Pumped Storage in California | The Center for Land Use Interpretation

The Oroville Dam, in northern California, is the headwaters for the State Water Project, the largest of the statewide hydro engineering projects. It is also the tallest dam in the United States.

There are two pumped storage plants connected to the dam, which are part of the Oroville-Thermalito Complex, a 12-mile-wide engineered waterworks which extends from the Oroville Dam in the east to the Thermalito Afterbay, in the west.

The Oroville-Thermalito Complex is described in the Lake Oroville Visitor Center, located next to the dam.

This is one of three visitor centers in the state that are operated by the California Department of Water Resources. There is another visitor center downstream at the San Luis Reservoir in the Central Valley, and another one at Pyramid Lake, just north of Los Angeles.

These three state run site specific interpretive centers depict and describe the State Water Project, along with some of the linked federal and local projects that collectively make up the largest constructed water supply system in the nation.

The Oroville-Thermalito Complex is at the northern end of the State Water Project, and within the Lake Oroville State Recreation Area, which extends further upstream along the flooded valleys of Lake Oroville.

Lake Oroville captures the flow of the Feather River, as well as tributaries that trickle in from other dams higher up the watershed. It has 167 miles of shoreline, and is the second largest reservoir in the state, after Lake Shasta.

The Oroville Dam is an earth-fill dam, 770 feet high, and took seven years to build. It was dedicated in 1968.

The rainy winter of 2017 caused damage to the spillway, and engaged the use of the additional emergency spillway for the first time since the dam was constructed. This spillway too became damaged, and 180,000 people living below the dam were told to evacuate.

Residents were allowed to return two days later, as reservoir levels declined.

Both spillways were completely reconstructed over the following two years, and a large concrete erosion control apron was built at the top of the emergency spillway.

The reservoir is currently at a very low level, as are most reservoirs in the Southwest.

Though the primary function for the Oroville Dam is as a reservoir to supply water and control flooding, it also generates electricity. The Edward Hyatt Power Plant at the dam produces up to 819 megawatts of power.

The power plant is located inside a 400-foot-long chamber carved inside the rock on the south side of the dam.

The power plant has six generating units, three of which have the ability to reverse, pumping water 600 feet from the base of the dam, back into Lake Oroville.

The upper reservoir intakes/outfalls for the plant are on the south side of the reservoir, connected to the plant through two 22-foot diameter underground penstocks.

Water leaves and enters the plant at the base of the dam in the diversion pool tailrace.

This diversion pool runs for three miles, from the base of dam to the diversion dam.

The diversion dam allows some water to enter the channel of the Feather River, which flows south for 50 miles, then joins the Sacramento River, near the Delta.

The rest of the water continues on through the Thermalito Power Canal to the Thermalito Forebay, and eventually to the Thermalito Dam, five miles further west.

The Thermalito Dam has a powerhouse with four turbines that generate up to 120 megawatts as it lets the water spill into the Thermalito Afterbay.

The Afterbay is a large shallow off-stream terminal reservoir, covering 4,300 acres, created by a low dam that is 42,000 feet long along its south and west sides, flat up against Highway 99.

Three of the turbines in the Thermalito Dam are reversible, and pump water out of the Afterbay, raising the level through the system for ten miles to the Hyatt Plant, which can lift water back up to the Oroville Reservoir, regulating water levels throughout the Oroville Thermalito Complex.

The San Luis Reservoir is a constructed body of water on the western side of the Central Valley.

The reservoir is the main component of the San Luis Complex, which consists of two reservoirs and pump generator plants, and links two statewide aqueduct systems.

The San Luis Reservoir serves as the upper reservoir for a pumped storage project, but its primary function is to store water for federal and state irrigation and drinking water projects.

Covering 12,700 acres, with a capacity of more than 650 billion gallons, it is the largest off-stream reservoir in the nation.

The Romero Visitor Center, a State Water Project interpretive center, is located on a bluff overlooking the reservoir.

This is the smallest and least visited of the three State Water Project interpretive centers, and is often closed for long periods, unannounced.

Outside the building are number of displays, including an impeller from the Dos Amigos Pumping Station on the California Aqueduct.

Plaques commemorate the completion of the reservoir in 1967.

Overlooks provide an extended view of the reservoir, and the intake towers in the dam.

From below, the dam’s scale is hard to reckon, though it is the fourth largest embankment dam in the nation, and is more than 380 feet high.

The William R. Gianelli Pumping-Generating Plant is at the base of the dam. It lifts water 300 feet into the reservoir, and generates as much as 424 megawatts of power when water flows back down through the plant.

The water comes from the lower reservoir, the O’Neill Forebay. This body of water is fed by the California Aqueduct, and the Federal Bureau of Reclamation’s Delta-Mendota Canal.

The O’Neill Forebay has a small pumping-generating plant that lifts water 50 feet up out of the Delta-Mendota Canal, and generates 25 megawatts when it lets water back into it, though it is only occasionally used for this.

The California Aqueduct enters the forebay from the north, and leaves from the south, with gates that regulate its flow in and out.

Stored water leaves the San Luis Reservoir through the Gianelli Plant at the base of the dam and then through the O’Neill Forebay, draining into the California Aqueduct, flowing downstream to Southern California.

The Balsam Meadow Pumped Storage Project is one of two pumped storage hydroelectric projects in the Southern Sierra. It uses a preexisting reservoir as a lower reservoir, a small dedicated upper reservoir, and a power plant between them.

It is located 50 miles northeast of Fresno, near the geographical center of California.

Balsam Meadow is part of the Big Creek Hydroelectric Project, which was developed between 1913 and 1987 to provide power for Los Angeles, and now has six reservoirs, nine power plants, and miles of underground tunnels connecting them.

The Big Creek Project is owned and operated by Southern California Edison, one of a few major energy utilities in California, and generates a total of 1,000 megawatts, which comprises 90% of the company’s hydroelectric generation, and 20% of its total electrical generation.

The pumped storage project was the last component to be built. Construction started in 1983 and ended in 1987, when the upper reservoir at Balsam Meadow was filled.

The reservoir is filled by water pumped up to it from Shaver Lake, or by water flowing down from Huntington Reservoir.

The upper reservoir’s intake/outfall for the pumped storage project is at the top of a 7,500-foot-long tunnel through solid rock, at the base which is the Eastwood Powerhouse, which has one pump turbine unit, with the capacity of generating 200 megawatts.

The Eastwood Powerhouse was named after John S. Eastwood, the engineer who first surveyed the region for development as a hydropower source, starting in the late 1800s, and whose plans were later acquired and developed by Henry Huntington, the Los Angeles railroad magnate.

The plant is accessed through a portal down a closed road, in a cavity carved out of solid granite, 1,000 feet underground.

The Eastwood plant’s lower intake/outfall is at the east end of Shaver Lake, a reservoir constructed as an early part of the Big Creek project. The 180-foot-tall dam was completed 1927.

Shaver Lake is more than a mile above sea level. Water flows out of it through a tunnel near the dam, flowing into a chain of four more power plants before descending into the Central Valley as the San Joaquin River, which flows north for 160 miles, and meets the Sacramento River, at the Delta.

Helms is one of two pumped storage projects in the Southern Sierra. It is owned and operated by Pacific Gas and Electric (PG&E), and is the fifth largest pumped storage project in the country.

The project uses similarly sized upper and lower reservoirs, three miles apart, connected by a tunnel, with an underground pumping power station near the lower reservoir, capable of producing more than 1,200 megawatts.

The area is remote national forest, and has some recreational activity around it, but is otherwise at the end of the road into the mountains, on the edge of the John Muir Wilderness Area.

Courtright Reservoir is the upper reservoir, at 8,100 feet above sea level.

Water level fluctuates dramatically based on water flowing into it from Helms Creek, and from water pumped up to it from below.

The dam forming the reservoir was built in the late 1950s, as part of a string of hydropower plants along the North Fork of the Kings River. It became the upper reservoir for the pumped storage project after four miles of underground tunneling connecting it to the powerhouse and lower reservoir was completed in 1984.

The pumped storage operation was built primarily to provide grid stability in conjunction with the Diablo Canyon Nuclear Power Plant, which PG&E was building at the same time. That plant, 170 miles away on the Central Coast, is now the state’s only operating nuclear power plant.

Next to the dam is an underwater intake/outfall, where water flows through a two-mile-long underground head-race tunnel, controlled by a gate shaft valve with surface facilities above it near the dam.

At the other end, the tunnel curves steeply downward and splits into three penstocks feeding the power plant, 1,625 feet below the level of upper reservoir. The electricity emerges in the substation at the surface, 1,000 feet above the plant, and runs through high-tension lines to another substation near Fresno.

The water then flows through a horizontal tunnel to an intake/outfall at the north end of the Wishon Reservoir, the lower reservoir for the project.

The powerhouse access portal and the intake/outfall are located at the end of a road.

The road is gated and controlled by PG&E.

There is a public overlook nearby with a good view of the lower reservoir.

From here the access portal leading to the underground powerhouse is faintly visible.

There is also a row of interpretive plaques, which discuss the project.

The plaques are sometimes wrapped in plastic to protect them from the elements during the off-season, making them harder to read.

Below the dam, the drainage continues, through another 15 miles of underground tunnels and penstocks, powering four more power plants, mostly built by PG&E in the late 1950s. Together these generate another 335 megawatts of power.

The north fork of the Kings River backs up behind the Pine Flat Dam, at the base of the Sierra, then, after the dam, spreads out to irrigate the Central Valley.

Castaic Lake, on the northern suburban fringe of Los Angeles, is the lower reservoir for the fourth largest pumped storage project in the nation.

The upper reservoir for the project is Pyramid Lake, next to Interstate 5, south of the Grapevine, from which the water flows for more than seven miles through a tunnel to the Castaic Power Plant, on the north end of Castaic Lake.

It is part of the California State Water Project, which brings water from one end of state to the other, drawing Feather River water, from Northern California, to reservoirs around Los Angeles, primarily through the California Aqueduct.

Next to Pyramid Lake is the Vista Del Lago Visitor Center, the third of three State Water Project visitor centers.

Inside, visitors are immersed in an explanatory celebration of the largest hydraulic rejiggering in the nation.

It’s a lot to swallow.

There are touching lessons about how the world of water comes to each of us.

Visitors become one with the flow of water, entering the exhibit hall through a water tunnel-sized portal.

Going with the flow, from north to south.

To Pyramid Lake, gateway to the Southland.

The most evocative displays are outside, where interpretive plaques make a direct connection to the real places above and beyond them, like captions on the world itself.

Water also enters Pyramid Lake from above, from the W. E. Warren Power Plant, bringing water that was pumped over the Tehachapi Mountains, running above and below ground to this point.

On the other side of the dam forming Pyramid Lake, the water flows underground through the Angeles Tunnel.

The Angeles Tunnel is 30 feet wide and has three service access portals along its seven mile length.

The tunnel ends at the surge chamber. The chamber is 120 feet wide and 400 feet tall, most of which is underground. It is used if the Castaic plant has to be shut down suddenly for some reason, absorbing water from the tunnel like a shock absorber.

Penstocks below the chamber run 1,000 feet down to the Castaic Power Plant.

The Castaic Power Plant is capable of generating more than 1,550 megawatts, and pumping all that water up the slope, seven miles back through the tunnel to Pyramid Lake.

Beyond is the Elderberry Forebay, the lower reservoir for the pumped storage plant.

The forebay is an arm of Castaic Lake, the last stop of the west branch of the California Aqueduct, and a major source of water for Los Angeles.

The Lake Hodges Pumped Storage Project is located in San Diego County, in the hills east of Encinitas.

The lower reservoir is Lake Hodges, a dammed portion of the San Dieguito River, and the off-stream upper reservoir is the Olivenhain Reservoir.

Lake Hodges was formed by a dam, which was completed in 1918, and was purchased by the city of San Diego in 1925. Sustained through runoff and rainfall, it was essential to the growth of northern San Diego County.

As San Diego grew, it became dependent on Colorado River water and northern California water, brought to the region by pipelines and aqueducts, and concern mounted about being cut off from imported water by an earthquake or other system failure.

The county established the Emergency and Carryover Storage Project, which included the construction of the Olivenhain Reservoir, to provide more local storage for the region. The new reservoir would in turn feed Lake Hodges.

The Olivenhain Reservoir was built in the hills less than a mile from Lake Hodges, and completed in 2003. It is fed by imported water from the Second San Diego Aqueduct, coming from the north.

The underground pipeline connecting it to Lake Hodges was completed in 2008. A few years later the pumped storage function went online, with a small generating station providing 40 megawatts when water flowed down the pipe.

Water can be pumped back up to the reservoir from the intake/outfall on Lake Hodges.