Souhegan River Site 35 Dam Reservoir Report

Last Updated: December 16, 2025

Souhegan River Site 35 Dam, also known as Smithville Dam, is a state-owned structure located in New Ipswich, Hillsborough County, New Hampshire.


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Summary

Built in 1965 by the USDA NRCS, this Earth-type dam stands at 30 feet high and spans 1209 feet along the West Branch Souhegan River. Its primary purpose is flood risk reduction, with a storage capacity of 1787 acre-feet and a drainage area of 6.4 square miles.

The dam's hazard potential is classified as high, but its condition assessment as of April 2018 was deemed satisfactory. It is regularly inspected by the NHDES DAM BUREAU, with the last inspection conducted in September 2020. Despite its moderate risk level, the dam has no emergency action plan (EAP) in place, and its risk management measures and inundation maps are currently unprepared. With a maximum discharge capacity of 9135 cubic feet per second, the dam plays a crucial role in managing water flow in the area and protecting downstream communities from flooding events.

Overall, Souhegan River Site 35 Dam serves as a vital piece of infrastructure for flood control along the West Branch Souhegan River. While it faces certain risks and challenges, such as its high hazard potential and lack of an EAP, the dam's satisfactory condition and regular inspections ensure that it continues to fulfill its primary purpose effectively. Its presence highlights the importance of proper dam management and the need for comprehensive emergency preparedness measures to safeguard surrounding areas and communities from potential water-related disasters.

Year Completed

1965

Dam Length

1209

Dam Height

30

River Or Stream

WEST BRANCH SOUHEGAN

Primary Dam Type

Earth

Surface Area

24.9

Drainage Area

6.4

Nid Storage

1787

Outlet Gates

None

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

30
       
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.