Rock Cowan No.3 Reservoir Report
Nearby: Rock Cowan No.2 Rock Cowan No. 4
Last Updated: December 7, 2025
Rock Cowan No.3 is a privately owned dam located in Dewey, South Dakota, along the TR-MOREAU river.
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Summary
Built in 1950, this earth dam stands at 22 feet tall and stretches 550 feet in length, with a storage capacity of 280 acre-feet. The dam is regulated by the South Dakota Department of Environment and Natural Resources (DENR), ensuring that it meets state permitting, inspection, and enforcement requirements.
Despite its low hazard potential and current "Not Rated" condition assessment, Rock Cowan No.3 plays a crucial role in water resource management and flood control in the region. With a normal storage capacity of 160 acre-feet and a maximum discharge of 2150 cubic feet per second, this dam serves as a key infrastructure for water supply and mitigation of potential flooding events. As climate change continues to impact water resources, the proper maintenance and regulation of dams like Rock Cowan No.3 are essential for sustainable water management practices.
The St. Paul District of the US Army Corps of Engineers oversees the dam, ensuring its compliance with federal regulations. Despite the lack of specific information on inspections and emergency preparedness, Rock Cowan No.3 remains a vital piece of infrastructure in the region, highlighting the importance of proactive monitoring and maintenance to safeguard water resources and communities against the challenges posed by a changing climate.
Year Completed |
1950 |
Dam Length |
550 |
Dam Height |
22 |
River Or Stream |
TR-MOREAU |
Primary Dam Type |
Earth |
Hydraulic Height |
22 |
Nid Storage |
280 |
Hazard Potential |
Low |
Nid Height |
22 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Moreau R Near Whitehorse Sd
|
35cfs |
Moreau R Near Faith Sd
|
14cfs |
Cheyenne R Near Plainview Sd
|
0cfs |
Grand R At Little Eagle Sd
|
47cfs |
Oak Cr Near Wakpala Sd
|
10cfs |
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.
Rock Cowan No.3