Osborn Mills Dam Reservoir Report

Last Updated: December 7, 2025

Osborn Mills Dam, located in Bernards Township, New Jersey, stands as a crucial structure for water supply purposes along the Passaic River.


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Summary

This private-owned Earth dam boasts a height of 15 feet and a length of 250 feet, holding a storage capacity of 100 acre-feet. With a normal storage of 30 acre-feet and a drainage area of 10.2 square miles, the dam plays a pivotal role in regulating water flow and ensuring a stable water supply for the surrounding area.

Despite its significant hazard potential, Osborn Mills Dam has been assessed as satisfactory in condition, with the last inspection conducted in March 2020. The dam's emergency action plan (EAP) was last revised in December 2020, emphasizing the importance of preparedness and risk management. With a maximum discharge capacity of 500 cubic feet per second, the dam's design and structure are meticulously maintained to mitigate potential risks and ensure the safety of downstream communities.

As a vital component of the water resource infrastructure in Somerset County, Osborn Mills Dam serves as a testament to the importance of proper regulatory oversight and routine inspections. The dam's location in Madisonville, New Jersey, highlights its crucial role in water management and underscores the need for continued monitoring and maintenance to safeguard the surrounding communities and environment from potential risks associated with its operation.

Dam Length

250

Dam Height

15

River Or Stream

Passaic River

Primary Dam Type

Earth

Surface Area

10

Drainage Area

10.2

Nid Storage

100

Hazard Potential

Significant

Nid Height

15
       
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.