Flat Rock Reservoir Report

Last Updated: December 5, 2025

Located in Philadelphia, Pennsylvania, Flat Rock is a state-regulated dam along the Schuylkill River with a primary purpose of recreation.


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Summary

Built in 1977, this concrete dam stands at a height of 21 feet and spans 510 feet in length, providing a storage capacity of 1500 acre-feet. With a normal storage capacity of 788 acre-feet and a surface area of 105 acres, Flat Rock serves as a popular spot for outdoor enthusiasts seeking water-based activities.

Managed by the Pennsylvania Department of Environmental Protection, Flat Rock has a low hazard potential and is assessed to be in fair condition. Regular inspections are conducted every five years to ensure the safety and integrity of the structure. Although the dam does not have a designated spillway type or maximum discharge capacity listed, its association with the Baltimore District of the US Army Corps of Engineers underscores the importance of proper maintenance and monitoring to mitigate any potential risks.

For water resource and climate enthusiasts, Flat Rock presents an intriguing case study in dam management and recreational land use. As a vital piece of infrastructure along the Schuylkill River, this dam showcases the intersection of environmental regulation, public safety, and outdoor recreation. With its historical significance and ongoing maintenance efforts, Flat Rock serves as a reminder of the importance of sustainable water resource management in urban settings like Philadelphia.

Year Completed

1977

Dam Length

510

Dam Height

21

River Or Stream

SCHUYLKILL RIVER

Primary Dam Type

Concrete

Surface Area

105

Drainage Area

1809

Nid Storage

1500

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

21
       
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.