Sandman #1 Reservoir Report
Nearby: Hassett #1 Petrolia
Last Updated: December 6, 2025
Sandman #1 is a privately owned Earth dam located in Petroleum County, Montana, specifically in the city of Mosby.
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Summary
The dam was designed by the USDA NRCS and completed in 1960 for the primary purpose of irrigation. It stands at a height of 20 feet with a length of 450 feet, providing a storage capacity of 52 acre-feet for water from the TR-Box Elder Creek.
Managed and regulated by the Montana Department of Natural Resources and Conservation (DNRC), Sandman #1 has a low hazard potential and has not been rated for its current condition. While the dam has not been inspected in recent years, it is subject to state permitting, inspection, and enforcement to ensure its safety and functionality for irrigation purposes. The surrounding area has a drainage area of 0.47 square miles and a maximum discharge capacity of 150 cubic feet per second.
Located in a remote area, Sandman #1 serves as a crucial water resource for agricultural activities in the region. Its presence contributes to the sustainable management of water for irrigation while adhering to state regulations and safety standards. With its historical significance dating back to the 1960s, the dam continues to play a vital role in water resource management in Montana.
Year Completed |
1960 |
Dam Length |
450 |
Dam Height |
20 |
River Or Stream |
TR-BOX ELDER CREEK |
Primary Dam Type |
Earth |
Hydraulic Height |
20 |
Drainage Area |
0.47 |
Nid Storage |
52 |
Hazard Potential |
Low |
Nid Height |
20 |
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.
Sandman #1