Surry Mountain Dam Reservoir Report

Last Updated: December 14, 2025

Surry Mountain Dam, also known as Surry Mountain Lake, is a rockfill dam located in Cheshire County, New Hampshire.


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Summary

Built in 1941 by the US Army Corps of Engineers, the dam stands at a height of 83 feet and has a maximum storage capacity of 44,000 acre-feet. Its primary purpose is flood risk reduction, protecting downstream communities along the Ashuelot River, such as Keene, Swanzey, Winchester, and Hinsdale, from potential flooding events.

Although Surry Mountain Dam significantly reduces the risk of flooding to surrounding areas, there are still moderate risks associated with the dam. The most likely scenario for downstream flooding would be an uncontrolled high volume release of water through the spillway during significant storm events. However, the dam's failure in extreme scenarios, such as the capacity being exceeded or damage to the spillway structure, could result in devastating flooding downstream, impacting towns and cities further along the river, including Hartford, Connecticut. To manage these risks, the US Army Corps of Engineers continually monitors and maintains the dam, works with emergency managers to raise awareness and preparedness, and regularly updates the emergency action plan.

Year Completed

1941

Dam Length

1800

Dam Height

83

River Or Stream

ASHUELOT RIVER

Primary Dam Type

Rockfill

Surface Area

260

Hydraulic Height

77

Drainage Area

100

Nid Storage

44000

Structural Height

83

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

83
       
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.