Iwan No.1 Reservoir Report
Nearby: Highway 44 Highway 44 #6
Last Updated: December 8, 2025
Iwan No.1 is a privately owned Earth dam located in Mellette, South Dakota, along the Pine Creek Offstream.
°F
°F
mph
Wind
%
Humidity
Summary
Completed in 1973, the dam stands at a height of 28 feet and has a storage capacity of 20 acre-feet. With a low hazard potential and a condition assessment that is currently not rated, Iwan No.1 plays a crucial role in water resource management in the area.
Managed by the South Dakota Department of Environment and Natural Resources (DENR), Iwan No.1 is subject to state regulation, permitting, inspection, and enforcement. The dam's primary purpose and associated structures are not specified, but its importance is evident in its role in controlling the flow of water in the region. With a maximum discharge capacity of 435 cubic feet per second, the dam serves as a vital infrastructure for mitigating flood risks and ensuring water security.
Despite its age, Iwan No.1 continues to operate effectively, with no recent inspection data available. As a key component of the water management system in the St. Paul District, the dam contributes to the overall resilience of the region against climate change impacts. With its strategic location and design, Iwan No.1 stands as a testament to the importance of sustainable water resource management in the face of a changing climate.
Year Completed |
1973 |
Dam Length |
300 |
Dam Height |
28 |
River Or Stream |
PINE CREEK OFFSTREAM |
Primary Dam Type |
Earth |
Hydraulic Height |
28 |
Nid Storage |
20 |
Hazard Potential |
Low |
Nid Height |
28 |
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 No.1