Larsen Lyman 1 Reservoir Report
Nearby: Larsen Lyman 2 Baysinger Dam
Last Updated: December 13, 2025
Larsen Lyman 1 is a privately owned earth dam located in Pennington, South Dakota, along the TR CHEYENNE river.
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Summary
Built in 1958 and standing at a height of 23 feet, this dam has a storage capacity of 120 acre-feet and a maximum discharge rate of 625 cubic feet per second. While the dam is regulated by the South Dakota Department of Environment and Natural Resources (DENR), it has not been rated for its condition assessment, indicating a low hazard potential.
Managed by the Natural Resources Conservation Service, Larsen Lyman 1 has not undergone recent inspections or evaluations for emergency preparedness. Despite this, the dam is considered to have a low risk potential. While the dam lacks specific risk management measures and emergency action plans, its location in a primarily rural area with limited infrastructure suggests a lower likelihood of catastrophic failure. Water resource and climate enthusiasts may find Larsen Lyman 1 an interesting case study in dam management and potential vulnerabilities in the face of changing environmental conditions.
Year Completed |
1958 |
Dam Length |
300 |
Dam Height |
23 |
River Or Stream |
TR CHEYENNE |
Primary Dam Type |
Earth |
Hydraulic Height |
23 |
Nid Storage |
120 |
Hazard Potential |
Low |
Nid Height |
23 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Cheyenne River Near Wasta
|
190cfs |
Rapid Cr Near Farmingdale Sd
|
53cfs |
Battle Cr Below Hermosa Sd
|
8cfs |
Cheyenne River At Redshirt
|
311cfs |
White R Near Interior Sd
|
50cfs |
Elk Cr Near Elm Springs Sd
|
0cfs |
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.
Larsen Lyman 1