Hard Pan Detention Dam Reservoir Report
Last Updated: December 21, 2025
Hard Pan Detention Dam, located in Nashua, Montana, is a Federal-owned structure managed by the Bureau of Land Management.
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Summary
Built in 1954, this gravity dam serves the primary purpose of flood risk reduction along the Willow Creek and Milk River. With a hydraulic height of 18 feet and a structural height of 24 feet, the dam spans 1360 feet and has a storage capacity of 846 acre-feet.
Despite its low hazard potential, the dam's condition assessment is marked as unsatisfactory, warranting regular inspections every five years. The spillway type is listed as uncontrolled with a width of 2 feet, and the dam is associated with an evacuation plan. The risk assessment for Hard Pan Detention Dam is considered moderate, highlighting the need for ongoing risk management measures to ensure the safety and integrity of the structure in the face of potential climate-related challenges.
Water resource and climate enthusiasts will find Hard Pan Detention Dam intriguing due to its historical significance in flood risk reduction efforts in the region. The structure's location in Valley County, Montana, adds to its importance in managing water resources and protecting communities from potential flooding events. As climate change continues to impact water systems, understanding and monitoring dams like Hard Pan Detention Dam become crucial for sustainable water management practices.
Year Completed |
1954 |
Dam Length |
1360 |
River Or Stream |
WILLOW CK./MILK RIVER |
Primary Dam Type |
Gravity |
Surface Area |
176.2 |
Hydraulic Height |
18 |
Drainage Area |
14.6 |
Nid Storage |
846 |
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 Pan Detention Dam