Simmons Lower Reservoir Reservoir Report

Last Updated: December 6, 2025

Simmons Lower Reservoir in Johnston, Rhode Island, is a local government-owned water resource with a high hazard potential.


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Summary

The primary purpose of this gravity dam, completed in 1865, is for other uses, and it stands at a height of 12 feet with a length of 1200 feet. The reservoir has a maximum storage capacity of 317 acre-feet and a normal storage capacity of 264 acre-feet, serving a drainage area of 4 square miles.

Located on Cedar Swamp Brook, this reservoir plays a crucial role in water resource management in Providence County. Despite being state-regulated and inspected, its condition assessment remains unrated as of the last inspection in 2010. With a spillway width of 62 feet and a maximum discharge of 438 cubic feet per second, the Simmons Lower Reservoir presents a vital resource for the local community while also posing potential risks that require proper management and emergency preparedness.

As water resource and climate enthusiasts explore the significance of Simmons Lower Reservoir, its historical importance as a gravity dam serving various purposes underscores the need for regular inspections and risk assessments. With its strategic location and high hazard potential, this reservoir highlights the delicate balance between water management and environmental conservation in the face of changing climate patterns and increasing water demands. As stakeholders continue to monitor and maintain this vital water resource, ensuring its safety and sustainability remains a key priority for the local government and regulatory agencies.

Year Completed

1865

Dam Length

1200

Dam Height

10

River Or Stream

CEDAR SWAMP BROOK

Primary Dam Type

Gravity

Surface Area

49

Hydraulic Height

10

Drainage Area

4

Nid Storage

317

Structural Height

12

Hazard Potential

High

Nid Height

12
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.