Шеста Дам на реке Сакраменто: История и современность

Dam in California, US

Shasta Dam (called Kennett Dam before its construction) is a concrete arch gravity dam across the Sacramento River in Northern California in the United States. At 602 feet (183 m) 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. 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. 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.

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 mile (644 km) 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. 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 (saltwater worm) 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.

The Marshall Plan was not widely supported due to its high cost (about $800 million in 2008 dollars); 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 (CVP) and the California State Water Project (SWP). 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. 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 (Boulder Canyon) Project several years earlier. Reclamation chose Frank Crowe, the superintendent of Hoover Dam construction, to direct operations at Shasta Dam.

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 1000 feet (305 m) 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 800 feet (244 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, forming keyways for the dam foundations. 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.

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, 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 465 feet (142 m) high from its foundations and 700 feet (213 m) above the river, and seven movable auxiliary towers; cables were strung from the top of the main tower to each of the others. 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.

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 of concrete, weighing 16 tons 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 (2 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, which filled 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 1800 feet (549 m) tunnel on the west side of the river was rerouted. In December 1941, the Japanese attacked Pearl Harbor, prompting the United States to enter 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, working 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 for 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 (244 m) to 602 feet (183 m).

In a draft geologic technical report prepared pursuant to the planning for modifications of Shasta Dam, the U. S. Bureau of Reclamation cites (p. 27) 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.

The Shasta Dam has had a severe negative effect on populations of Pacific salmon in the Sacramento River watershed ever since its gates were first closed in 1943. The massive structure completely prevents salmon migration from the lower reaches of the river to the Upper Sacramento, Pit, McCloud and other tributary streams. It is estimated that half of the best salmon habitat in the Sacramento basin lies upstream of Shasta Dam. Also, the dam caused temperatures in the river to rise because it released waters from higher elevations of Shasta Lake, which are warmed by the sun far more than the surface of the original river pre dam. Warm waters are harmful to salmon, which prefer colder temperatures, and also impact other fish populations such as steelhead and wild California trout. In an attempt to save the plunging salmon populations, the federal government constructed the Coleman National Fish Hatchery on Battle Creek in 1942. The hatchery is situated approximately 20 mile (32 km) southeast of Redding, and produces 13,850,000 eggs per year – nearly 87 percent of which are for the fall chinook salmon run. Another remedy was carried out by the Bureau of Reclamation in 1991, with the installation of a gigantic facility called a TCD (Temperature Control Device) on the rear face of Shasta Dam. This structure enables dam operators to decide the depth of the reservoir from which the water feeding into the penstocks originates. As one progresses deeper into Shasta Lake, the water gets colder where it receives less sunlight. The TCD is equipped with fifteen openings called "shutters" arranged in rows along the back face of the structure. The rows lie 1022 feet (312 m), 922 feet (281 m), and 817 feet (249 m) above sea level. (The crest of Shasta Dam is at an elevation of 1077 feet (328 m).) The system has shown significant success in reducing the temperature of the Sacramento River below the dam, although it does exhibit leakage. As for the health of the river overall, the dam has indirectly affected it by promoting the growth of cities and farms along it. However, construction of the dam also has had direct consequences to the morphology and vegetation zones along the river. By raising summer flows much higher than their natural average, and moderating the effects of most floods, the post dam river supplies an even amount of water to the riparian zone each year, and resultantly vegetation has encroached on the river channel. The dam has vastly reduced the amount of sediment in the Sacramento, and the riverbanks now suffer decreased erosion, slowing the growth of meanders and side channels. Additionally, nearly all the rock and sand used in the mixing of concrete for the dam was dredged from the river downstream of the dam, further depleting its sediment supply.

Underneath the waters of Shasta Lake lie buried the traditional lands of the Winnemem Wintu, one of nine groups of the larger Wintu ethnicity of northern California. The Winnemem Wintu tribe is considered to be a ghost tribe because they are not a federally recognized tribe. It is estimated that the pre colonization population of the valley was roughly 14,000; by 1900, due to diseases and settlers' encroachment it was reduced to 395. Of the men who survived out of the 395, many fought in the U. S. armed forces during World War II. When they returned in 1945, they found their family members driven out of their traditional villages by the rising waters of Shasta Lake. More than 90 percent of their original land was lost, and the ten percent that remains now lies along the lower McCloud River. On May 1 of 1941, the United States Congress passed the Central Valley Project Indian Lands Acquisition Act, to take ownership of the homes and lands of the Winnemem Wintu people. Scores of village sites, burial sites and other sacred locations now sit several hundred feet below the surface of Shasta Lake. Over 27 sacred sites lie underneath the water behind the dam. Tribal members argue that several reservation treaties originally set by the U. S. government in the 1850s were later broken so the filling of Shasta Lake could proceed; afterwards, only a tiny fraction of that land remained theirs. Furthermore, the Winnemem are not recognized by the federal government, an omission that they have been seeking to rectify for over a century. Recently, native hostility to the dam has heightened because of the proposals to raise it – which would drown twenty of the remaining sacred sites, including Children's Rock and Puberty Rock, both used in coming of age ceremonies, and a burial place for victims of the Kabyai Creek Massacre. The tribe conducted a war dance in September 2004 for the first time in 117 years in opposition of the dam and Reclamation's raising project; the event reputedly inspired many environmental groups to support the tribe's position.

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 feet (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 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.