snoqualmie River from the southwest at Fall City, downstream of Snoqualmie Falls. The entire basin is located in unincorporated King County; the communities of Preston, near River Mile 5 at Interstate 90, and Fall City, at the mouth, are centers of residential and commercial land use. Timber harvesting has been the main land use in the upper two-thirds of the Raging River basin since the early 1900s. Residential development exists throughout the Raging River valley bottom.
In November 1990, record flows (6,220 cubic feet per second) overtopped the right bank along Preston-Fall City Road and nearly filled the entire opening under the Preston-Fall City Bridge in Fall City.
The S.F. Skykomish River basin includes Beckler River and Miller River which join the Skykomish River. Formed at the confluence of the Tye and Foss Rivers about 13 river miles upstream of the King and Snohomish county line, the S.F. Skykomish River is a relatively unpolluted and free-flowing river, with no significant dams in the watershed. It includes several waterfalls and feeds the Snohomish River which empties into Puget Sound at Port Gardner in Everett. The State of Washington has designated many portions of the South Fork Skykomish as scenic.
Homes and other structures at many locations along the South Fork Skykomish River have suffered damage from deep and fast moving water resulting from floods. The largest flood on record in Gold Bar (Skykomish County) occurred in November 1990, when South Fork Skykomish River flows reached 102,000 cubic feet per second. This flood also inundated the Town of Skykomish in King County. During significant flood events, homes in the Town of Skykomish have been struck by flood-borne debris moving at high speeds.
The Tolt River is a major tributary that enters the Snoqualmie River from the east, near the City of Carnation. Its headwaters are at the crest of the Cascades. Land use in the Tolt River valley is primarily residential with lower density development in the upstream valley and higher density development downstream. The upper reaches of the Tolt River basin are mostly within the Forest Production District, where timber harvesting has occurred on an ongoing basis since the early 1900s. The City of Seattle operates a water supply and hydroelectric power dam on the South Fork Tolt River, which was completed in 1963.
Most of the Tolt River basin is in unincorporated King County. The City of Carnation is located along the north bank of the river. Flood and erosion hazards affect unincorporated areas and incorporated areas. Levees line both banks from about River Mile 2 to the mouth. The State Route 203 Bridge crosses the Tolt River at River Mile 0.55 and the Snoqualmie Valley Trail Bridge, formerly a railroad bridge, crosses the Tolt River at River Mile 1.1.
Major floods on the Tolt River have occurred in 1990, 1995 and 1996, in some cases damaging levees and necessitating repairs.
The Snoqualmie River’s three forks (North Fork, Middle Fork and South Fork) begin in the high peaks of the Cascades, follow steep watercourses through the mountains to the confluence near the foot of Mount Si, and combine to form the mainstem Snoqualmie River. The river flows through the City of Snoqualmie and over Snoqualmie Falls.
Land uses along the Snoqualmie River in North Bend and Snoqualmie primarily consist of residential and commercial uses. Rural residential and forestry dominate the upper basin. Flows along the forks are unregulated, with no major reservoirs in the system. Several hydroelectric facilities divert flows, including a dam operated by Puget Sound Energy immediately above Snoqualmie Falls. All of the hydroelectric facilities in this sub-basin lack sufficient storage volumes to control downstream flooding.
The highest flows recorded at the Snoqualmie River were 78,800 cubic feet per second in November 1990. Floods in 1995 and 1996 caused damage to King County levees and revetments in this area. Most of this damage has been repaired.
Investments in the Basin
Capital Investment Strategy
A capital investment strategy (CIS) proposes a sequence of coordinated projects to address the most critical flood and erosion risks and to restore habitat along a specified stretch of river or within a river basin.
The strategy highlights near-term, medium-term, and long-term projects and actions that were identified during an assessment of key problem areas and potential solutions.
Capital investment strategies are directed by the Flood Control District, completed by King County, and eventually approved as policy guidance by the District’s Executive Committee.
Circle River Ranch (South Fork Snoqualmie) This project evaluates actions to reduce long term risks from channel migration in the Circle River Ranch Neighborhood on the South Fork Snoqualmie River north of the City of North Bend. The project is scheduled for completion in 2024.
Record Office Revetment Repair The design and construction of this repair project is led by the City of Snoqualmie and repairs 230 feet of damaged bank protection revetment, in order to restore protection of Park Avenue SE.
Reinig Road Revetment Repair This project implements short-term risk reduction measures and permanent repairs of damages to three sections of the Reinig Road Revetment along Reinig Road located between River Mile 41.75 and River Mile 41.84 on the Snoqualmie River.
SR 203 Bridge Improvements Feasibility Study This feasibility study evaluates the opportunities, costs, and benefits of providing increased flood water flow through the SR 203 Bridge and road as you approach the bridge. The study will look at modifications to the existing bridge and/or the addition of culverts or additional bridges north of the existing bridge to reduce flooding on SR 203.
South Fork Skykomish Repetitive Loss Mitigation The repetitive loss program funds elevation or buyout of individual structures in the South Fork Skykomish Basin to eliminate the risk of flooding or erosion damage during future flood events.
Timberlane Village Revetment Repair This project repairs a in Timberlane Village on the South Fork Skykomish River. The revetment is now in poor condition and if left unmodified, the large rocks could fall unexpectedly creating a hazard for people walking along the river and/or cause aquatic degradation.
Tolt River Level of Service Analysis This project conducts a detailed technical analysis to optimize the levels of protection provided by new levee systems in the lower two miles of the Tolt River in order to maximize public safety. The project will also include technical analysis that will investigate project sequencing and the resulting flood effects, both downstream and upstream, that might result.
Tolt River Sediment Management Feasibility Study This project conducts a sediment management feasibility study in order to determine sediment production estimates, evaluate permit and mitigation requirements and if warranted, develop and implement a sediment management plan.
Lower Snoqualmie Valley Residential and Agricultural Flood Mitigation
McElhoe-Pearson Habitat Restoration
Shake Mill Left Bank Flood Risk Reduction Repair
Shake Mill Right Bank Flood Risk Reduction Repair
Sinnema Quaale Upper Revetment Analysis and Repair