Moccasin Dam facts for kids
Quick facts for kids Moccasin Dam |
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|---|---|
| Coordinates | 37°48′41″N 120°18′23″W / 37.8113°N 120.3063°W |
| Opening date | 1930 |
| Owner(s) | San Francisco PUC |
| Dam and spillways | |
| Type of dam | Rockfill |
| Impounds | Moccasin Creek |
| Height (foundation) | 60 ft (18 m) |
| Length | 720 ft (220 m) |
| Reservoir | |
| Creates | Moccasin Reservoir |
| Total capacity | 554 acre⋅ft (683,000 m3) |
| Catchment area | 25.4 sq mi (66 km2) |
The Moccasin Dam is a small but important dam in Tuolumne County, California. It's located in the town of Moccasin, just west of the famous Yosemite National Park. This dam creates the Moccasin Reservoir.
The dam, its reservoir, and a nearby power plant are all part of the Hetch Hetchy Project. This big project helps provide water and electricity to the city of San Francisco. You can find the dam close to where Highway 120 and Highway 49 meet.
Contents
Building the Dam: A Look at Its History
In 1914, the United States Congress passed a law called the Raker Act. This law allowed the city of San Francisco to build a dam and reservoir in the Hetch Hetchy Valley. This valley is actually inside Yosemite National Park. The main reason for this project was to supply drinking water to San Francisco.
Because there's a huge drop in elevation between Hetch Hetchy and San Francisco, several power stations were built. These stations use the falling water to create electricity. They are located along the 167-mile (269 km) long Hetch Hetchy aqueduct, which is like a giant pipeline.
Moccasin Powerhouse and Dam Construction
Work on the Moccasin Powerhouse began in 1921. It was finished on August 14, 1925. The Moccasin Dam itself was completed a few years later, in 1930. Its job is to act as a "regulating afterbay" for the Moccasin Powerhouse. This means it helps control the water flow after it has passed through the power plant.
Fish Hatchery and New Power Plant
In 1954, the Moccasin Creek Fish Hatchery was built downstream from the dam. This hatchery raises trout fish. These trout are then released into high-up streams in the Tuolumne River area. They also stock the much larger Lake Don Pedro nearby.
Later, in 1969, a new and improved power plant was built. This new plant uses more efficient turbines to make electricity. It replaced the older power plant.
Dealing with a Storm
In March 2018, a big storm hit the area. The Moccasin Reservoir became very full with water and debris. The dam started to leak, which was a bit scary. People living in a few houses and a campground downstream had to leave their homes for safety. Luckily, the water levels went down, and the situation improved.
Even though some repairs are still being made, the California Division of Dam Safety said the dam could go back to normal operations on June 6, 2019.
How Moccasin Dam Works: Key Features
Moccasin Dam is a type of dam called a rockfill dam. This means it's built mostly from rocks and earth. It stands about 60 feet (18 m) tall and stretches 720 feet (220 m) long. The dam contains about 4,815 cubic yards (3,681 m³) of material. The very top of the dam is about 929.5 feet (283.3 m) above sea level.
Moccasin Reservoir Details
The Moccasin Reservoir can hold about 554 acre-feet (683,000 m³) of water. Its surface covers an area of about 29 acres (12 ha). While the reservoir has a natural catchment area of 25.4 square miles (66 km²), most of its water comes from the Hetch Hetchy Project pipelines.
To keep the Hetch Hetchy water very clean, any local water from Moccasin Creek is collected upstream. It's then sent through a special bypass system. This system releases the creek water downstream of the Moccasin Dam. This bypass even includes a small power plant that can generate 2.9 megawatts (MW) of electricity!
Power Generation at Moccasin
The main Moccasin Powerhouse is located at the eastern end of the reservoir. It has two units that can produce a total of 100 megawatts of power. In 2004, this powerhouse generated 391 million kilowatt-hours (KWh) of electricity. In 2009, it generated 348 million KWh.
Moccasin is the last of San Francisco's three hydroelectric power plants along the Hetch Hetchy system. The other two are Kirkwood (near Hetch Hetchy Reservoir) and Holm (near Cherry Lake). All three of these power plants are managed and controlled from a special control room right at Moccasin.
