Simmons Upper Reservoir

About Simmons Upper Reservoir

The primary purpose of Simmons Upper Reservoir is debris control. The dam is designed to catch sediment, rocks, and debris carried by flowing water — particularly important in areas prone to mudslides or heavy erosion. The dam is owned by Johnston, Town Of (local government). It impounds the Cedar Swamp Brook near Johnston.

The dam stands 16 feet tall and stretches 650 feet across, creates a reservoir covering 48 acres, has a maximum storage capacity of 430 acre-feet, and collects water from a drainage area of 3 square miles. Completed in 1865, the structure is one of the older dams in the region, with over a century and a half of service.

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 poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. Notably, no emergency action plan is currently on file for this high-hazard dam.

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 Rhode Island dam safety program can provide more specific information about emergency planning for this structure.

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