Iwan O.M. Number 1 Reservoir Report
Nearby: Iwan #4 Iwan O.M. No.2
Last Updated: December 6, 2025
Iwan O.M.
°F
°F
mph
Wind
%
Humidity
Summary
Number 1 is a privately owned dam located in Mellette, South Dakota, along a tributary of the White River. Constructed in 1970 by the Natural Resources Conservation Service, this earth-type dam stands at 26 feet tall and spans 300 feet in length. With a storage capacity of 45 acre-feet and a maximum discharge of 2100 cubic feet per second, this low-hazard structure plays a crucial role in water resource management in the region.
Despite being regulated by the South Dakota Department of Environment and Natural Resources, the dam's condition is currently listed as "Not Rated," indicating a need for further assessment and monitoring. While it has not undergone recent inspections or been assigned an Emergency Action Plan, Iwan O.M. Number 1 serves as an essential piece of infrastructure for flood control and water supply in the area. As climate change continues to impact water resources, the proper maintenance and assessment of such structures become increasingly vital for ensuring public safety and environmental sustainability.
As water resource and climate enthusiasts, it is important to recognize the significance of dams like Iwan O.M. Number 1 in the context of a changing climate. By supporting ongoing monitoring and maintenance efforts, we can help safeguard our water resources and communities from the threats posed by extreme weather events and shifting hydrological patterns. Collaboration between private owners, regulatory agencies, and concerned citizens will be crucial in ensuring the resilience of our water infrastructure in the face of a rapidly changing climate.
Year Completed |
1970 |
Dam Length |
300 |
Dam Height |
26 |
River Or Stream |
TRIB OF WHITE RIVER |
Primary Dam Type |
Earth |
Hydraulic Height |
26 |
Nid Storage |
45 |
Hazard Potential |
Low |
Nid Height |
26 |
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 1