from Wikipedia
Shasta Dam (called Kennett Dam before its construction) is a curved gravity dam across the Sacramento River in the northern part of the U.S. state of California, at the north end of the Sacramento Valley. The dam mainly serves long-term water storage and flood control in its reservoir, Shasta Lake, and also generates hydroelectric power. At 602 feet (183 m) high, it is the ninth-tallest dam in the United States and forms the largest reservoir in California.
Envisioned as early as 1919 because of frequent floods and droughts troubling California's largest agricultural region, the Central Valley, the dam was first authorized in the 1930s as a state undertaking. However, this coincided with the Great Depression and building of the dam 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 brought about major changes to the environment and ecology of the Sacramento River, and met with controversy over its significant destruction of 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 hydropower generation.
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. Within five years Kennett would be submerged under the rising waters of the lake. Although the dam was originally to be called Kennett Dam, the name was changed to Shasta. Congress approved $12 million for the project. The final site chosen for the dam was in a steep, narrow canyon of the Sacramento River that was nearly 1,000 feet (300 m) deep and located 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 800 feet (240 m) high. The winning bid of $35,939,450 for construction came from Pacific Constructors Inc., a conglomerate of twelve smaller companies.
Construction started with the excavation of millions of tons of bedrock from the canyon walls adjacent to the construction site to provide keyways to lay the dam's foundations. The Shasta Route of the Southern Pacific Railroad, which ran through the site, was rerouted to the east over the steel truss Pit River Bridge, then the tallest double-deck bridge ever built. The bridge was built to a height of more than 500 feet (150 m) above the Pit River, some 7 miles (11 km) east-northeast of the dam site, to accommodate the rising waters of Shasta Lake. The remaining portion of the railroad from Redding to the Shasta site was used as a branch line for construction trains traveling to and from the site, and was routed through a tunnel beneath the south abutment of the dam.
Reclamation originally considered the city of Redding as a good location to set up the headquarters, but due to its distance from the dam site a new planned community called Toyon was constructed, built 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 tents and shacks, the town was characterized by comfortable two, three and four-room wooden houses.
Pacific Constructors, the main company building Shasta Dam, set up its own camp near the base of the Shasta Dam site, called "Contractor's Camp" or "Shasta Dam Village". The company built an enormous 2,000-man mess hall, hospital, recreational center and other venues at the dam site. Three other makeshift camps nearby, called "Central Valley", "Project City", and "Summit City", soon filled with men from all over the state hoping to get jobs at the Shasta Dam as drillers, crane operators, mechanics, truck drivers, carpenters, welders, among others
Foundations
In November 1938, construction started on a diversion channel that would shunt water to the east (left) 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 (15.3 km) 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 (150 kW) 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 (142 m) high from its foundations and 700 feet (210 m) 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
Concrete placement and river diversion
Building of the dam's main concrete structure started in July 1940 after the cable systems had been completed and the mixing plant came on line. Steel buckets capable of carrying 8 cubic yards (6.1 m3) of concrete, weighing 16 tonnes when full, traveled back and forth along the lines. For three years, thousands of men labored building the dam's massive abutments, pouring concrete into large modular "blocks" 50 feet (15 m) square and 5 feet (1.5 m) deep. These blocks were shaped using wooden forms, which were removed when the concrete dried and rebuilt to handle the next block above it. The concrete was "vibrated" into place using specialized equipment, filling in any accidental cavities and bubbles to ensure maximum density and strength. After the concrete dried, the surface was cleaned and smoothed by sandblasting. At the same time, the railroad that ran through the temporary 1,800-foot (550 m) tunnel on the west side of the river was rerouted.
In December 1941, the Japanese attacked Pearl Harbor, prompting the United States to join into World War II. With thousands of men enlisting in the armed forces, the Shasta Dam site soon had a severe labor shortage. During the war years, many of the people who worked at the dam were women and high school students on mostly "non-hazardous jobs". The dam played an important part in World War II even before its completion, supplying much-needed electricity to shipyards and aircraft factories in central California. However, some generators originally intended for Shasta ended up in the Grand Coulee Dam in northern Washington because of the enormous demand of electricity from that dam to power aluminum smelters in the Northwest. The strained supplies and labor forced Reclamation to cut the final height of the dam from 800 feet (240 m) to 602 feet (183 m).
With the tunnel cleared, it was resurfaced and modified to accommodate the force of a river instead of a railroad. Until this time, the Sacramento had still been flowing through the middle of the dam site, between the two nearly completed abutments of the dam. An earth/rock filled cofferdam was constructed across the river, which now began to flow through the tunnel, drying out the dam site and enabling work to begin on the middle section of the dam, which contained the spillway bays. The spillways with their 18 high-pressure river outlet valves and massive triple drum gates were completed in the summer of 1943. By then, a total of 15 million tons of concrete had been used in the dam's construction, comprising the 16,900 50-foot blocks.
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 (4.6 m) 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 (47 m) 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 man-made structure in California. It was also the second most massive 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.)
Design and operations
Shasta Dam serves mainly to provide flood control and carryover water storage for the dry season, contributing greatly to irrigation in the Sacramento Valley and navigation on the Sacramento River, as well as keeping freshwater levels in the Sacramento-San Joaquin Delta high enough for diversion into the California Aqueduct and Delta-Mendota Canal. The dam's other major purpose is to generate hydroelectricity. With a hydraulic head of 330 feet (100 m), the dam is capable of generating 676 megawatts (MW) from five turbines – a pair of 125 MW units and three 142 MW units. Each of the turbines is driven by a high-pressure jet of water fed by a steel penstock 15 feet (4.6 m) in diameter. Two smaller turbines generate power for operations at the dam itself. The plant serves to generate peaking power for the northern Sacramento Valley.[40] Keswick Dam, about 9 miles (14 km) downstream, serves as an afterbay for Shasta, regulating its fluctuating water releases.
A gravity structure, the dam stands 602 feet (183 m) above the foundations with a maximum height of 522.5 feet (159.3 m) above the river. It is 3,460 feet (1,050 m) long, with a maximum thickness of 543 feet (166 m); altogether the dam contains 6,270,000 cubic yards (4,790,000 m3) of material. The dam can release floodwaters through a system of eighteen outlet valves on the face of the spillway. These valves are arranged in three levels, each cutting through the main dam structure and discharging onto the face of the spillway. The upper level has six outlets, each with a capacity of 6,534 cubic feet per second (185.0 m3/s). The middle layer has eight conduits capable of carrying 3,100 cubic feet per second (88 m3/s) and the lowest has four exits each able to discharge 4,450 cubic feet per second (126 m3/s) for a total of 81,800 cubic feet per second (2,320 m3/s). The spillway is a massive concrete chute, 487 feet (148 m) long and 375 feet (114 m) wide, controlled by three 110-foot (34 m)-wide drum gates each weighing 500 US tons (454 t). When the reservoir is full, the gates cannot entirely prevent leakage but can raise the water level up to 28 feet (8.5 m) above the spillway crest. The spillway has a capacity of 186,000 cubic feet per second (5,300 m3/s), bringing the dam's maximum overflow rate to 267,800 cubic feet per second (7,580 m3/s).
The dam forms a reservoir called Shasta Lake, which is the largest man-made lake and third largest body of water in California with its capacity of 4,552,000 acre feet (5,615,000 dam3) and surface area of 29,740 acres (12,040 ha) at maximum pool. The lake extends for 15.3 miles (24.6 km) up the Sacramento River and branches for more than 21 miles (34 km) up the Pit River, which is actually the largest river flowing into the lake. Shasta Lake also has arms of the McCloud River, Squaw Creek, Salt Creek, and scores of other smaller streams that feed it. Shasta Dam controls runoff from a drainage basin of 6,665 square miles (17,260 km2), or about a quarter of the 27,580-square-mile (71,400 km2) Sacramento River watershed.
Tours and recreation
Reclamation holds guided tours of the Shasta Dam year round, each taking two to three hours. There also are a visitor center and auditorium. The tours comprise a 428-foot (130 m) elevator ride to the base of the dam, and visits to the dam's inner galleries and the powerhouse among other areas. Shasta Lake has a surface of 30,310 acres (12,270 ha) at full pool and is surrounded by the Shasta-Trinity National Forest. Many public and private marinas, campgrounds, RV parks, resorts and boat launches border the reservoir, one of the most popular recreational lakes in California. Houseboating, water-skiing, swimming and fishing are among the numerous activities available at the lake; hiking, picnicking, mountain biking, hunting and camping are popular in the mountainous vicinity surrounding it.
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