Half Barrel Detention Dam Reservoir Report
Last Updated: December 21, 2025
Half Barrel Detention Dam, located in Nashua, Montana, is a gravity dam with a primary purpose of fire protection, stock, or small fish pond.
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Summary
Built in 1956 by the Bureau of Land Management, this dam stands at a hydraulic height of 18 feet and a length of 1255 feet, providing a storage capacity of 144 acre-feet. Situated on Willow Creek/Milk River, the dam serves as a crucial resource for water management in the region, with a low hazard potential and moderate risk assessment rating.
Despite its importance, Half Barrel Detention Dam has been marked as unsatisfactory in terms of condition assessment, raising concerns about its long-term stability and functionality. The dam is uncontrolled spillway type with a spillway width of 3 feet, posing potential challenges in handling excess water during periods of high flow. With the last inspection conducted in 2009, there is a pressing need for regular monitoring and maintenance to ensure the safety and efficiency of this vital water resource infrastructure.
As a Federal-owned structure under the supervision of the Bureau of Land Management, Half Barrel Detention Dam plays a key role in water storage and regulation in Valley County, Montana. With its unique design and historical significance, this dam serves as a reminder of the intricate balance between water resource management and climate resilience in the region. Efforts must be made to address the dam's maintenance issues and improve its overall condition to safeguard the surrounding community and environment from potential risks and disruptions.
Year Completed |
1956 |
Dam Length |
1255 |
River Or Stream |
WILLOW CK./MILK RIVER |
Primary Dam Type |
Gravity |
Surface Area |
18.52 |
Hydraulic Height |
18 |
Drainage Area |
1.8 |
Nid Storage |
144 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
18 |
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.
Half Barrel Detention Dam