Moccasin Dam is a small dam on Moccasin Creek in

Tuolumne County Tuolumne County (), officially the County of Tuolumne, is a county located in the U.S. state of California. As of the 2020 census, the population was 55,620. The county seat and only incorporated city is Sonora. Tuolumne County comprises the ...

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

, in the town of

Moccasin A moccasin is a shoe, made of deerskin or other soft leather, consisting of a sole (made with leather that has not been "worked") and sides made of one piece of leather, stitched together at the top, and sometimes with a vamp (additional panel o ...

, west of

Yosemite Yosemite National Park ( ) is an American national park in California, surrounded on the southeast by Sierra National Forest and on the northwest by Stanislaus National Forest. The park is managed by the National Park Service and covers an ar ...

. It holds the Moccasin Reservoir. The dam, reservoir and associated hydroelectric power plant are part of the

Hetch Hetchy Project Hetch Hetchy is a valley, a reservoir, and a water system in California in the United States. The glacial Hetch Hetchy Valley lies in the northwestern part of Yosemite National Park and is drained by the Tuolumne River. For thousands of years bef ...

, which provide water and power to the city of

San Francisco San Francisco (; Spanish language, Spanish for "Francis of Assisi, Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the List of Ca ...

. The dam is located near the junction of Highway 120 and Highway 49.

History

In 1914 Congress approved the

Raker Act The Raker Act was an act of the United States Congress that permitted building of the O'Shaughnessy Dam and flooding of Hetch Hetchy Valley in Yosemite National Park, California. It is named for John E. Raker, its chief sponsor. The Act, passed by ...

, allowing San Francisco to construct a dam and reservoir in the Hetch Hetchy Valley of

Yosemite National Park Yosemite National Park ( ) is an American national park in California, surrounded on the southeast by Sierra National Forest and on the northwest by Stanislaus National Forest. The park is managed by the National Park Service and covers an ar ...

for the purpose of public water supply. Due to the large elevation drop between Hetch Hetchy and the city, several hydroelectric power stations were constructed along the long Hetch Hetchy aqueduct. Construction of the Moccasin Powerhouse began in 1921 and was completed on August 14, 1925. The Moccasin Dam was completed in 1930 as a regulating afterbay for the Moccasin Powerhouse. The Moccasin Creek Fish Hatchery was constructed downstream of the dam in 1954, and raises trout for stocking in high elevation streams in the Tuolumne River watershed, and for the nearby, much larger Lake Don Pedro. In 1969, a new powerhouse with more efficient turbines was constructed to replace the original power plant. A March 2018 storm caused the Moccasin Reservoir to become overburdened with water and debris. The dam started to leak and evacuations were issued for a small number of houses and a campground downstream before water levels subsided. Although interim repairs are still ongoing, the California Division of Dam Safety allowed the dam to resume normal operations on June 6, 2019.

Specifications

Moccasin Dam is a rockfill dam, with a structural height of and a length of , containing of material. The elevation at the dam crest is above sea level. The Moccasin Reservoir has a storage capacity of , and a surface area of . The reservoir has a natural

catchment area In human geography, a catchment area is the area from which a location, such as a city, service or institution, attracts a population that uses its services and economic opportunities. Catchment areas may be defined based on from where people are ...

of ; however, most of its water is imported through the Hetch Hetchy Project pipelines. In order to protect the high-quality Hetch Hetchy water, local flows from Moccasin Creek are captured upstream and routed through a bypass system that discharges downstream of Moccasin Dam.Existing Regional Water System
/ref> The bypass includes a small hydroelectric plant with a capacity of 2.9

megawatt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units, International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), ...

s (MW). The main Moccasin Powerhouse is situated at the eastern (upstream) end of the reservoir, and consists of two units with a total capacity of 100 megawatts. In 2004, the powerhouse generated 391 million

Kilowatt hour A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...

s (KWh). In 2009, it generated 348 million KWh. Moccasin is the furthest downstream of San Francisco's three hydroelectric plants (the others are Kirkwood, near Hetch Hetchy Reservoir and Holm near

Cherry Lake Cherry Lake (also known as Lake Lloyd) is an artificial lake in the Stanislaus National Forest of Tuolumne County, California, U.S.A., about east of the city of Sonora. It is at an elevation of on the western side of the Sierra Nevada, and l ...

). Operations at all three plants are coordinated from the control room at Moccasin.

References

{{DEFAULTSORT:Moccasin Dam Dams in California Dams completed in 1930 Rock-filled dams Hydroelectric power plants in California Hetch Hetchy Project Reservoirs in Tuolumne County, California 1930 establishments in California

History

Specifications

See also

References