Mount St. Helens Sediment Retention Structure

About Mount St. Helens Sediment Retention Structure

The primary purpose of Mount St. Helens Sediment Retention Structure 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 - Portland District (federal). It impounds the No. Fork Toutle near Toutle.

The dam stands 239 feet tall and stretches 1,800 feet across, and collects water from a drainage area of 143 square miles. Completed in 1988, the structure is 38 years old.

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 03/10/2022.

At 239 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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