Overview
Gibson Dam, the principal structure of Sun River Project, is on the Sun River, 70 miles west of Great Falls, Montana. It is a concrete arch dam 199 feet high and contains 167,500 cubic yards of concrete. A drop inlet spillway located just upstream from the north end of the dam has a capacity of 30,000 cubic feet per second. The entrance to the shaft and 29.5-foot diameter tunnel is controlled by six 34- by 12-foot radial gates. Outlet structures for the dam are two 72-inch diameter semisteel-lined conduits through the base of the dam. The maximum capacity of the outlets is 3,050 feet per second. Gibson Reservoir has a total capacity of 99,100 acre-feet.
Crystalline limestone in regular beds which strike crosswise of river. Special treatment: cement-grout curtain beneath upstream cutoff trench; spring and left abutment grouted.
General
| Project | Sun River |
| Location | On the North Fork of Sun River about 24 miles northwest of Augusta, Montana. |
| Latitude | 47.6013 |
| Watercourse | North Fork of Sun River |
| Original Construction | 1926-1929 |
| Modified Construction | Spillway modified in 1938; outlet works gates replaced in 1971; overtopping modification in 1982 |
| Dam Type | Concrete arch |
| Longitude | -112.7614 |
| Reservoir | Gibson |
| National ID Number | MT00571 |
| Base Width | 117.00 ft |
Dimensions
| Top Parapet (Elevation) | 4,729.00 ft |
| Structural Height | 199.00 ft |
| Crest Length | 960.00 ft |
| Crest Width | 15.00 ft |
| Top of Active Conservation Pool (Elevation) | 4,724.00 ft |
| Volume of Dam Construction Materials | 167,500.00 cu yd |
| Spillway Crest Elevation | 4,712.00 ft |
| Crest Elevation | 4,725.50 ft |
| Hydraulic Height (Normal Operating Depth at Dam) | 195.00 ft |
| Top of Dead Storage Pool (Elevation) | 4,557.50 ft |
Hydraulics & Hydrology
| Spillway Type | Drop-inlet, discharging into shaft and tunnel in left abutment, controlled by 6 34- by 12 - ft radio gates. |
| Spillway Capacity at Elevation | 50,000.00 cfs at 4,729.00 ft |
| Total Water Storage at Elevation | 96,477.00 acre-ft at 4,724.00 ft |
| Outlet Works Capacity at Elevation | 3,050.00 cfs at 4,724.00 ft |
| Maximum Water Surface Elevation | 4,741.00 ft |
Contact
