Mammoth Pool Dam facts for kids
Quick facts for kids Mammoth Pool Dam |
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 Location of Mammoth Pool Dam in California
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| Country | United States |
| Location | Fresno / Madera counties, California |
| Coordinates | 37°19′23″N 119°18′58″W / 37.32306°N 119.31611°W |
| Construction began | 1958 |
| Opening date | 1959 |
| Dam and spillways | |
| Type of dam | Rockfill |
| Impounds | San Joaquin River |
| Height | 411 ft (125 m) |
| Length | 820 ft (250 m) |
| Width (crest) | 30 ft (9.1 m) |
| Width (base) | 2,100 ft (640 m) |
| Dam volume | 5,250,000 cu yd (4,010,000 m3) |
| Spillways | Ungated overflow |
| Spillway capacity | 170,000 cu ft/s (4,800 m3/s) |
| Reservoir | |
| Creates | Mammoth Pool Reservoir |
| Total capacity | 123,000 acre⋅ft (0.152 km3) |
| Catchment area | 998 sq mi (2,580 km2) |
| Surface area | 1,100 acres (450 ha) |
| Normal elevation | 3,337 ft (1,017 m) (max) |
| Power station | |
| Operator(s) | Southern California Edison |
| Hydraulic head | 1,004 ft (306 m) |
| Turbines | 2x 95 MW |
| Installed capacity | 190 MW |
| Annual generation | 517,987,000 KWh (2001–2012) |
The Mammoth Pool Dam is a large structure that helps make electricity from water. It's built on the San Joaquin River in the Sierra Nevada mountains of California. This dam creates a big lake called Mammoth Pool Reservoir. The dam and the lake are named after a natural pool that used to be there. It's located inside the beautiful Sierra National Forest.
Contents
Building the Mammoth Pool Dam
Early Ideas for Power
Back in 1900, an engineer named John S. Eastwood and some rich investors started a company called Mammoth Power. Their big idea was to use the powerful flow of the San Joaquin River to make electricity. The spot where Mammoth Pool Dam now stands was perfect. The river canyon there was very narrow, with huge walls of solid granite rock.
The first plan was to build a dam that would send water into a long tunnel, about 20 miles (32 km) long. This tunnel would create a huge drop in water level, over 1,700 feet (520 m), to power a 120,000 hp powerhouse. However, the people investing in the project thought it was too big and expensive. So, by 1901, the idea for Mammoth Pool was put on hold.
Construction Begins
Many years later, in the mid-1950s, people started thinking about building hydroelectric power plants in the San Joaquin River area again. Plans for Mammoth Pool Dam and its power station were finally approved.
Building the main dam began in October 1958. First, the San Joaquin River was sent through a 2,150-foot (660 m)-long tunnel to get it out of the way of the construction site. The work went pretty fast. However, the builders faced a challenge: large sheets of granite rock started peeling off the steep canyon walls. This was probably caused by the drilling and explosives used. The dam was finished almost exactly one year later, in late 1959.
What the Dam Does
Making Electricity
The main reason Mammoth Pool Dam exists is to make electricity. It's a very important part of a bigger system called the Big Creek Hydroelectric Project, run by Southern California Edison. This project includes 25 dams, nine power plants, and many tunnels and channels in the upper San Joaquin River area.
Water from the Mammoth Pool Reservoir flows into a 7.45-mile (11.99 km)-long concrete pipe called a penstock. This pipe carries the water to the Mammoth Pool Powerhouse. Inside the powerhouse, there are two large turbines, each with 100,000 horsepower. Together, they can produce about 190 megawatts (MW) of electricity. Because of friction in the long tunnel, the actual power made is usually around 187 MW.
Protecting the Turbines
Just above the powerhouse, there's a 350 ft (110 m) tall structure called a surge chamber. This chamber protects the turbines. If the water flow in the tunnel suddenly changes, like when the power plant quickly turns on or off, the surge chamber helps to balance the water pressure. The power plant gets a huge drop in water level, about 1,004 ft (306 m), which is almost three times taller than the dam itself! This big drop helps create a lot of power.
How Big is the Dam?
Mammoth Pool is a rockfill dam. This means it's made mostly of rocks and earth.
- It stands 411 feet (125 m) tall from its base.
- It is 820 feet (250 m) long.
- The dam rises about 330 ft (100 m) above the San Joaquin River bed.
- It contains a huge amount of material, about 5,250,000 cu yd (4,010,000 m3).
- The top of the dam, called the crest, is at an elevation of 3,361 ft (1,024 m) and is about 30 ft (9.1 m) wide.
- The bottom of the dam is much wider, more than 2,100 ft (640 m) thick.
The Reservoir and Water Flow
The lake behind the dam, Mammoth Pool Reservoir, can hold up to 123,000 acre⋅ft (0.152 km3) of water. Its highest water level can reach 3,337 ft (1,017 m) above sea level.
Normally, water is released from the dam through a special valve that can let out 2,100 cu ft/s (59 m3/s) of water. If there's too much water, it flows over an uncontrolled spillway. This spillway is a channel cut into the rock near the dam. It's 403 ft (123 m) wide and can handle a very large amount of water, about 170,000 cu ft/s (4,800 m3/s).
Impact on Nature
Animals and Their Paths
Mammoth Pool Dam has changed a path that mule deer used to take when they migrated (moved) through the Sierra mountains. Now, they have to swim across the reservoir during their spring and autumn journeys. To protect these deer, the reservoir is closed to all visitors from May 15 to June 15 each year. This helps make sure the deer are not disturbed during their important migration.
River Flow and Fish
During late summer and autumn, almost all the water from the San Joaquin River is sent into the tunnel that leads to the Mammoth Pool power plant. This means that about 9 miles (14 km) of the riverbed below the dam can become almost completely dry. This lack of water has caused a big drop in the number of fish living in that part of the river.
