Manasquan Reservoir Dam Reservoir Report

Last Updated: December 8, 2025

The Manasquan Reservoir Dam, located in Howell Township, New Jersey, is a vital structure managed by the state for water supply purposes.


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Summary

Completed in 1990, this earth dam stands at a height of 53 feet and spans a length of 4840 feet, holding a maximum storage capacity of 18,470 acre-feet. With a surface area of 770 acres and a drainage area of 3.2 square miles, the dam plays a crucial role in managing water resources in the region.

Situated on Timber Swamp Brook, the Manasquan Reservoir Dam is regulated by the New Jersey Department of Environmental Protection and undergoes regular inspections to ensure its structural integrity. Classified with a high hazard potential, the dam has been assessed as satisfactory in condition, with its last inspection conducted in November 2020. The dam's Emergency Action Plan is in place to address any potential risks, reflecting the state's commitment to safety and efficient water management.

As a key component of the water supply infrastructure in Monmouth County, New Jersey, the Manasquan Reservoir Dam is a testament to effective state regulation and oversight. With its impressive storage capacity and strategic location, the dam serves as a critical resource for maintaining water quality and availability in the region, making it an essential structure for water resource and climate enthusiasts to study and appreciate.

Year Completed

1990

Dam Length

4840

Dam Height

53

River Or Stream

Timber Swamp Brook

Primary Dam Type

Earth

Surface Area

770

Drainage Area

3.2

Nid Storage

18470

Hazard Potential

High

Nid Height

53
       
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.