Overview
The afterbay pool is formed by Yellowtail Afterbay Dam, constructed on the Bighorn River 2.2 miles downstream from Yellowtail Dam. The dam is a 72 ft. high concrete gravity structure with embankment wings. The afterbay dam has a crest length of 1,360 ft. and consists of 21,600 cubic yards of concrete and 162,000 cubic yards of earth material and rip rap. Discharges are used to provide a uniform daily flow into Bighorn River, leveling the peaking power discharges from Yellowtail Powerplant.
Marine sedimentary rock of the Early Cretaceous, know as the Thermopolis shale for the concrete overflow structure. Ten to 15 feet of alluvium overlaying the shale forms the foundation of the embankment wings.
General
Project | Yellowtail Unit, Pick-Sloan Missouri River Basin Program |
Dam Type | Concrete gravity with embankment wings |
Location | 2.2 miles downstream from Yellowtail Dam |
Longitude | -107.92131900787354 |
Latitude | 45.31620533823279 |
Watercourse | Bighorn River |
Reservoir | Yellowtail Afterbay |
Original Construction | 1964-1965 |
National ID Number | MT00582 |
Base Width | 140.00 ft |
Dimensions
Crest Elevation | 3,197.50 ft. |
Structural Height | 72.00 ft |
Hydraulic Height (Normal Operating Depth at Dam) | 36.00 ft |
Crest Length | 1,360.00 ft |
Crest Width | 48.00 ft |
Top of Active Conservation Pool (Elevation) | 3,192.00 ft |
Volume of Dam Construction Materials | 183,600.00 cu yds (concrete, 21,600 cu yds; earth materials and riprap 162,000 cu yds) |
Streambed at Dam Axis | 3,134.00 ft |
Spillway Crest Elevation | 3,192.00 ft |
Hydraulics & Hydrology
Spillway Capacity at Elevation | 3,100.00 cfs at 3,192.00 ft |
Diversion Capacity at Elevation | 750.00 cfs at 3,192.00 ft |
Maximum Water Surface Elevation | 3,141.00 acre-ft at 3,192.00 ft |
Spillway Type | Concrete ogee crest, controlled by five 30- by 13.5-ft radial gates |
Total Water Storage at Elevation | 3,141.00 acre-ft at 3,192.00 ft |
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