Mill Creek Feasibility Study

Project Description

South Skagit Highway, a Skagit County owned road, travels along the South side of the Skagit River and crosses over Mill Creek near milepost 18.

This section of roadway is within the floodplain of the Skagit River and the alluvial fans of Mill and Savage Creeks resulting in routine flooding and damage to the road. The space under the Mill Creek bridge is too small for sediment transport and the Savage Creek culvert is a partial barrier to fish passage. The County began working on this project in 2004 with a sediment and flood management report. In partnership with the Skagit River System Cooperative an alternatives analysis was completed in 2015.

The County and stakeholders identified three alternatives to improve the road and fish passage and habitat in this area. The most cost effective solution is also the best for long-term success. This will require relocating the road to the south. We are currently in the design phase and seeking funding to complete it. We hope to have design completed by 2028 and begin construction in 2029.

Water running over the road from Mill Creek. The creek runs at road level right along the highway.

Mill Creek running onto South Skagit Highway during a flooding event.

FAQ

Why might a realignment be better than leaving the highway in place?

A realignment is a long-term solution that will address the road being within the Skagit River floodplain and the alluvial fan of two creek. Raising the road and bridges leaves it at risk for flooding and damage, costs almost the same as realignment, and would require maintenance. Realignment will also have benefits for fish habitat and salmon recovery, climate impacts, future flooding, and channel migration, making the project more competitive for funding.

What are the next steps for this project?

As of early 2026 the County has identified a preferred alternative and begun collecting data to ensure the relocation is feasible. Next steps for this project include detailed survey downstream, cultural resource exploration, geotechnical work, and finalizing a design. We are continually looking for funding. We have secured funding through conceptual design and intend to have it completed by December 2026. We will be communicating and working with partners and interested parties throughout these processes.

When will construction for this project start?

We do not yet have an estimate for when construction will begin. Construction timing will depend on funding availability and the design process. The earliest possible construction would be 2030.

A map showing that the Mill Creek project is located on the Skagit River just south of State Route 20, between Hamilton and Concrete.

Mill Creek project location.

Project Goals

The overall goals for this project include:

Improving habitat connectivity and floodplain processes for the benefit of threatened Puget Sound Chinook, steelhead, and other salmon species.
Reestablishing fish passage at Mill and Savage Creeks.
Increasing climate change resiliency and reliability of the South Skagit Highway.
Reducing maintenance needs.
Reducing flooding.

Partners, Stakeholders, and Funding

Stakeholders and key partners in and near the project area will be involved throughout the project duration. The project will explicitly involve stakeholders and partners at key points during the decision-making process, including (but not limited to):