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Shasta Dam

Quick Read:

Shasta Dam is a concrete arch-gravity dam across the Sacramento River in Northern California. At 602 feet high, it is the eighth-tallest dam in the United States. Envisioned as early as 1919 as an effort to conserve, control, store, and distribute water to the Central Valley, California's main agricultural region, Shasta was first authorized in the 1930s as a state undertaking. However, bonds did not sell due to the onset of the Great Depression and Shasta was transferred to the federal Bureau of Reclamation as a public works project. Tours are available.

Shasta Dam

Shasta Dam - US Bureau of Reclamation

Shasta Dam is a concrete arch-gravity dam across the Sacramento River in Northern California in the United States. At 602 feet high, it is the eighth-tallest dam in the United States. Located at the north end of the Sacramento Valley, Shasta Dam creates Shasta Lake for long-term water storage, flood control, hydroelectricity and protection against the intrusion of saline water. The largest reservoir in the state, Shasta Lake can hold about 4,500,000 acre feet of water.

Envisioned as early as 1919 as an effort to conserve, control, store, and distribute water to the Central Valley, California's main agricultural region, Shasta was first authorized in the 1930s as a state undertaking. However, bonds did not sell due to the onset of the Great Depression and Shasta was transferred to the federal Bureau of Reclamation as a public works project. Construction started in earnest in 1937 under the supervision of Chief Engineer Frank Crowe. During its building, the dam provided thousands of much-needed jobs; it was finished twenty-six months ahead of schedule in 1945. When completed, the dam was the second-tallest in the United States after Hoover, and was considered one of the greatest engineering feats of all time.

Even before its dedication, Shasta Dam served an important role in World War II providing electricity to California factories, and still plays a vital part in the management of state water resources today. However, it has greatly changed the environment and ecology of the Sacramento River, and flooded sacred Native American tribal lands. In recent years, there has been debate over whether or not to raise the dam in order to allow for increased water storage and power generation, a proposal opposed by tribes and environmental experts because of negative impacts from water diversions from river flows needed by endangered fish including salmon species.

Early Proposals

In the late 19th century, the Central Valley was the main destination for large numbers of immigrants traveling into California from the eastern United States. The valley's land was coveted for farming due to its fertile soils, mild climate, gentle topography, and abundant water. The Sacramento River, flows south through the northern third of the valley, known as the Sacramento Valley, for 400 miles before emptying into a vast estuary, the Sacramento-San Joaquin Delta, and ultimately the Pacific Ocean. By the late 1800s, both the valley and Delta regions were intensely cultivated with various crops including wheat, cotton, rice, citrus, and melons.

Shasta DamConstruction

During its building, the dam provided thousands of much-needed jobs; it was finished twenty-six months ahead of schedule in 1945. When completed, the dam was the second-tallest in the United States. Photo courtesy of Bureau of Reclamation.

The low-lying topography of the Sacramento Valley makes it vulnerable to flooding in the winter; conversely, irrigation is necessary during the summer due to the highly seasonal precipitation. Although the Sacramento River discharges nearly 22.4 million acre feet of water each year, most of the flow occurs during winter storms and spring snowmelt, with natural runoff reducing to a trickle during late summers and autumns of drought years. As farming increased, low river flows dropped even lower, leading to saltwater intrusion from San Francisco Bay into the Delta. This caused water shortages for Delta farms, and led to a teredo (saltwater worm) infestation between 1919 and 1924 destroying piers and ships in Suisun Bay.

In a bid to solve the salinity problem, local residents proposed constructing a tidal barrage across the mouth of Suisun Bay, a project which was never realized. In 1919 a different solution came in the form of the Marshall Plan, created by Robert Marshall of the United States Geological Survey. It proposed a large dam across the Sacramento River just downstream of its confluence with the Pit River near the copper mining town of Kennett, several hundred miles to the north of the Delta. The dam would store water for release during the dry months when the Delta was most vulnerable to saltwater intrusion, with the added benefit of controlling floods in the winter. Water captured by the dam would increase the irrigation supply, for both the Sacramento Valley and the San Joaquin Valley further south, with which it would be linked by an extensive aqueduct and reservoir system.

Initially, the state of California intended to finance the project entirely on its own through the sale of revenue bonds. However, the 1930s were a time of economic crisis with the onset of the Great Depression and a severe drought that devastated the agricultural sector, pushing the unemployment rate in California up to 20 percent. The project was approved in the state legislature by a slim margin, mostly riding on Central and Northern California voters, who needed both the jobs and the water. Southern California generally opposed the project because they needed money to build an aqueduct to the Colorado River, from which the state had previously secured rights. In 1933, the state authorized the sale of bonds to fund the Central Valley Project, whose main component was to be Shasta Dam.

Foundations

In November 1938, construction started on a diversion channel that would shunt water to the east side of the river so the foundations could be laid on the west side. The left bank of the river was widened and deepened using explosives, and a cofferdam was built to dry up the bypassed section. To supply sand and gravel to make concrete at the construction site, Pacific Constructors built the largest conveyor belt system in the world, 9.5 miles long, that reached from Redding to the dam site. This was capable of transporting 1,100 tons of material per hour, and over the entire construction process, hauled more than 12 million tons of rock. The belt, which had some 16,000 rollers, was divided into 26 sections, 23 of which were powered by individual 200 horsepower motors. The remaining three were downhill and did not require power; in fact they were retrofitted to generate power for some of the other sections.

As the foundations were completed, concrete placement of the main dam body could begin. For this purpose, a system of steel cable towers was erected to carry the steel concrete-pouring buckets. The tower setup comprised one main tower, standing 465 feet high from its foundations and 700 feet above the river, and seven movable auxiliary towers; cables were strung from the top of the main tower to each of the others. Using this system, construction crews were able to transport concrete from the mixing plant, which lay directly adjacent to the main tower at the end of the conveyor belt, to the rising structure of the dam faster and cheaper than any other method. The tower was not fully demolished, so it remains submerged behind the dam. On occasion, the lake level can drop low enough to expose it again.

Shasta Dam Construction

The last bucket of concrete was poured on January 2, 1945. Photo coutesy of Bureau of Reclamation.

Click here to download a virtual tour of Shasta Dam.

Completion

Water storage at the Shasta Dam began in February 1944 when the diversion tunnel was sealed. As the lake rose behind it, the dam was completed to its final shape and the last bucket of concrete was poured on January 2, 1945. During this time, the Shasta Dam powerplant, with a capacity of 379 MW, was also under construction. Five steel penstocks, each 15 feet in diameter, were installed to provide water to drive the turbines in the power station. The powerhouse was a reinforced concrete structure standing 153 feet above the river; electricity was first generated there in 1944. The dam was completed at the dawn of 1945.

When Shasta was completed, it was the second highest dam in the world - surpassed only by Hoover Dam on the Colorado - as well as the highest human-made structure in California. It was also the second most massive concrete dam measured by volume, exceeded only by Grand Coulee Dam on the Columbia River in Washington. An anonymous workman reportedly said, "Old Shasta's about the secondest dam there is." When the dam was completed, chief engineer Frank Crowe is known to have declared, "Look at that Shasta Dam. That dam will stand there forever holding back the river. And that powerhouse will keep right on turning out juice until somebody discovers how to make power out of sunlight." Ironically, the invention of photovoltaics in the 1950s disproved Crowe's claim, as the Shasta Dam continues to produce as much electricity as ever.

Potential geologic hazards

In a draft geologic technical report prepared pursuant to the planning for modifications of Shasta Dam, the U.S. Bureau of Reclamation cites six types of geologic hazards that have the potential to occur within the project area: seismic hazards, volcanic eruptions and associated hazards, mudflows, snow avalanches, slope instability, and seiches. Seismic hazards stem from the proximity of several fault zones, the nearest being the Battle Creek Fault Zone located approximately 27 miles south of the dam and capable of producing a 7.3 magnitude event. Volcanic hazards are Mount Shasta, Mount Lassen, and the Medicine Lake Highlands.

Shasta Dam Visitor Center

Today's Weather: Shasta Lake, CA

  • Updated: Wednesday, February 24 at 8:10 pm
  • Reporting Station: WHISKEYTOWN HQ#2 (OBRC1)
  • Elevation: 1,360 ft.
  • GPS: 40.610514;-122.527314
  • Data provided by: National Weather Service
53° F
Mostly Clear

Regional Map Forecast Wind: 7 mph (NE)
Humidity: 22%
Dewpoint: 15°F
Barometer: N/A
Visibility: N/A

Tonight: Mostly clear, with a low around 40. North northeast wind 13 to 17 mph, with gusts as high as 26 mph.
Thursday: Sunny. High near 66, with temperatures falling to around 62 in the afternoon. North wind 7 to 15 mph, with gusts as high as 23 mph.

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