Snoqualmie Flood Reduction Project
also known as Snoqualmie 205 Project
The Snoqualmie Flood Reduction Project was designed to lower flood depths in and around the City of Snoqualmie. The "205 Project" name is a reference to the federal law that allows and funds the U.S. Army Corps of Engineers to participate in this type of project.
Construction status as of June 2004 (827KB pdf)
This air photo shows the historic City of Snoqualmie. The Snoqualmie River flows through town, from the right hand side of this picture to the upper left corner.
The blue lines on this image represent the 100-year floodplain boundary. This floodplain was shaped as a classic "bottleneck", where the narrow rocky river channel above Snoqualmie Falls caused deep and broad flooding in the upstream community. For this reason, the 205 project concentrated on the narrow channel to help reduce flood depths and damages upstream.
The Snoqualmie Flood Reduction Project had three major elements including:
- Rock excavation along the right bank (looking downstream), just upstream of the hydroelectric intake
- Earth excavation along the left bank, just downstream of the SR 202 bridge
- Removal of a partially-failed railroad bridge
This image shows the major project elements along the Snoqualmie River channel in the City of Snoqualmie. The river flows generally to the Northwest. Snoqualmie Falls and its plunge pool are visible in the upper-left corner. Also visible: Fall City-Snoqualmie Road (SR 202) bridge across the river, and new Snoqualmie Parkway (still under construction in this 1996 photo).
The outlines on this air photo show the proposed limit of project excavation. The photo shows Snoqualmie Falls and its plunge pool at the upper left corner. The Salish Lodge is near the top center of the photo, and the SR 202 bridge is at the lower right. As shown, the excavation would extend to nearly the middle of the river channel.
The following documents describe many project details and design needs. These documents were developed for the County Council approval process, which was completed in July of 2002. (Adobe Acrobat).
1. Transmittal Letter from Executive Sims to council
2. WLRD Presentation to council in support of Executive proposal (2.8 Mb)
4. Council Motion (project approval)
The Corps of Engineers and the City of Snoqualmie have entered agreements with King County that specify agency roles and responsibilities for completion of this project. Following are those agency agreements:
All of the required permits were approved and the Corps advertised the project in two separate construction contracts to prospective bidders. The first contract was for channel excavation and the second was for bridge removal. Following is an excerpt of selected plan sheets in .pdf format, as well as links for the complete solicitation on the Corps website.
1. Selected plan sheets (3.0 Mb)
2. Corps solicitation for channel excavation contractor (removed 12/09)
3. Corps solicitation for bridge removal contractor (removed 12/09)
The project was expected to reduce the depth and frequency of flooding in Snoqualmie, where more than 600 homes and most of the commercial area were subject to severe flood damages. The Corps estimated that the project will prevent more than half of the economic damages caused by that flood problem, with an average annual savings of $837,000 (1998 dollars). Total project cost is estimated at $7.65 million, of which the Corps funded $4.40 million (58%).
Because the project moved flood water through the Snoqualmie area more readily, it may have had a small adverse impact on downstream flood problems. This relationship was studied in detail by the Corps of Engineers. Their calculations showed that downstream flooding could become as much as 0.1 foot deeper at the peak of a 100-year flood. Impacts would be smaller during lesser (more frequent) floods, and would diminish with distance from Snoqualmie. Still, this adverse impact is enough that the project included a Downstream Assistance Program (DAP) to help address flood problems where this impact would occur.
The Snoqualmie Flood Reduction Project was proposed by the U.S. Army Corps of Engineers. King County and the City of Snoqualmie shared the local sponsorship responsibilities for this Corps of Engineers project.