Hard Rock Detention Dam
Hard Rock Detention Dam is a gravity dam located in Valley County, Montana, built in 1965. It carries a Low hazard potential classification and has a poor condition assessment.
About Hard Rock Detention Dam
The primary purpose of Hard Rock Detention Dam is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by Doi Blm (federal). It impounds the Willow Ck./milk River near Nashua.
The dam stands 24 feet tall and stretches 1,307 feet across, creates a reservoir covering 63 acres, has a maximum storage capacity of 440 acre-feet, and collects water from a drainage area of 6 square miles. Completed in 1965, the structure is well into its service life at over 50 years old.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. Its condition is rated poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. The most recent inspection on record was 11/02/2019.
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Location
| State | Montana |
| County | Valley |
| Nearest City | Nashua |
| River/Stream | Willow Ck./milk River |
| Coordinates | 47.99630, -107.15844 |
Physical Characteristics
| Dam Type | Gravity |
| NID Height | 24 ft |
| Dam Length | 1,307 ft |
| Year Completed | 1965 (61 years old) |
Storage & Hydraulics
| NID Storage | 440 acre-ft |
| Max Storage | 440 acre-ft |
| Normal Storage | 278 acre-ft |
| Surface Area | 63 acres |
| Drainage Area | 6 sq mi |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | DOI BLM |
| Owner Type | Federal |
| Hazard Classification | Low |
| Condition Assessment | Poor |
| Last Inspection | 11/02/2019 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | MT00742 |
| Federal ID | MT00742 |
| More Info | State Dam Safety Program |