Mt. Elbert Forebay Dam and Reservoir

Halfmoon Diversion Dam

Mt. Elbert Forebay occupies a saddle on a ridge above Twin Lakes Reservoir.  An outlet channel from the southeast corner of the reservoir connects to the inlet-outlet structure for the powerplant penstock.

The rolled earth fill forebay dam is about 2,600 feet long and 92 feet high.  A 130-foot-long earth dike closes a low saddle at the southwest end of the reservoir.  In 1980, the forebay was lined with a 45-mil reinforces chlorinated polyethylene flexible membrane lining material for seepage control. There is no spillway in the forebay dam. There are also no outlet works other than the penstock inlet-outlet structure.  Natural flow into the reservoir is negligible.

The Halfmoon Diversion Dam intercepts the excess flows of Halfmoon Creek for diversion to Mt. Elbert Conduit. The diversion dam consists of a concrete spillway overflow structure, earth-wing dike structures, a gated concrete structure to bypass irrigation flows for downstream use, and a heading for a feeder conduit. The Halfmoon Feeder Conduit is a 60-inch-diameter pipe, 3,202 feet long, and delivers the flow diverted at Halfmoon Creek to the Mt. Elbert Conduit. Flow capacity of the feeder conduit is 150 cfs.

The Mt. Elbert Pumped-Storage Powerplant is on the north shore of picturesque Twin Lakes, approximately 13 miles southwest of Leadville, Colorado. The powerplant was designed with modern architectural lines and is an all concrete structure equivalent to a 14 story building, although most of the structure is below ground.

Power is generated from water stored in the Mt. Elbert Forebay. The water drops 447 feet, spinning the two 138,000 horsepower hydroelectric turbine-generators and developing 200,000 kilowatts of electrical power.

To supplement the flow-through water received from Turquoise Lake through the Mt. Elbert Conduit, these generators have been designed to operate as a 170,000 horsepower electric motor that drives the turbines in reverse, pumping the same water back up to refill the forebay. This pumping mode normally will be used during the very early morning hours, when power demands are low and surplus low-rate power is received from other generating stations. This pump back storage principle is advantageous since the generating unites can be started quickly and adjustments of power output can be made rapidly to respond to varying patterns of daily and seasonal power demands.