Trinity Dam

Trinity Dam
Country United States
Location Whiskeytown-Shasta-Trinity National Recreation Area, Trinity County, California
Coordinates 40°48′04″N 122°45′48″W / 40.80111°N 122.76333°W / 40.80111; -122.76333Coordinates: 40°48′04″N 122°45′48″W / 40.80111°N 122.76333°W / 40.80111; -122.76333
Construction began 1957
Opening date 1962
Owner(s) U.S. Bureau of Reclamation
Dam and spillways
Type of dam Earthfill
Impounds Trinity River
Height 538 ft (164 m)
Length 2,450 ft (750 m)
Spillway type Morning glory
Spillway capacity 22,400 cu ft/s (630 m3/s)
Reservoir
Creates Trinity Lake
Total capacity 2,447,650 acre·ft (3,019,130 dam3)
Inactive capacity 400,000 acre·ft (490,000 dam3)[1]
Catchment area 692 sq mi (1,790 km2)
Surface area 17,722 acres (7,172 ha)
Power station
Hydraulic head 426 ft (130 m)
Turbines 2x Francis
Installed capacity 140 MW
Annual generation 359 million KWh

Trinity Dam is an earthfill dam on the Trinity River located about 7 miles (11 km) northeast of Weaverville, California in the United States. The dam was completed in the early 1960s as part of the federal Central Valley Project to provide irrigation water to the arid San Joaquin Valley.

Standing 538 ft (164 m) high, Trinity Dam forms Trinity Lake – California's third largest reservoir, with a capacity of more than 2,400,000 acre feet (3,000,000 dam3). A hydroelectric plant at the base of the dam furnishes power to surrounding rural areas, and the reservoir also provides flood control benefits to the Trinity River valley. However, controversy has surrounded the negative impacts of the dam project on the river's salmon run.

Background

In response to the Great Depression and drought conditions in California during the early 20th century, the United States Congress passed the 1935 Rivers and Harbors Act, which authorized the Central Valley Project (CVP) – a system of dams and canals to provide a stable supply of irrigation water to California's Central Valley.[2] Among the project works was a 1942 proposal to divert water from the Trinity River in northwestern California to augment water supplies in the CVP service area, known as the Trinity River Division. However, the state dropped the Trinity River project from the CVP in 1945.[3]

Six years later, however, the U.S. Bureau of Reclamation (USBR), which was responsible for the construction and operations of most CVP facilities, revived the division, which comprised a system of four dams and two tunnels to capture and store the flow of the Trinity and transport it to the Sacramento River, generating a net surplus of hydroelectric power along the way. Trinity Dam was to be the main storage feature of the division, providing a stable flow to the Lewiston Dam, the diversion point for Trinity River waters into the Central Valley.[3][4]

Construction

Construction at Trinity Dam began on June 4, 1956 with preliminary excavation and the river was diverted around the dam site on July 8, 1957. Work was bogged down in late 1957 when the river flooded and took out the cofferdam that protected the construction site. However, workers cleared out the dam site by the summer of 1958, and the hiatus also allowed them time to line the diversion tunnel with concrete.[3]

Rock placement began on the main structure as early as 1957, but it was not until 1959 when a 11,000 ft (3,400 m) conveyor belt was incorporated, allowing much faster transport of fill to the dam site. The spillway tunnel was completed in October 1959 and the embankment was topped out in late 1960. The dam's power plant, however, was not finished until December 1963. Trinity stood as the highest earthfill dam in the world until eclipsed by the Oroville Dam, also in California, in 1968.[3] The latter remains the tallest dam in the United States.[5]

As the reservoir filled, it submerged the pioneer towns of Trinity Center, Stringtown and Minersville as well as parts of a historic Northern California stagecoach route.[6] The reservoir was originally named Clair Engle Lake after Clair Engle, a United States senator and major proponent of the CVP. This name was unpopular among local residents, many of whom had watched their homes inundated by the rising waters. By 1995, it had been renamed Trinity Lake.[7]

Specifications

Overview of Trinity Dam complex showing the spillway to the left and powerhouse in right center

Trinity Dam is an earth and rock-filled dam composed mainly of river gravel and local rock, rising 538 ft (164 m) from its foundations and 440 ft (130 m) above the riverbed. The dam's crest is 2,450 ft (750 m) long and 2,395 ft (730 m) above sea level.[8] High water releases are controlled by three different sets of gates. The outlet works have a capacity of 24,000 cu ft/s (680 m3/s), and the service spillway, a morning-glory (bell-mouth) design, can take 22,400 cu ft/s (630 m3/s) of water. The dam's auxiliary spillway has a capacity of 2,250 cu ft/s (64 m3/s).[9]

Trinity Lake can hold up to 2,447,650 acre feet (3,019,130 dam3) at full pool, and encompasses up to 17,722 acres (7,172 ha) of water.[10] Trinity Powerplant, located at the base of the dam, has two Francis turbines with a capacity of 140 megawatts (MW) combined, uprated from an original capacity of 100 MW. The plant generates an average of 358.97 million kilowatt hours (KWh) and has a low capacity factor, which means it operates mainly on a peaking basis.[11]

Environmental impacts

Trinity Dam forms an impassable barrier for migrating salmon in the Trinity River, but along with other division facilities has also had adverse impacts on salmon habitat in the lower reaches of the river. Within ten years of the dam's completion, more than three-quarters of Trinity River water was being diverted to the Central Valley each year, and the little flow left in the river was warm, shallow and less suitable for spawning salmon. In addition, the dam blocks the Trinity River's annual floods and sediment loads, leading to degradation in the gravel bars that are vital for salmon habitat.[12][13]

In response to declining salmon populations, the USBR built the Trinity River Fish Hatchery. The hatchery is operated by the California Department of Fish and Game and has a capacity of 40 million eggs.[4] In 1992, Congress passed the Central Valley Project Improvement Act, which established a minimum annual release of 340,000 acre feet (420,000 dam3) into the lower Trinity River.[14]

Recreation

With 145 miles (233 km) of shoreline,[15] Trinity Lake is a popular summer destination for Northern California residents. Since 1965, the lake has been part of the Trinity Unit of the Whiskeytown-Shasta-Trinity National Recreation Area. The lake has been developed with boat ramps and marinas, most of which are concentrated in the Stuart Fork arm in the southwest and around the resort town of Trinity Center near the north end of the reservoir.[16]

See also

References

  1. ↑ Ritzema, Randall S.; Newlin, Brad D.; Van Lienden, Brian J. (October 2001). "Appendix H: Infrastructure" (PDF). CALVIN Project. University of California Davis. Retrieved 2014-01-25.
  2. ↑ "Central Valley Project". U.S. Bureau of Reclamation. 2011-04-21. Retrieved 2012-02-12.
  3. 1 2 3 4 Stene, Eric A. (1996). "Trinity Division: Central Valley Project". U.S. Bureau of Reclamation. Retrieved 2012-02-12.
  4. 1 2 "Shasta/Trinity River Division Project". Central Valley Project. U.S. Bureau of Reclamation. 2011-04-21. Retrieved 2012-02-12.
  5. ↑ "Oroville Dam and Lake Oroville". California State Water Project. California Department of Water Resources. 2009-06-17. Retrieved 2012-02-12.
  6. ↑ Jones, Carolyn (2011-09-12). "Anger lingers over towns flooded by Trinity Dam". San Francisco Chronicle. Retrieved 2012-02-12.
  7. ↑ "Designation of Trinity Lake" (PDF). 104th Congress, 1st Session. U.S. Government Printing Office. 1995-06-07. Retrieved 2012-02-12.
  8. ↑ "Trinity Dam: Dimensions". Shasta/Trinity River Division Project. U.S. Bureau of Reclamation. 2009-06-04. Retrieved 2012-02-12.
  9. ↑ "Trinity Dam: Hydraulics & Hydrology". Shasta/Trinity River Division Project. U.S. Bureau of Reclamation. 2009-06-04. Retrieved 2012-02-12.
  10. ↑ "Trinity Dam". National Performance of Dams Program. Stanford University. Retrieved 2012-02-12.
  11. ↑ "Trinity Powerplant". Shasta/Trinity River Division Project. U.S. Bureau of Reclamation. 2001-04-04. Retrieved 2012-02-12.
  12. ↑ "Upper Trinity River Population" (PDF). SONCC Coho Salmon Recovery Plan. National Oceanic and Atmospheric Administration. January 2012. Retrieved 2012-02-12.
  13. ↑ "Background". Trinity River Restoration Program. Retrieved 2012-02-12.
  14. ↑ "Trinity River Restoration Program Overview" (PDF). CVPIA Annual Work Plan. U.S. Bureau of Reclamation. 2011-02-17. Retrieved 2012-02-12.
  15. ↑ "Trinity Lake – Bureau of Reclamation". Recreation.gov. Retrieved 2012-02-12.
  16. ↑ "Trinity Unit" (PDF). Whiskeytown-Shasta-Trinity National Recreation Area. U.S. Forest Service. 2003. Retrieved 2012-02-12.

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