Ryno #1 Reservoir Report
Nearby: Allen Tucker No.1 Bruning No.1
Last Updated: December 12, 2025
Located in Mellette, South Dakota, Ryno #1 is a privately owned earth dam completed in 1954 with a height of 30 feet and a length of 211 feet.
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Summary
This dam serves multiple purposes, including flood control and water storage, with a capacity of 36 acre-feet. Positioned on the TR White Thunder Creek offstream, this structure is regulated by the South Dakota Department of Environment and Natural Resources (DENR) and is inspected, permitted, and enforced by state authorities to ensure its safe operation.
Although Ryno #1 has a low hazard potential and is currently rated as "Not Rated" in terms of condition assessment, it lacks an emergency action plan (EAP) and updated contact information for emergency situations. Despite these shortcomings, the dam has not been modified in recent years and remains under the oversight of the St. Paul District of the US Army Corps of Engineers. With a maximum discharge capacity of 130 cubic feet per second, Ryno #1 plays a crucial role in managing water resources in the region and mitigating potential risks associated with flooding.
Year Completed |
1954 |
Dam Length |
211 |
Dam Height |
30 |
River Or Stream |
TR WHITE THUNDER CR OFFSTREAM |
Primary Dam Type |
Earth |
Hydraulic Height |
30 |
Nid Storage |
36 |
Hazard Potential |
Low |
Nid Height |
30 |
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.
Ryno #1