Post Lake Dam Reservoir Report
Nearby: W. Day Onida Feeders Dam
Last Updated: December 11, 2025
Post Lake Dam, located in Sully, South Dakota, is a privately owned earth dam that was completed in 1936.
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Summary
With a height of 21 feet and a storage capacity of 344 acre-feet, the dam serves the purpose of regulating water flow in the TR MISSONot RatedI stream. Despite its age, the dam is in good condition with a low hazard potential and is regulated by the South Dakota Department of Environment and Natural Resources.
The dam has not undergone any significant modifications over the years and lacks detailed information on its spillway type and outlet gates. However, it has a maximum discharge capacity of 500 cubic feet per second and a normal storage capacity of 288 acre-feet. While the dam's condition is currently not rated, it is regularly inspected, permitted, and enforced by state regulatory agencies, ensuring its safety and functionality for water resource and climate enthusiasts to appreciate and study.
Post Lake Dam is situated within the St. Paul District of the US Army Corps of Engineers, although it is not directly owned or funded by federal agencies. The dam does not have an Emergency Action Plan in place, but its low hazard potential and good condition suggest that it poses minimal risk to surrounding communities. For those interested in water resource management and climate impact assessment, Post Lake Dam offers a valuable case study in private dam ownership and state regulation, highlighting the importance of infrastructure maintenance and oversight in safeguarding water resources.
Year Completed |
1936 |
Dam Length |
400 |
Dam Height |
21 |
River Or Stream |
TR MISSONot RatedI |
Primary Dam Type |
Earth |
Hydraulic Height |
21 |
Nid Storage |
344 |
Hazard Potential |
Low |
Nid Height |
21 |
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.
Post Lake Dam