Statistics: (Cubic Feet per Second = CFS; Mean Sea Level = MSL; Kilowatts = Kw; Revolutions per Minute = RPM)
Significant Dates:
- Operating Since: 1940
- Construction Start: 1933
- Closure: June 24, 1937
- Reservoir filling initiated: November 1937
- Reservoir first reached minimum operating pool: May 27, 1942
- Initial Power Generation – First and Last Units: June 1943 – June 1961
Powerplant
- Number of turbines: 5 Francis,
- Powerhouse #1-2: 128.5 rpm, 1-164 rpm
- Powerhouse#2-2: 128.6 rpm
- Max power generation capability: 185,250 Kw
Size
- Ranking: Largest hydraulically filled dam in the United States, 5th largest reservoir in the United States
- Length of Dam: 21,026 feet (excluding spillway)
- Damming Height: 220 feet (low water to maximum operating pool)
- Maximum Height: 250.5 feet
- Maximum width at base: 4,900 feet (total)
- Maximum width at base: 2,700 feet (without berms)
- Elevation at crest: 2,280.5 feet msl
Construction
- Abutment formations (under dam & embankment): Bearpaw shale & glacial fill
- Type of Fill: Hydraulic & rolled-earth fill
- Amount of Fill: 125,628,000 cubic yards of fill
- Amount of Concrete: 1,200,000 cubic yards
Spillway
- Location: Right bank - remote
- Width: 820 feet gated
- Number of gates: 16
- Dimension of gates: 40-foot x 25-foot vertical lift gates
- Design discharge capacity: 275,000 cfs at 2,253.5 msl pool elevation
- Discharge capacity at maximum operating pool: 230,000 cfs at 2,250 msl
- Top of Spillway Gates (closed): 2,250 feet msl
Intake structures
- Number: 4
- Size: 24-foot 8-inch diameter
- Length:
- Tunnel #1: 5,636.7 feet long
- Tunnel #2: 6,309.5 feet long
- Tunnel #3: 6,614.78 feet long
- Tunnel #4: 7,239.66 feet long
Outlet works
- Number: 4 = 2 lead to powerhouses and 2 are for bypass
- Size: 24-foot 8-inch diameter
- Length: see above tunnel information
- Release capacity: 25,000 CFS/conduit, Combined powerhouses release capacity 15,000 CFS, Total for bypass tunnels and powerhouses is 65,000 CFS
Lake/Reservoir
- Upstream Drainage: 57,500 square miles
- Tributaries: Missouri River, Musselshell River, Fourchette Creek, Dry Creek
- Shoreline length: 1,520 miles at 2,234 feet msl
- Length of full reservoir: 134 miles
- Surface acres: 245,000 acres
- Storage capacity: 18,463,000 acre-feet
- Maximum depth: 220 feet
- Annual Flood Ctrl & Multi-Use Zone (Elevation): 2,234 feet msl – 2,246 feet msl
- Exclusive Flood Ctrl Zone (Elevation): 2,246 feet msl – 2,250 feet msl
- Record Pool Elevation (Date): 2,251.6 feet msl (1975); 2,252.3 feet msl (June 15, 2011)
- Record Flow Prior to 2011 (Year): 35,000 cfs (1975)
- Record Flow (2011): 65,900 cfs (Mid June)