O'Farrell Dam No. 1 Reservoir Report
Last Updated: December 13, 2025
O'Farrell Dam No.
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Summary
1, located in Grant, South Dakota, along the TR-N. Fork Whetstone River, was completed in 2005 and stands at a height of 20 feet with a storage capacity of 88 acre-feet. Owned by a private entity and designed by USDA NRCS, this earth dam plays a crucial role in water resource management in the region.
With a low hazard potential and a moderate risk assessment, O'Farrell Dam No. 1 is regulated and inspected by the South Dakota DENR to ensure its structural integrity and safety. The dam features an uncontrolled spillway with a width of 111 feet, capable of handling a maximum discharge of 1070 cubic feet per second, serving as a vital component in flood control and water storage for the surrounding area.
This dam, part of the Omaha District, serves as a testament to the efforts of private owners and state agencies in managing water resources and mitigating the impacts of climate variability in the region. Its presence underscores the importance of proper dam infrastructure in ensuring water security and environmental sustainability for the community it serves.
Year Completed |
2005 |
Dam Length |
400 |
Dam Height |
20 |
River Or Stream |
TR-N. FORK WHETSTONE |
Primary Dam Type |
Earth |
Hydraulic Height |
20 |
Drainage Area |
3 |
Nid Storage |
88 |
Outlet Gates |
None |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
20 |
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.
O'Farrell Dam No. 1