Hard Rock Detention Dam Reservoir Report
Last Updated: December 20, 2025
Located in Valley County, Montana, the Hard Rock Detention Dam is a gravity dam managed by the Bureau of Land Management.
°F
°F
mph
Wind
%
Humidity
Summary
Completed in 1965, this dam serves the primary purpose of flood risk reduction along the Willow Creek and Milk River. With a hydraulic height of 19 feet and a structural height of 24 feet, the dam has a storage capacity of 440.4 acre-feet and covers a surface area of 63.31 acres.
Despite its low hazard potential, the dam's condition assessment is rated as poor, indicating a need for maintenance and potential upgrades. The last inspection was conducted in November 2019, with a scheduled inspection frequency of 5 years. The risk assessment for the dam is moderate, highlighting the importance of continued monitoring and risk management measures to ensure its safety and effectiveness in mitigating flood risks for the surrounding area.
As an essential infrastructure for flood control in the region, the Hard Rock Detention Dam plays a crucial role in protecting communities and natural resources from potential water-related disasters. With ongoing evaluation and maintenance efforts, this dam continues to serve as a vital asset in managing water resources and climate impacts in the area.
Year Completed |
1965 |
Dam Length |
1307 |
River Or Stream |
WILLOW CK./MILK RIVER |
Primary Dam Type |
Gravity |
Surface Area |
63.31 |
Hydraulic Height |
19 |
Drainage Area |
6.6 |
Nid Storage |
440.4 |
Structural Height |
24 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
24 |
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.
Hard Rock Detention Dam