Manor Lake Dam Reservoir Report

Last Updated: December 10, 2025

Manor Lake Dam, located in Morris County, New Jersey, is a local government-owned structure that serves to regulate the flow of the Whippany River.


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Summary

This earth dam stands at a height of 5 feet and spans 125 feet in length, with a storage capacity of 9 acre-feet. The dam is under the regulatory authority of the New Jersey Department of Environmental Protection (NJDEP) and is subject to regular inspections to ensure its satisfactory condition.

Despite its relatively modest size, Manor Lake Dam poses a significant hazard potential due to its location and the potential impact of a dam failure on downstream areas. However, as of the last inspection in 2020, the dam was deemed to be in satisfactory condition. The emergency action plan (EAP) for the dam was last revised in 2015, indicating a commitment to preparedness and risk management. The dam does not fall under the jurisdiction of the US Army Corps of Engineers.

Water resource and climate enthusiasts may find Manor Lake Dam to be a fascinating subject for study, given its role in managing water flow in the Whippany River watershed. Understanding the design, operation, and regulatory oversight of dams like Manor Lake can provide valuable insights into the broader challenges of water resource management and climate resilience. As efforts continue to address aging infrastructure and enhance dam safety nationwide, Manor Lake Dam serves as a microcosm of the complex interplay between human-made structures, natural water systems, and the need for sustainable practices in a changing climate.

Dam Length

125

Dam Height

5

River Or Stream

Whippany River

Primary Dam Type

Earth

Surface Area

4

Drainage Area

1.5

Nid Storage

9

Hazard Potential

Significant

Nid Height

5
       
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.