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Castaic Power Plant (also called Castaic Pumped-Storage Plant) is a seven unit hydroelectric power plant, operated by LADWP, which provides peak load power from the falling water on the West Branch of the California State Aqueduct. It is a cooperative venture between the Los Angeles Department of Water and Power and the Department of Water Resources of the State of California. An agreement between the two organizations was signed on September 2, 1966 for construction of the project.

Location
The Castaic Power Plant is located about 22 miles from the northern Los Angeles city limits at the upper end of the West arm of Castaic Lake.

Water Supply
California State Aqueduct water en route to Southern California is pumped up through the Tehachapi Mountains (by the Edmonston Pumping Plant) to the Tehachapi Afterbay. There the aqueduct divides into East and West Branches. The West Branch water is again pumped at the Oso Pumping Plant to Quail Lake, near Highway 138 East of Gorman. From here it flows through a permanent pipeline waterway to Warne Power Plant, which is located at the inlet to Pyramid Lake. The Warne Plant was constructed by the State of California in 1983. Pyramid Lake has a surface area of 1,380 acres and a storage capacity of 180,000 acre feet with a maximum water surface elevation of 2,578 feet above sea level. Pyramid Lake is the upper forebay for the Castaic Power Plant.

Angeles Tunnel
The State of California had planned to build a tunnel 17 feet in diameter. Under the cooperative development, this tunnel was enlarged to 30 feet in diameter. The 7.2 mile long tunnel, including the penstocks, drops water 1,060 feet between Pyramid Lake and the hydroelectric power facilities, and carries over five times the flow previously contemplated for the 17 foot tunnel.

Surge Chamber
Near the South Portal of the Angeles Tunnel there is a surge chamber which is 120 feet in diameter and 400 feet high. It extends 160 feet above ground level. This tank acts like a giant shock absorber to relieve excess pressure which would be created in the tunnel and penstocks if Castaic Power Plant had an emergency shutdown. The chamber also provides water for rapidly starting the plant while water flow is accelerated in the 7.2 mile long tunnel.

Castaic Power Plant
The Castaic Power Plant has six reversible 250,000 kilowatt main units and one conventional 55,000 kilowatt auxiliary unit. By comparison the largest generators at Hoover Dam are 130,000 kilowatts. The plant rating is 1,247,000 kilowatts (Nominal installed capacity is higher, however when all main units are operating at full load in generate, they are de-rated by friction losses from the water flow in the Angeles Tunnel). The 55,000 kilowatt unit was placed in service in February 1972. The unit also serves as a pump-starting unit for the six reversible units. The first main unit became operational in 1973. Unit six, the last unit, was placed in service in 1978. Power is generated at 18,000 volts then stepped up to 230,000 volts to be distributed to various receiving substations in Los Angeles. The 250,000 kilowatt units function as pumps as well as generators. Each pump will have a power input of 320,000 horsepower when pumping at a rate of 2300 cubic feet per second, or 1,030,000 gallons per minute!

Castaic Reservoir
Water from the Castaic Power Plant is discharged into Elderberry Lake (pumping forebay) from which it can be released into Castaic Lake. Castaic Lake has a surface area of 2,232 acres and a storage capacity of 324,000 acre feet, with a normal maximum surface elevation of 1505 feet above sea level. The amount of water in the lake varies with the demand for water delivery from the West Branch of the State Aqueduct.

Pumped-Storage Operation
The pumping forebay, which is separated from the main reservoir by a dam located downstream from the Castaic Power Plant, functions in connection with the pumped storage operations of the plant. This assures the availability of at least 10,000 acre feet of water which can be pumped back to Pyramid Lake by the use of off peak energy when economical to do so. The pumping function at Castaic hydroelectric plant provides additional water for power generation beyond the supply of water available from the flow of the State Aqueduct. The City of Los Angeles has need for capacity to meet its peak requirements ranging from 3 to 6 hours per day in the winter to 6 to 10 hours per day in summer, depending upon climactic conditions. The water which normally flows through the West Branch of the State Aqueduct during off peak periods, is stored in the higher level Pyramid Lake. This water can be channeled through the turbine generators in a very short time to immediately meet short time peak demands on the DWP's electric system. If the need exists for power for longer than normal peak demand periods, extra water can be pumped back to Pyramid Lake from Elderberry Lake to extend the peaking period.