Shasta Dam
Shasta Dam is a concrete arch-gravity dam across the Sacramento River in Northern California in the United States. At 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.
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 26 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. This would produce more low carbon electricity, but is opposed by tribes and fish advocates because of negative impacts from water diversions from river flows and impacts on endangered species.
History
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 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.File:Pit River valley.jpg|thumb|left|upright|The Pit River Valley, now under Shasta Lake, in 1941. The bridge visible near the bottom once carried U.S. Route 99 before it was replaced by the Pit River Bridge.
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 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 infestation between 1919 and 1924 that destroyed 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.
State Water Plan and the CVP
The Marshall Plan was not widely supported due to its high cost ; when proposed to Congress in 1921, it passed in the Senate but failed in the House of Representatives. However, the state of California continued to search for a solution. In 1931, State Engineer Edward Hyatt published a similar but less extensive proposal called the State Water Plan, with a projected cost of about $550 million. Including the dam at Kennett and aqueducts from the Delta southwards into the arid San Joaquin Valley and the Los Angeles Basin, Hyatt's scheme laid the foundations for both the present day Central Valley Project and the California State Water Project.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. Unable to raise the necessary money, California turned to the federal government for help.
In 1935, President Franklin Delano Roosevelt authorized the Central Valley Project as part of the New Deal. The construction works at Shasta Dam and other parts of the project would provide thousands of much-needed jobs, contributing a major portion of the Depression era federal job-creation programs. Roosevelt first considered the U.S. Army Corps of Engineers for building the project, but ultimately transferred it to the Reclamation Service, the precursor to the Bureau of Reclamation, which had expertise in building large concrete dams as demonstrated in the Hoover Dam Project several years earlier. Reclamation chose Frank Crowe, the superintendent of Hoover Dam construction, to direct operations at Shasta Dam.
Construction
Preparations and camps
The groundbreaking and official naming ceremony of Shasta Dam occurred on September 12, 1937 in the small town of Kennett shortly upstream of the dam. Congress initially approved $12 million for the project. Within five years Kennett would be submerged under the rising waters of Shasta Lake. The dam was initially known as Kennett Dam, but was eventually named after nearby Mount Shasta. After surveying several nearby sites, the Bureau of Reclamation chose to build the dam in a deep canyon about a mile above the abandoned smelter town of Coram and two-and-a-half miles below Kennett. The dam was planned to be over high. The winning bid of $35,939,450 for construction came from Pacific Constructors Inc., a conglomerate of 12 smaller companies.Construction started with the excavation of millions of tons of bedrock from the canyon walls adjacent to the construction site, forming keyways for the dam foundations. The Shasta Route of the Southern Pacific Railroad and U.S. Highway 99 were rerouted to the east over the steel truss Pit River Bridge, which remains the tallest combined road and rail bridge in the world. The bridge was built to a height of more than above the Pit River, some east-northeast of the dam site, to accommodate the rising waters of Shasta Lake. The bypassed segment of the railroad from Redding to the Shasta site was re-appropriated as a branch line for construction trains, and was routed through a tunnel beneath the south abutment of the dam.
Reclamation originally planned to set up the construction headquarters in Redding, but ultimately decided to move it closer to the dam site. The new company town, Toyon, was laid out on a farm purchased from Porter Seaman in 1938. Toyon served purely to provide housing for Reclamation personnel, government offices, and storage; no stores or restaurants were permitted within its boundaries. Instead of the tents and shacks typical of construction workers' camps, the town was characterized by comfortable multi-room wooden houses.
Pacific Constructors set up its main camp, called "Contractor's Camp" or "Shasta Dam Village", near the base of the Shasta Dam site. The company built a 2,000-man mess hall, hospital, recreation center and other amenities at the dam site. Three other makeshift camps nearby, called "Central Valley", "Project City", and "Summit City", soon filled with unemployed men from all over the state hoping to get jobs at 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, 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 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 high from its foundations and 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.