Grub Detention Dam
Grub Detention Dam is a gravity dam located in Valley County, Montana, built in 1964. It carries a Low hazard potential classification and has a unsatisfactory condition assessment.
About Grub Detention Dam
The primary purpose of Grub 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 21 feet tall and stretches 2,339 feet across, creates a reservoir covering 689 acres, has a maximum storage capacity of 4,054 acre-feet, and collects water from a drainage area of 62 square miles. Completed in 1964, 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 unsatisfactory, indicating serious safety deficiencies exist that require immediate attention or remedial action. The most recent inspection on record was 12/02/2019.
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Location
| State | Montana |
| County | Valley |
| Nearest City | Nashua |
| River/Stream | Willow Ck./milk River |
| Coordinates | 48.04626, -106.90734 |
Physical Characteristics
| Dam Type | Gravity |
| NID Height | 21 ft |
| Dam Length | 2,339 ft |
| Year Completed | 1964 (62 years old) |
Storage & Hydraulics
| NID Storage | 4,109 acre-ft |
| Max Storage | 4,054 acre-ft |
| Normal Storage | 4,109 acre-ft |
| Surface Area | 689 acres |
| Drainage Area | 62 sq mi |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | DOI BLM |
| Owner Type | Federal |
| Hazard Classification | Low |
| Condition Assessment | Unsatisfactory |
| Last Inspection | 12/02/2019 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | MT00734 |
| Federal ID | MT00734 |
| More Info | State Dam Safety Program |