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 Power Plant.
The spillway consists of an ogee crest controlled by five 30- by 13.5-foot radial gates. The sluiceway is controlled by three 120- by 96-inch cast-iron slide gates with automatic controls.
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
Contact
Owner/Operator
Title: Area Manager Organization: Montana Area Office Address: P.O. Box 30137 City: Billings, MT 59107-0137 Fax: 406-247-7338 Phone: 406-247-7300
Operator
Title: Area Manager Organization: Montana Area Office Address: P.O. Box 30137 City: Billings, MT 59107-0137 Fax: 406-247-7338 Phone: 406-247-7300
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