O'Neill Dam facts for kids
Quick facts for kids O'Neill Dam |
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O'Neill Forebay and Dam as seen from left bank.
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| Official name | O'Neill Dam |
| Location | Merced County, California, U.S. |
| Coordinates | 37°04′50″N 121°02′50″W / 37.0805°N 121.0472°W |
| Construction began | 1963 |
| Opening date | 1967 |
| Operator(s) | US Bureau of Reclamation |
| Dam and spillways | |
| Impounds | San Luis Creek |
| Height | 87.5 ft (26.7 m) |
| Length | 14,300 ft (4,400 m) |
| Width (base) | 124 ft (38 m) |
| Reservoir | |
| Creates | O'Neill Forebay |
| Total capacity | 56,400 acre⋅ft (69,600 dam3) |
| Catchment area | 18 sq mi (47 km2) |
| Surface area | 2,250 acres (910 ha) |
The O'Neill Dam is a large earthfill dam located in Merced County, California, United States. It sits on San Luis Creek, about 12 miles west of Los Banos, California. This dam is an important part of California's water system.
It creates a body of water called the O'Neill Forebay. This forebay acts like a smaller holding area for water that will later go into the much larger San Luis Reservoir. The O'Neill Dam is located about 2.5 miles downstream from the San Luis Dam.
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Building the O'Neill Dam
The O'Neill Dam was built between 1963 and 1967. It is made from earth and rock, which means it's a huge mound of dirt and stones packed together. The dam stretches for over 3 miles across the valley of San Luis Creek.
The dam is about 87.5 feet tall. Its top, called the crest, is 14,300 feet long. The deepest part of the reservoir behind the dam is 57 feet.
The Morning-Glory Spillway
A special part of the dam is its spillway. A spillway is like a giant drain that lets excess water out of the reservoir safely. The O'Neill Dam has a "morning-glory" type spillway. This means it looks like a huge, inverted bell or a funnel.
This unique spillway can handle a lot of water, about 3,250 cubic feet per second. Its opening has a circumference of 641.5 feet.
O'Neill Forebay: A Water Hub
The O'Neill Forebay is a reservoir created by the O'Neill Dam. It's a key part of how water is managed in this area. Water flows into the forebay from two main sources:
- Releases from the San Luis Dam.
- Water from the Delta–Mendota Canal.
Water from the Delta–Mendota Canal is lifted about 8 feet into a special channel. This channel then carries the water 2,200 feet into the forebay. At its busiest, the forebay can receive 15,600 cubic feet of water per second 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 18 acres.
O'Neill Pumping-Generating Plant
The O'Neill Dam isn't just for holding water; it also helps make electricity! The O'Neill Pumping-Generating Plant is located here. This plant can produce 28 megawatts of power.
The reservoir behind O'Neill Dam holds water that comes from the San Luis Dam and the William R. Gianelli Powerplant. This water is collected in the O'Neill Forebay, which can hold a large amount of water, about 56,400 acre-feet. This stored water is then used to generate electricity.
