Iwan O.M. No.2 Reservoir Report
Nearby: Iwan #4 Iwan O.M. Number 3
Last Updated: December 6, 2025
Iwan O.M.
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Summary
No.2 is a privately owned dam located in Mellette, South Dakota, with a low hazard potential and a height of 25 feet. Completed in 1961, this earth dam serves as a crucial structure on the tributary of the White River, providing a maximum storage capacity of 19 acre-feet. Despite not being rated for condition assessment, the dam is regulated by the South Dakota Department of Environment and Natural Resources (DENR) and undergoes regular inspections, permitting, and enforcement to ensure its safety and compliance with state jurisdiction.
Situated within the St. Paul District of the US Army Corps of Engineers, Iwan O.M. No.2 plays a vital role in managing water resources in the region, with a maximum discharge capacity of 1000 cubic feet per second. While lacking detailed information on its spillway type and outlet gates, the dam serves multiple purposes such as flood control, irrigation, and water supply management. With Dusty Johnson (R) as the Congressional Representative, the dam remains a significant infrastructure for the local community and contributes to the overall water resource management efforts in South Dakota.
Overall, Iwan O.M. No.2 stands as a testament to the importance of private dams in sustaining water resources and climate resilience. As an essential structure in the region, it highlights the collaboration between private owners, state regulators, and federal agencies in ensuring the safety, functionality, and sustainability of water infrastructure. With ongoing monitoring and maintenance, this dam continues to play a crucial role in supporting the surrounding ecosystem and communities while mitigating potential risks associated with water management.
Year Completed |
1961 |
Dam Length |
370 |
Dam Height |
25 |
River Or Stream |
TRIB. WHITE RIVER |
Primary Dam Type |
Earth |
Hydraulic Height |
25 |
Nid Storage |
19 |
Hazard Potential |
Low |
Nid Height |
25 |
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. No.2