Mill Creek Storage Dam

About Mill Creek Storage Dam

The primary purpose of Mill Creek Storage Dam is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by Usace - Walla Walla District (federal). It impounds the Mill Creek Offstream near Walla Walla.

The dam stands 145 feet tall and stretches 3,200 feet across, creates a reservoir covering 25 acres, has a maximum storage capacity of 8,300 acre-feet, and collects water from a drainage area of 80 square miles. Completed in 1942, the structure is well-established, with more than 75 years of service.

This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. An emergency action plan is in place for this dam. The most recent inspection on record was 10/20/2022.

At 145 feet, this dam is taller than 99% of all dams in the United States.

Living Downstream

If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Washington dam safety program can provide more specific information about emergency planning for this structure.

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