Jensen No.1 Reservoir Report
Nearby: Atkinson No.1 Winchell Bros. No.1
Last Updated: December 8, 2025
Jensen No.1 is a privately owned dam located in Mellette, South Dakota, along the tributary of Cottonwood Creek.
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Summary
Built in 1965, this earth dam stands at 25 feet tall and stretches 460 feet in length, providing a storage capacity of 21 acre-feet with a maximum discharge rate of 750 cubic feet per second. Despite its low hazard potential, the dam is state regulated and undergoes regular inspections, permitting, and enforcement by the South Dakota Department of Environment and Natural Resources.
Managed by the private owner, Jensen No.1 serves as a crucial water resource structure in the region, offering flood control and water storage benefits to the surrounding area. While the dam is not currently rated for its condition, its structural integrity and risk management practices are consistently monitored to ensure public safety and environmental protection. Additionally, the dam's emergency action plan (EAP) status and risk assessment measures are being evaluated to meet regulatory guidelines and mitigation strategies.
With its strategic location and hydraulic design, Jensen No.1 plays a vital role in the water infrastructure of South Dakota. As part of the St. Paul District, this dam contributes to the sustainable management of water resources and climate resilience in the region. By adhering to state regulations and proactive risk management measures, Jensen No.1 exemplifies the importance of private ownership in maintaining critical infrastructure for the benefit of communities and the environment.
Year Completed |
1965 |
Dam Length |
460 |
Dam Height |
25 |
River Or Stream |
TRIB-COTTONWOOD CREEK |
Primary Dam Type |
Earth |
Hydraulic Height |
25 |
Nid Storage |
21 |
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.
Jensen No.1