Sunnyside Mp 59.29 Reservoir

About Sunnyside Mp 59.29 Reservoir

The primary purpose of Sunnyside Mp 59.29 Reservoir is irrigation. The dam stores and diverts water for agricultural irrigation, supporting farming operations in the surrounding area. The dam is owned by Sunnyside Valley Irrigation Dist. (public utility). It impounds the Spring Cr Wasteway - Offstream near Prosser.

The dam stands 44 feet tall and stretches 3,800 feet across, creates a reservoir covering 21 acres, has a maximum storage capacity of 400 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 2005, the structure is relatively new.

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 10/13/2021.

At 44 feet, this dam is taller than 90% of dams nationwide.

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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