Derry Robert No.1 Reservoir Report
Nearby: Dimond Wendell No. 1 Ryno #2
Last Updated: December 13, 2025
Derry Robert No.1 is a privately owned dam located in Mellette, South Dakota, along the White Thunder Offstream river.
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Summary
Built in 1965, this earth-type dam stands at a height of 28 feet and has a length of 444 feet. With a storage capacity of 43 acre-feet and a maximum discharge of 432 cubic feet per second, this dam serves as a vital water resource for the surrounding area.
Managed by the Natural Resources Conservation Service, Derry Robert No.1 is regulated by the South Dakota Department of Environment and Natural Resources (DENR). Despite being classified as having a low hazard potential, the dam's condition has not been rated, and there is no available information on its inspection frequency or emergency action plan preparedness. However, with its important role in water storage and management, it remains a key infrastructure for the region's water resources and climate resilience efforts.
As an integral part of the water infrastructure in South Dakota, Derry Robert No.1 plays a crucial role in regulating water flow and providing essential water storage for the area. With its strategic location and design, this dam serves as a valuable asset for water resource and climate enthusiasts, highlighting the importance of efficient water management and infrastructure maintenance for sustainable development in the region.
Year Completed |
1965 |
Dam Length |
444 |
Dam Height |
28 |
River Or Stream |
WHITE THUNDER OFFSTREAM |
Primary Dam Type |
Earth |
Hydraulic Height |
28 |
Nid Storage |
43 |
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.
Derry Robert No.1