Sully Dam Reservoir Report
Nearby: D. Trumble W. Assmessen
Last Updated: December 7, 2025
Sully Dam, located in Sully, South Dakota, along the Okobojo River, was completed in 1938 by the Works Progress Administration (WPA).
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Summary
This state-regulated earth dam stands at a height of 22 feet and has a storage capacity of 2,640 acre-feet. With a low hazard potential and moderate risk assessment, Sully Dam is crucial for water resource management in the region.
Managed by the state agency DANR, Sully Dam serves multiple purposes, including flood control and irrigation. Despite not having a current condition rating, the dam undergoes inspections every three years to ensure its structural integrity. The spillway, with a width of 120 feet, helps manage maximum discharge levels of 9,040 cubic feet per second, further showcasing the dam's vital role in water management.
With Dusty Johnson (R) as the Congressional representative for this district, Sully Dam plays a significant role in climate resilience and water conservation efforts. As climate change continues to impact water resources, the proper maintenance and management of dams like Sully Dam are essential to safeguarding communities and ecosystems in the face of evolving environmental challenges.
Year Completed |
1938 |
Dam Length |
1470 |
Dam Height |
22 |
River Or Stream |
OKOBOJO |
Primary Dam Type |
Earth |
Hydraulic Height |
22 |
Nid Storage |
2640 |
Outlet Gates |
None |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
22 |
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.
Sully Dam