Little Cohas Brook Dam Reservoir Report
Last Updated: December 16, 2025
Little Cohas Brook Dam, located in Londonderry, New Hampshire, is a concrete structure built in 1953 primarily for recreational purposes.
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Summary
Standing at a height of 10 feet and stretching 70 feet in length, this dam has a storage capacity of 867 acre-feet and serves as a picturesque spot for outdoor activities. The dam overlooks the serene Little Cohas Brook, which has a drainage area of 6.59 square miles and a maximum discharge of 1011 cubic feet per second.
Managed by the NHDES Dam Bureau, this dam has a low hazard potential and fair condition assessment. With a spillway width of 45 feet and uncontrolled spillway type, Little Cohas Brook Dam poses a moderate risk, but this risk is effectively managed through regular inspections and enforcement by the state regulatory agency. The surrounding area offers a surface area of 17 acres for recreational use, making it a popular destination for water resource and climate enthusiasts seeking a tranquil escape in Rockingham County, New Hampshire.
Year Completed |
1953 |
Dam Length |
70 |
Dam Height |
10 |
River Or Stream |
LITTLE COHAS BROOK |
Primary Dam Type |
Concrete |
Surface Area |
17 |
Drainage Area |
6.59 |
Nid Storage |
867 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
10 |
Seasonal Comparison
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Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Little Cohas Brook Dam
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