Seven Oaks Dam facts for kids
Quick facts for kids Seven Oaks Dam |
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| Country | United States |
| Location | San Bernardino National Forest, San Bernardino County, near Mentone, California |
| Coordinates | 34°07′02″N 117°06′00″W / 34.11722°N 117.10000°W |
| Construction began | 1993 |
| Opening date | 2000 |
| Construction cost | $450 million |
| Owner(s) | Orange County Flood Control District, San Bernardino County Flood Control District |
| Dam and spillways | |
| Type of dam | Embankment |
| Impounds | Santa Ana River |
| Height | 550 ft (170 m) |
| Length | 2,980 ft (910 m) |
| Reservoir | |
| Creates | Seven Oaks Reservoir |
| Total capacity | 145,600 acre⋅ft (0.1796 km3) |
| Catchment area | 176 sq mi (460 km2) |
| Surface area | 780 acres (320 ha) (max) |
| Normal elevation | 2,604.4 ft (793.8 m) (max) |
The Seven Oaks Dam is a huge earth and rock dam that stands 550-foot (170 m) tall. It crosses the Santa Ana River in the San Bernardino Mountains in southern California. The dam is about 4 miles (6.4 km) northeast of Redlands. It holds back water to create the Seven Oaks Reservoir inside the San Bernardino National Forest.
This dam was planned after big floods happened in the mid-1900s. It was built between 1993 and 2000. Seven Oaks is a special kind of dam called a dry dam. This means it mostly helps stop floods in Orange, Riverside, and San Bernardino Counties. It also collects water to help refill underground water supplies. It is one of the biggest earth dams in the United States. The United States Army Corps of Engineers oversaw its construction. Local flood control groups now own and run the dam.
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Building the Seven Oaks Dam
The U.S. Army Corps of Engineers (USACE) started a big project to improve dams and levees on the Santa Ana River. This was called the Santa Ana River Mainstem Project. One idea was to make the huge Prado Dam bigger. Even when Prado Dam was full, it did not stop all flood damage in Orange County.
Choosing the Best Dam Location
Another plan was to build a new dam, the "Mentone Dam," near Mentone. But this spot caused problems. It would affect how underground water supplies were refilled. People also thought it looked bad. Plus, it was on shaky ground right above the San Andreas Fault. Because people were against it, the USACE changed the plan. They decided to build the Upper Santa Ana River Dam instead. This dam was later named Seven Oaks Dam. It was built in a strong rock canyon about one mile (1.6 km) upstream.
How the Dam Was Built
Work on the Seven Oaks Dam began in May 1994. Workers built a system of conveyor belts, about 3.5 miles (5.6 km) long. These belts could move 3,400 short tons (3,080 t) of material every hour to the dam site. The dirt and rock used to build the dam came from the Santa Ana River canyon below the dam. They also got material from a flat area north of Mentone and a cut in a ridge near the dam. This cut now serves as the dam's spillway.
The dam was built in ten layers using different types of dirt, rock, and clay. In total, about 38,000,000 cubic yards (29,000,000 m3) of material was used. The dam was finished and opened in January 2000. At that time, Seven Oaks Dam was the 12th highest dam in the world. It was also one of the last major dams built in the United States. The final cost of the dam was $450 million, which was more than first expected. The U.S. government paid most of the cost. Orange, San Bernardino, and Riverside Counties paid the rest.
Dam Design and How It Works
Seven Oaks Dam is an arched earth structure that is 2,980-foot (910 m) long. It stands 550 feet (170 m) high above the Santa Ana River. Its deepest parts go down 650 feet (200 m) into the ground. The dam is 40 feet (12 m) wide at the top and over 2,200 feet (670 m) wide at its base. Since it is near the San Andreas Fault, Seven Oaks Dam is built to survive a very strong 8.0 magnitude earthquake.
Reservoir Capacity and Water Release
The reservoir can hold a total of 145,600 acre-feet (0.1796 km3) of water. About 113,600 acre-feet (0.1401 km3) of this is kept for flood control. The rest is for collecting sediment (dirt and sand). When the reservoir is full, the water level is at 2,604.4 feet (793.8 m) high. The water covers an area of 780 acres (320 ha).
Water is let out of the dam through a 1,623-foot (495 m) long tunnel at the bottom. There is also a 500-foot (150 m) wide spillway (an overflow channel) located southeast of the dam. This spillway lets extra water flow out safely. The dam controls water from an area of 176 square miles (460 km2). This area grows to 209 square miles (540 km2) when water from Baldwin Lake also flows into the Santa Ana River during heavy rains.
Flood Protection and Water Benefits
Working with Prado Dam, Seven Oaks Dam helps prevent about $140 million in flood damage each year. It protects over two million people in Orange, Riverside, and San Bernardino Counties. During floods, Seven Oaks Dam holds back water while Prado Dam's reservoir fills up. Then, it releases the water slowly when the river downstream can handle it.
The dam is designed to hold all the water from a "Reservoir Design Flood." This is a very big flood that happens about once every 350 years. It can reduce a flow of 85,000 cubic feet per second (2,400 m3/s) down to 7,000 cubic feet per second (200 m3/s). The dam can even handle an inflow of up to 180,000 cubic feet per second (5,100 m3/s), which is called the "Probable Maximum Flood."
Also, by carefully releasing water, the dam helps refill about 10,000 acre-feet (0.012 km3) of underground water each year. This is good for local water groups because river water costs less than water brought in from other places. Most of the water for farms and cities in the area comes from the California State Water Project.
Dam Performance and Tests
Since it was built, Seven Oaks Dam has not yet been filled to its full capacity. The highest the lake has ever been was about 43,000 acre-feet (0.053 km3) on March 8, 2005. This was less than one-third of its total capacity. This high water gave a chance to test releasing large amounts of water through the dam's tunnel. However, the test had to stop because the strong water flows damaged parts of the concrete tunnel. The tunnel was fixed and successfully tested again in 2011.
Environmental Effects of the Dam
In March 1999, as the dam was almost finished, environmental groups took legal action against the USACE. They said that building the dam had harmed the homes of two rare plants. These plants were the Santa Ana River woolly star and the slender-horned spineflower. The dam also affected the endangered San Bernardino kangaroo rat.
To help these species, the USACE bought 1,547 acres (626 ha) of land next to the dam and reservoir. This land is now used to protect these plants and animals. Also, Seven Oaks Dam has affected the living areas of native fish. This includes the Santa Ana sucker, a fish found only in a few river systems in Southern California.
