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Sauk Valley Road MP 3.7 Improvements
Background
Since 2001, the Skagit River has migrated over 1,200 feet northward along, and parallel to, Concrete-Sauk Valley Road. This channel migration has resulted in the erosion of a high riverbank that is encroaching into the road prism and threatening the necessity of a full lane closure of the road.
After the exceptional flood waters of November 2021 receded, Skagit County Public Works became aware that the Skagit River was migrating significantly towards the Concrete Sauk Valley Road at milepost 3.7. Because previous river migration had occurred on U.S. Forest Service property, the County could only monitor the riverbank until the erosion encroached into the county’s public right-of-way.
Current Work
Over the past two years, regular monitoring of the site has occurred with the rate of bank erosion decelerating. Even so, Public Works continues to plan for the riverbank reaching the public right-of-way, which is when the Department can formally address this erosion issue. Public Works has researched numerous options to control ongoing erosion at this site, but all options must also provide fish habitat features as required by the various permitting agencies. While options to both protect the roadway and protect endangered fish species are available, they are extremely costly.
In recent weeks, Skagit County Public Works crews have shifted the driving lanes of Concrete Sauk Valley Road away from the riverbank to provide additional room for riverbank erosion and a possible construction staging area for future riverbank stabilization work. This will allow at least one lane of the roadway to remain open during construction for any future riverbank stabilization improvements. Construction would take place once permits have been acquired and riverbank conditions exist that require immediate stabilization of the roadway prism.
Drone footage of the new driving lanes below.
What’s Next?
If erosion encroaches into the roadway prism before permitting can be completed, Skagit County will take emergency actions to stabilize the riverbank until the permitted structures can be constructed.
In the long term, the Public Works department is evaluating and applying for funding for a permanent fix to the eroding riverbank. The project would entail installing bank protection measures with an emphasis on using natural materials when feasible, which could include concrete dolosse and large woody debris.
Stabilizing the riverbank is vital to ensuring Concrete Sauk Valley Road remains open and unimpeded to traffic. A closure in this area would require a 32-mile detour, delaying the reliable movement of freight and adding costs for businesses and motorists. A closure would also have a significant impact to the response time of emergency services. This portion of the Skagit River is designated as Wild & Scenic as well as prime habitat for several federally threatened salmon species. The County is committed to managing the road to not impact this fragile ecosystem.
 
| Contact Public Works Engineering
Assistant County Engineer | Engineering Division Manager
Thomas Weller, P.E.
1800 Continental Place
Mount Vernon, WA 98273
Phone: (360) 416-1400
Fax: (360) 416-1405
email: pw@co.skagit.wa.us |
