Iwan O.M. Number 3 Reservoir Report
Nearby: Iwan O.M. No.2 Iwan #4
Last Updated: December 6, 2025
Iwan O.M.
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Summary
Number 3 is a privately owned earth dam located in Mellette, South Dakota, along the TR White River Offstream. Completed in 1960, this dam stands at 27 feet high with a length of 240 feet, providing a storage capacity of 29 acre-feet. Managed by the Natural Resources Conservation Service, this structure is regulated by the South Dakota Department of Environment and Natural Resources, ensuring proper inspection, permitting, and enforcement measures are in place.
Despite its low hazard potential and current "Not Rated" condition assessment, Iwan O.M. Number 3 plays a crucial role in water resource management in the area. With a maximum discharge of 312 cubic feet per second, this dam helps regulate water flow and storage for the surrounding watershed. While specific emergency preparedness details are not provided, the dam's presence highlights the importance of maintaining infrastructure to mitigate potential risks and ensure the safety of downstream communities.
As climate change continues to impact water resources, structures like Iwan O.M. Number 3 become vital in adapting to changing conditions. Understanding the role of dams in water management and the need for ongoing monitoring and maintenance is essential for sustaining water security in the face of evolving environmental challenges.
Year Completed |
1960 |
Dam Length |
240 |
Dam Height |
27 |
River Or Stream |
TR WHITE RIVER OFFSTREAM |
Primary Dam Type |
Earth |
Hydraulic Height |
27 |
Nid Storage |
29 |
Hazard Potential |
Low |
Nid Height |
27 |
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.
Iwan O.M. Number 3