South 336th Street Stormwater Dam No 1

About South 336th Street Stormwater Dam No 1

The primary purpose of South 336th Street Stormwater Dam No 1 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 Federal Way City Public Works (local government). It impounds the Hylebos Creek near Fife.

The dam stands 12 feet tall, creates a reservoir covering 6 acres, has a maximum storage capacity of 46 acre-feet, and collects water from a drainage area of 1 square miles. Completed in 1996, the structure is 30 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 05/23/2017. That was 8 years ago, which is on the longer end for a high-hazard structure.

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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