New Melones Dam - Background and Construction

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). 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. Area irrigation interests 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. 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.

Over ten years later, in 1962, 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. 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 about $110 million, while Allis-Chalmers and General Electric were paid a combined $11.5 million to provide turbines and hydroelectric generating equipment. During reservoir clearing operations, the USACE spent about $28 million relocating roads and bridges in the future reservoir space.

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. Work on the main dam structure began on March 6, 1974 with the first embankment material placed in January 1976. Much of the embankment fill came from an excavation site shortly northwest of the dam, which would later serve as the dam's spillway. During the height of construction in the summer, the total workforce could reach 800, while averaging between 500–600 in the winter months. The embankment reached a height of 400 ft (120 m) by February 1978, and was topped out on October 28 of that year. Meanwhile, on April 1 the gates of the diversion tunnel and New Melones Lake began to rise. 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. The reservoir first reached full capacity in 1983.