Chase Lake Stormwater Detention Dam

About Chase Lake Stormwater Detention Dam

The primary purpose of Chase Lake Stormwater Detention 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 Snohomish County Public Works - Surface Water (local government). It impounds the Tr-hall Creek near Lynnwood.

The dam stands 10 feet tall and stretches 200 feet across, creates a reservoir covering 5 acres, has a maximum storage capacity of 22 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1990, the structure is 36 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 08/03/2001. That was 24 years ago — unusually long for a high-hazard dam, which typically requires more frequent inspections.

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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