Yellowtail Afterbay Dam

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
RegionFacilities in Great Plains | Great Plains Home Page
StateMontana
CountyBig Horn
ProjectYellowtail Unit, Pick-Sloan Missouri River Basin Program
Dam TypeConcrete gravity with embankment wings
ReservoirYellowtail Afterbay
WatercourseBighorn River
Location 2.2 miles downstream from Yellowtail Dam
Longitude-107.92131900787354
Latitude45.31620533823279
Original Construction1964-1965
Modified Construction
National ID NumberMT00582
Hydrologic Unit Code

Dimensions
Structural Height72.00 ft
Hydraulic Height (Normal Operating Depth at Dam)36.00 ft
Top Parapet (Elevation)
Spillway Crest Elevation3,192.00 ft
Crest Elevation3,197.50 ft.
Crest Length1,360.00 ft
Crest Width48.00 ft
Base Width140.00 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
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)
Top of Active Conservation Pool (Elevation) 3,192.00 ft
Top of Inactive Conservation Pool (Elevation)
Top of Dead Storage Pool (Elevation)

Hydraulics & Hydrology
Total Water Storage at Elevation3,141.00 acre-ft at 3,192.00 ft
Maximum Water Surface Elevation3,141.00 acre-ft at 3,192.00 ft
Normal Water Surface Elevation
Spillway TypeConcrete ogee crest, controlled by five 30- by 13.5-ft radial gates
Auxiliary Spillway
Spillway Capacity at Elevation3,100.00 cfs at 3,192.00 ft
Auxiliary Spillway Capacity at Elevation
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation
Diversion Capacity at Elevation 750.00 cfs at 3,192.00 ft
Drainage Area
Hydrometeorological Report (HMR)
Probable Maximum Flood (PMF) Report

Contact Information
Owner
TitleArea Manager
OrganizationMontana Area Office
AddressP.O. Box 30137
CityBillings, MT 59107-0137
Phone (Fax)406 247-7338
Phone (Office)406 247-7300
Operator
TitleArea Manager
OrganizationMontana Area Office
AddressP.O. Box 30137
CityBillings, MT 59107-0137
Phone (Fax)406 247-7338
Phone (Office)406 247-7300


Last updated: Apr 02, 2013