page_title: Shasta Dam
section_title: Ecological effects
hierarchical_section_title: Shasta Dam / Criticism / Ecological effects
caption_attribution_description: English: View of Shasta Dam in northern California showing the TCD (Temperature Control Device) Reclamation installed in the 1990s to control downriver temperatures for spawning salmon
context_page_description: 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.
  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.
context_section_description: 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 miles (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 1,022 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 1,077 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 of course 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.
caption: The TCD (Temperature Control Device) on the back of the dam, installed in the early 1990s
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