South Anna Dam #4 Reservoir Report
Nearby: Grassdale Dam South Anna No. 5
Last Updated: December 21, 2025
South Anna Dam #4, also known as Allen Lake, is a local government-owned structure in Louisa, Virginia, designed by USDA NRCS and Virginia DCR.
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Summary
Completed in 1981, this Earth-type dam stands at a height of 32 feet and stretches 830 feet in length, with a storage capacity of 2100 acre-feet. Its primary purpose is flood risk reduction along the TR-SOUTH ANNA river. The dam is state-regulated, with inspections and enforcement carried out by the Department of Conservation and Recreation.
Despite being assessed as in fair condition during the last inspection in March 2019, South Anna Dam #4 has a high hazard potential, highlighting the importance of regular monitoring and maintenance. The dam's Emergency Action Plan (EAP) was last revised in January 2013, indicating the need for updated emergency protocols. With a drainage area of 4.27 square miles and a surface area of 20 acres, this dam plays a crucial role in managing water resources and mitigating flood risks in the region.
As a significant infrastructure for flood risk reduction in Louisa, Virginia, South Anna Dam #4 serves as a vital asset for water resource and climate enthusiasts. Its design, construction, and regulatory oversight by state agencies underscore the importance of sustainable water management practices. Continued attention to maintenance and emergency preparedness will ensure the continued efficacy of this dam in safeguarding the community from potential hazards.
Year Completed |
1981 |
Dam Length |
830 |
Dam Height |
32 |
River Or Stream |
TR-SOUTH ANNA |
Primary Dam Type |
Earth |
Surface Area |
20 |
Hydraulic Height |
32 |
Drainage Area |
4.27 |
Nid Storage |
2100 |
Structural Height |
32 |
Hazard Potential |
High |
Nid Height |
32 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
South Anna Dam #4