New Melones Dam

New Melones Dam
Country	United States
Location	Near Jamestown, California
Coordinates	37°56′50″N 120°31′41″W / 37.94722°N 120.52806°W / 37.94722; -120.52806Coordinates: 37°56′50″N 120°31′41″W / 37.94722°N 120.52806°W / 37.94722; -120.52806
Construction began	1966
Opening date	1979
Dam and spillways
Type of dam	Earth and rock embankment
Impounds	Stanislaus River
Height	625 ft (191 m)[1]
Length	1,560 ft (480 m)[1]
Spillway type	Ungated overflow
Spillway capacity	112,600 cu ft/s (3,190 m3/s)[2]
Reservoir
Creates	New Melones Lake
Total capacity	2,400,000 acre feet (3,000,000 dam3)[3]
Catchment area	904 sq mi (2,340 km2)[2]
Surface area	12,500 acres (5,100 ha)[3]
Normal elevation	1,088 ft (332 m)[2]
Power station
Commission date	1979[4]
Hydraulic head	480 ft (150 m)[4]
Turbines	2x 150 MW Francis[4]
Installed capacity	300 MW[4]
Annual generation	322,596,000 KWh[5]

New Melones Dam is an earth and rock filled embankment dam on the Stanislaus River, about 5 mi (8.0 km) west of Jamestown, California in the United States. The water impounded by the 625-foot (191 m)-tall dam forms New Melones Lake, California's fourth largest reservoir,^[6] in the foothills of the Sierra Nevada east of the San Joaquin Valley. The dam serves mainly for irrigation water supply, and also provides hydropower generation, flood control and recreation benefits.

New Melones was authorized in 1944 as a unit of the Central Valley Project, a system designed to provide irrigation water to the fertile agricultural region of the Central Valley. The dam would be built by the U.S. Army Corps of Engineers (USACE), and transferred to the U.S. Bureau of Reclamation (USBR) upon completion. In 1966, work began to clear the foundations for a high dam that would replace an earlier structure built by two irrigation districts. Construction of the main embankment began in 1976, and was topped out in late 1978. Water storage in New Melones Lake commenced in 1978, and the dam's hydroelectric station produced its first power in mid-1979.

The dam was the focus of a long environmental controversy and was one of the last large dams built in California. Critics protested the flooding of a long scenic stretch of the Stanislaus River, which flowed over whitewater rapids through the deepest limestone canyon in the western United States. The protestors employed a variety of methods, some extreme, to prevent the filling of New Melones Lake until 1983, when record-setting floods filled the reservoir and overflowed the dam's emergency spillway. Because of the controversy in addition to lower-than-expected water yields from the new dam, the USBR has called it "a case study of all that can go wrong with a project."^[7]

Specifications

New Melones Dam and its reservoir comprise the independent New Melones Unit of the Central Valley Project. The dam's primary purpose is to control the runoff from 904 sq mi (2,340 km²),^[2] or about 92 percent, of the watershed of the Stanislaus River, a major tributary of the San Joaquin River.^[8] At 625 ft (191 m) high from the foundations and 1,560 ft (480 m) long, and containing 15,700,000 cu yd (12,000,000 m³) of material, New Melones is the fifth largest embankment dam in California by volume, after Oroville, San Luis, Trinity, and Don Pedro.^[8] With a crest elevation of 1,135 ft (346 m), the dam rises for 541 ft (165 m) above the streambed.^[1] Flood waters are released through an unlined spillway about a mile (1.6 km) northwest of the dam, with a capacity of 112,600 cu ft/s (3,190 m³/s).^[2] The dam also has a set of outlet works, which can release up to 8,300 cu ft/s (240 m³/s).^[2]

The impounded water behind the dam forms New Melones Lake, which at full pool of 1,088 ft (332 m) above sea level encompasses 12,500 acres (5,100 ha) of surface water^[3] and a volume of 2,400,000 acre·ft (3,000,000 dam³).^[8] About 450,000 acre·ft (560,000 dam³), 19 percent of the reservoir's capacity, is reserved for flood control.^[9] During flooding events, the dam is operated to keep flows on the Stanislaus River below 8,000 cu ft/s (230 m³/s), although this figure may be lowered depending on flow conditions in the San Joaquin River.^[9] From 1979 to 1993, the dam and reservoir prevented an estimated $128,500,000 in flood damage.^[8]

New Melones Dam also serves for water supply and electricity generation. The dam's hydroelectric power plant is located at its base on the north side of the river, and has a rated hydraulic head of 480 ft (150 m).^[4] The plant houses two 150.0 MW Francis turbines for a total capacity of 300 MW. Releases are made on a peaking basis and are also dictated by irrigation and flood control requirements below the dam.^[4][8] The plant produces about 323 million kilowatt hours annually.^[5] By controlling the flows of the Stanislaus River, the dam and reservoir also make available 200,000 to 280,000 acre·ft (250,000 to 350,000 dam³) of surplus water each year. Under contract, the dam furnishes an annual 150,000 acre·ft (190,000 dam³) to the Stockton East Water District and Central San Joaquin Water Conservation District.^[8] The increase in water supply from New Melones Dam has "translated into prosperity for the region, allowing the growth of cities including Tracy and Manteca, and irrigating high-value crops including almonds, walnuts and grapes."^[10]

Background and construction

In 1926, the Oakdale Irrigation District and South San Joaquin Irrigation District completed the original Melones Dam, a 211-foot (64 m) high concrete arch dam with a storage capacity of 112,500 acre·ft (138,800 dam³).^[11] The first proposal to expand the dam and reservoir was authorized in the Flood Control Act of 1944, which cleared the way for the implementation of a 355 ft (108 m) arch dam with a capacity of 450,000 acre·ft (560,000 dam³). The dam would generate electricity using the original 22 MW Melones hydroelectric plant, and provide flood control to 35,000 acres (14,000 ha) of farmland as well as the towns of Oakdale, Riverbank and Ripon.^[8] The irrigation districts conducted their own study later in the 1940s, determining that a larger dam capable of holding 1,100,000 acre·ft (1,400,000 dam³) would better suit their needs.^[12] The USBR first surveyed the New Melones dam site in the 1950s, hoping to incorporate a reservoir with over twice the capacity of that proposed by the irrigation districts, as part of the recently authorized Central Valley Project.^[12]

Old Melones Dam

Over ten years later, the Flood Control Act of 1962 authorized the final design of the dam – changing it from an arch to an embankment dam, increasing the size of the projected reservoir to 2,400,000 acre·ft (3,000,000 dam³) and requiring the construction of a new power plant.^[8][12] Because the dam was to serve primarily for flood control, the USACE took over construction, opening bids for contractors on October 10, 1972. Melones Contractors won the primary construction contract for approximately $110 million, while Allis-Chalmers and General Electric were paid $11.5 million to provide turbines and hydroelectric generating equipment.^[7] During reservoir clearing operations, the USACE spent about $28 million relocating roads and bridges in the future reservoir space.^[7]

Actual construction began in July 1966 with clearing of the dam and reservoir site, construction of access roads, foundation preparations and excavations for the future outlet works. A diversion tunnel to allow the river to bypass the dam site was excavated between 1966 and December 1973.^[8] Work on the main dam structure began on March 6, 1974 with the first embankment material placed in January 1976.^[7] Much of the embankment fill came from an excavation site shortly northwest of the dam, which would later serve as the dam's spillway. The embankment reached a height of 400 ft (120 m) by February 1978, and was topped out on October 28 of that year.^[7] Meanwhile, on April 1 the gates of the diversion tunnel were closed, and New Melones Lake began to rise.^[13] As the reservoir filled, work moved ahead on the power plant and generating units, which were all completed by the end of 1978. In 1980, operations of the dam and reservoir were handed to the USBR.^[7] The reservoir first reached full capacity in 1983.^[14]

Controversy

New Melones Dam was not without its controversies, and was fiercely opposed by groups such as the Sierra Club and individuals – especially river runners – who saw the Stanislaus River canyon as having greater value than a reservoir.^[7] Another cause of concern was the unique ecology of the canyon, which included endemic species such as Banksula melones, the Melones cave harvestman. The controversy raged in courts for years, culminating on May 20, 1979, as New Melones Lake was already rising. On that day, Friends of the River founder Mark Dubois hiked into the reservoir site and chained himself to a boulder, forcing the USACE to either stop filling the lake or to drown him.^[16][17]

Dubois's actions won a temporary reprieve for the river above Parrott's Ferry Bridge, as the California State Water Resources Control Board set the limit for lake level at 844 ft (257 m) above sea level, corresponding to a storage capacity of 438,000 acre·ft (540,000 dam³).^[7] However, in 1982 a record snowmelt combined with heavy rains caused the Stanislaus River to flow into the reservoir at a rate much higher than it could be released from the dam. The water level passed the state limit on January 15 and by early 1983, the water had risen so high that it crested the dam's emergency spillway. In March 1983, the state lifted its original restriction on New Melones lake level.^[7] Nevertheless, the controversy over the dam greatly strengthened the environmental movement in California, and very few new large dams have been built in the state since New Melones.^[17]

See also

• California State Water Project
• List of United States Bureau of Reclamation dams
• List of dams and reservoirs in California
• List of largest reservoirs of California
• List of power stations in California
• List of the tallest dams in the United States
• Tulloch Dam

References

Works cited

• Lowry, William Robert (2003). Dam Politics: Restoring America's Rivers. Georgetown University Press. ISBN 0-87840-390-6. 
• Palmer, Tim (1984). Stanislaus: The Struggle for a River. University of California Press. ISBN 0-52005-225-0. 

External links

Wikimedia Commons has media related to New Melones Dam.

• New Melones Dam
• New Melones Power Plant
• Post-Audit of New Melones Dam, by Kimra Dawn McAfee (Master's Thesis, May 2000)
• Station Meta Data: New Melones Dam (NML)
• U.S. Geological Survey Geographic Names Information System: (Tuolumne County)
• U.S. Geological Survey Geographic Names Information System: (Calaveras County)