O'Neill Forebay facts for kids
Quick facts for kids O'Neill Forebay |
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O’Neill Forebay and Dam as seen from left bank
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 O'Neill Forebay
Location in California
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| Location | Merced County, California |
| Coordinates | 37°05′00″N 121°02′33″W / 37.0832°N 121.0426°W |
| Type | Reservoir |
| Primary inflows | California Aqueduct Delta–Mendota Canal San Luis Reservoir |
| Primary outflows | California Aqueduct |
| Catchment area | 18 acres (7.3 ha) |
| Basin countries | United States |
| Max. length | 3 km (1.9 mi) |
| Max. width | 3 km (1.9 mi) |
| Surface area | 2,250 acres (910 ha) |
| Max. depth | 17 m (56 ft) |
| Water volume | 56,400 acre-feet (69,600 dam3) |
| Shore length1 | 19 km (12 mi) |
| Surface elevation | 71 m (233 ft) |
| 1 Shore length is not a well-defined measure. | |
The O'Neill Forebay is a special type of reservoir in Merced County, California. It acts like a smaller holding area for the much larger San Luis Reservoir. This forebay was created when the O'Neill Dam was built across San Luis Creek. You can find it about 12 miles (19 km) west of Los Banos, California, on the eastern side of the California Coast Ranges.
How O'Neill Forebay Works
The O'Neill Forebay is located about 2.5 miles (4 km) downstream from the San Luis Dam. It collects water that flows out from the San Luis Dam and the William R. Gianelli Powerplant. This helps manage the water flow. The forebay can hold a lot of water, about 56,400 acre-feet.
Water also enters the forebay from two important canals: the California Aqueduct and the Delta–Mendota Canal. Water from the Delta–Mendota Canal is lifted about 8 feet (2.4 m) into a channel. This channel then carries the water about 2,200 feet (670 m) into the forebay. There is a special "morning-glory" shaped spillway on the left side of the reservoir. This spillway helps release extra water safely.
Building the O'Neill Dam
The O'Neill Dam was built between 1963 and 1967. It is an earthfill and rockfill dam, meaning it's made from packed earth and rocks. The dam is about 87.5 feet (26.7 m) tall and stretches over 3 miles (4.8 km) across the San Luis Creek valley.
The deepest part of the reservoir behind the dam is about 57 feet (17 m). A lot of water can flow into the forebay, up to 15,600 cubic feet (440 cubic meters) per second. This water comes from both the San Luis Dam and the Delta–Mendota Canal. The area that drains into the reservoir downstream of the San Luis Dam is quite small, only about 18 acres (7.3 hectares). The O'Neill Pumping-Generating Plant, located here, can store 28 megawatts hours of energy.
Fun Activities at O'Neill Forebay
O'Neill Forebay is a popular spot for recreation, especially for fishing.
The California Office of Environmental Health Hazard Assessment (OEHHA) has given advice about eating fish caught here. This is because small amounts of mercury and PCBs have been found in some fish. The advisory helps people know which fish species are safe to eat and how much.
A very famous fish was caught in the O'Neill Forebay! The largest striped bass ever caught in California was pulled from these waters. It was caught on August 5, 2008, by Frank Ualat from Gilroy, California. This amazing fish was 52.5 inches (133 cm) long and weighed a huge 70.6 pounds (32.0 kg)!
