SR 20 Skagit O'Brian Reach Feasibility Study

SR 20 near milepost 101 has experienced frequent embankment erosion and flooding and has required repeated emergency repairs from flood events in the Skagit River. This section of the highway is located below the 10-year flood elevation along a meander of the Skagit River that has been slowly migrating downstream.

For several thousand years, the Skagit River migrated freely across the valley creating an extensive network of sloughs, wetlands, ponds, side channels and other off-channel habitats vital to salmon and other native species. Historic changes to the river altered the natural processes that maintain these floodplain habitats and their connection to the river. The loss of native salmon habitat and impairment of natural processes are major factors in the decline of Chinook, chum, coho and pink salmon, steelhead, bull trout and resident trout in the Skagit River.

Improving salmon and steelhead habitat within Washington’s rivers has become a top priority for public agencies, tribes and private conservation groups, including in the Skagit River.

In November 2017, a small (10-year) flood event in the Skagit River eroded the embankment and destroyed the eastbound lane of SR 20, requiring a two-week closure to rebuild the highway and install emergency bank protection. Although this work was necessary, the large rock typically used in these repairs contributes to degraded fish habitat in the Skagit River. WSDOT has conducted similar repairs to this section of SR 20 many times since 2004, and again in November 2021. Historic damage to this highway is often associated with these smaller, frequent flood events.

WSDOT’s Chronic Environmental Deficiencies (CED) program has been working on a solution to the erosion and flooding problem. The purpose of the CED Program is to proactively implement long-term, nature-based, fish-friendly retrofits at frequent repair sites along WSDOT’s river-adjacent highways. These aim to work with watershed processes that often occur on a large scale.

A large portion of the floodplain of the O’Brian Reach is undeveloped, already dedicated to conservation use and managed by organizations working toward salmon recovery in the basin. This presented an opportunity to collaborate with potential conservation partners on a large-scale approach that addresses both problems, instead of implementing a site-specific solution adjacent to the highway.

Maximizing the value of cooperative partnerships:

In cooperation with our partners and potential partners this study will:

• Engage people and provide opportunities for input on evaluation criteria, potential alternatives, and selection of a feasible alternative, so that the solution is palatable and could result in implementation of a future project.
• Evaluate if floodplain enhancement alternatives that distribute Skagit river flow more broadly across its floodplain would reduce the flooding and scouring flows at the highway embankment. These may include enhancing and reconnecting existing side channels or restoring functional channel patterns on the existing floodplain.
• Evaluate whether these alternatives would increase and diversify rearing habitats by creating shallow stream margins, side channels, and other slow-moving habitats that could benefit juvenile life history phases of almost all species of salmonids.
• Contribute to reducing flooding of other river-adjacent properties and infrastructure.