Cedar Way Stormwater Detention Dam

About Cedar Way Stormwater Detention Dam

The primary purpose of Cedar Way 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 Mountlake Terrace City (local government). It impounds the Lyons Creek near Within Mountlake Terrace.

The dam stands 31 feet tall and stretches 175 feet across, creates a reservoir covering 3 acres, has a maximum storage capacity of 33 acre-feet, and collects water from a drainage area of 1 square miles. Completed in 1985, the structure is 41 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. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 09/21/2021.

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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