Pohick Creek Dam #1 Reservoir Report

Last Updated: December 5, 2025

Pohick Creek Dam #1, also known as Lake Mercer, is a local government-owned structure located in Fairfax, Virginia, along the South Run stream.


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Summary

With a primary purpose of flood risk reduction, this earth dam stands at a height of 60 feet and spans a length of 1100 feet. The dam has a storage capacity of 4815 acre-feet, with a normal storage level of 1764 acre-feet, covering a surface area of 43 acres and draining a 6.2 square mile watershed.

Managed by the Virginia Department of Conservation and Recreation, Pohick Creek Dam #1 is deemed to have a high hazard potential but is currently in satisfactory condition. It is regularly inspected, with the most recent assessment conducted in October 2020. While the dam has no associated spillways or outlet gates, its construction plays a crucial role in mitigating flood risks for the surrounding area. As a popular recreational spot, Lake Mercer's existence not only safeguards the community but also offers opportunities for outdoor activities and enjoyment.

Dam Length

1100

Dam Height

60

River Or Stream

South Run

Primary Dam Type

Earth

Surface Area

43

Hydraulic Height

60

Drainage Area

6.2

Nid Storage

4815

Structural Height

60

Hazard Potential

High

Nid Height

60
       
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.