Rainbow
Rainbow is an other dam located in Cascade County, Montana, built in 1910. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Rainbow
The primary purpose of Rainbow is hydroelectric. The dam generates hydroelectric power by channeling water through turbines, converting the energy of flowing water into electricity. The dam is owned by Northwestern Energy (private). It impounds the Missouri River near Fort Benton.
The dam stands 44 feet tall and stretches 1,405 feet across, creates a reservoir covering 126 acres, has a maximum storage capacity of 1,237 acre-feet, and collects water from a drainage area of 22,928 square miles. Completed in 1910, the structure is over a century old.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 08/10/2022.
At 44 feet, this dam is taller than 90% of dams nationwide.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Montana dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Montana |
| County | Cascade |
| Nearest City | Fort Benton |
| River/Stream | Missouri River |
| Coordinates | 47.53430, -111.20520 |
Physical Characteristics
| Dam Type | Other |
| NID Height | 44 ft |
| Dam Height | 44 ft |
| Dam Length | 1,405 ft |
| Year Completed | 1910 (116 years old) |
Storage & Hydraulics
| NID Storage | 1,237 acre-ft |
| Max Storage | 1,237 acre-ft |
| Normal Storage | 1,237 acre-ft |
| Surface Area | 126 acres |
| Drainage Area | 22,928 sq mi |
| Max Discharge | 125,000 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Hydroelectric |
| Owner | NorthWestern Energy |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 08/10/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | MT00557 |
| Federal ID | MT00557 |
| More Info | State Dam Safety Program |