Hall Mountain Marsh Dam Reservoir Report

Last Updated: December 17, 2025

Hall Mountain Marsh Dam, located in Allenstown, New Hampshire, is a concrete buttress dam primarily used for recreation purposes.


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Summary

Completed in 1950, this dam stands at a height of 13 feet and has a storage capacity of 136 acre-feet. Situated on Bear Brook, the dam has a low hazard potential and is currently in fair condition as of the last assessment in 2012. The dam's spillway type is uncontrolled, with a width of 27 feet, and it has a maximum discharge of 553 cubic feet per second.

Managed by the NHDES Dam Bureau, this state-regulated dam undergoes regular inspections, with the last one conducted in September 2018. Despite its moderate risk assessment rating, the dam has not had an Emergency Action Plan (EAP) prepared or revised recently. The surrounding area has a surface area of 21 acres and a drainage area of 0.43 square miles, making it an important water resource for the region.

For water resource and climate enthusiasts, the Hall Mountain Marsh Dam presents an intriguing case study in dam management and risk assessment. With its unique design and purpose, this dam provides both recreational opportunities and essential water storage capacity. Understanding the complexities of maintaining and regulating such structures is crucial in ensuring the safety and sustainability of our water resources in the face of changing climate patterns.

Year Completed

1950

Dam Length

40

Dam Height

13

River Or Stream

BEAR BROOK

Primary Dam Type

Concrete

Surface Area

21

Drainage Area

0.43

Nid Storage

136

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

13
       
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.