Gilliland Roy No.1 Reservoir Report
Nearby: Peacock No.1 Anderson No.1
Last Updated: December 13, 2025
Gilliland Roy No.1 is a privately owned earth dam located in Mellette, South Dakota, along the TR Oak Creek offstream.
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Summary
Built in 1960, this dam stands at 28 feet high and stretches 340 feet in length, with a storage capacity of 28 acre-feet. The dam is regulated by the South Dakota Department of Environment and Natural Resources (DENR), with inspection, enforcement, and permitting conducted by state authorities.
Although rated as having low hazard potential and not assessed for condition, Gilliland Roy No.1 serves an important role in water resource management within the region. With a maximum discharge capacity of 278 cubic feet per second, the dam contributes to flood control and water storage in the area. Managed by the Natural Resources Conservation Service, this structure plays a key role in maintaining the ecological balance of the surrounding environment.
Water resource and climate enthusiasts will appreciate the significance of Gilliland Roy No.1 in mitigating potential risks and ensuring the sustainable use of water in South Dakota. The dam's presence highlights the collaborative efforts between private ownership and state regulatory agencies in safeguarding water resources for the benefit of the community. As part of the broader network of dams in the region, Gilliland Roy No.1 underscores the importance of proactive management practices in addressing water-related challenges and promoting environmental resilience.
Year Completed |
1960 |
Dam Length |
340 |
Dam Height |
28 |
River Or Stream |
TR OAK CREEK OFFSTREAM |
Primary Dam Type |
Earth |
Hydraulic Height |
28 |
Nid Storage |
28 |
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.
Gilliland Roy No.1