Blackwater Dam - Little Hill Dike Reservoir Report

Last Updated: December 19, 2025

Blackwater Dam - Little Hill Dike, also known as the Dry Reservoir, is a federal-owned structure located in Webster, New Hampshire.


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Summary

Built in 1941 by the US Army Corps of Engineers, this gravity dam stands at a height of 38 feet and has a storage capacity of 93,400 acre-feet. It primarily serves the purpose of flood risk reduction along the Blackwater River, with a spillway width of 241 feet to manage water levels during high flow events.

The dam's hazard potential is considered high, and while the condition assessment is not available, an Emergency Action Plan (EAP) is in place to address any potential risks. The USACE continuously monitors the dam's health and engages with local emergency managers to ensure preparedness in case of a dam-related emergency. Regular maintenance and repairs are conducted to keep the dam in proper working order, and risk management measures are implemented to mitigate potential flood risks.

With a drainage area of 128 square miles and a maximum discharge capacity of 42,800 cubic feet per second, Blackwater Dam - Little Hill Dike plays a crucial role in managing water flow and reducing flood risks in the region. The USACE's proactive approach to risk management and emergency planning ensures the safety and protection of communities downstream, highlighting the importance of sustainable water resource management and climate resilience.

Year Completed

1941

Dam Length

1425

Dam Height

38

River Or Stream

BLACKWATER RIVER

Primary Dam Type

Gravity

Surface Area

1

Hydraulic Height

33

Drainage Area

128

Nid Storage

93400

Structural Height

38

Hazard Potential

High

Nid Height

38
       
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.