Sob Detention Dam Reservoir Report
Last Updated: December 20, 2025
Sob Detention Dam, located in Valley, Montana, serves as a crucial infrastructure for flood risk reduction along Willow Creek and the Milk River.
°F
°F
mph
Wind
%
Humidity
Summary
Built in 1966 by the Bureau of Land Management, this gravity dam stands at a height of 29 feet with a hydraulic height of 23 feet, providing a storage capacity of 190 acre-feet. The dam's primary purpose is flood risk reduction, and it covers a surface area of 24.87 acres with a drainage area of 0.8 square miles.
Despite its low hazard potential, Sob Detention Dam is currently assessed as being in poor condition, highlighting the need for potential maintenance and upgrades to ensure its continued effectiveness in mitigating flooding risks. The dam features an uncontrolled spillway type and has undergone inspections every five years, with the last inspection conducted in November 2019. While the risk assessment for the dam is moderate, ongoing risk management measures and maintenance efforts will be essential to uphold its functionality and safety for the surrounding community in Nashua and beyond.
Year Completed |
1966 |
Dam Length |
600 |
River Or Stream |
WILLOW CK./MILK RIVER |
Primary Dam Type |
Gravity |
Surface Area |
24.87 |
Hydraulic Height |
23 |
Drainage Area |
0.8 |
Nid Storage |
190 |
Structural Height |
29 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
29 |
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.
Sob Detention Dam