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New Melones Unit Project
Non-interactive photo of New Melones dam
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General Description

The East Side Division and the construction of the New Melones Dam and Powerplant is one of the more controversial chapters in the history of the Central Valley Project. Developing the division brought the need for water and flood control into direct conflict with concerns over damage to cultural resources and the environment. The battle over construction of New Melones Dam was a signal that the end of the era of large dam construction had come. The controversy focused on the loss of a popular stretch of recreational white water, inundation of archeological sites, and flooding of the West`s deepest limestone canyon. Controversy over the project lasted over a decade before the decision to proceed and provide irrigation water, flood control, and power generation.

The New Melones Dam and Powerplant are on the Stanislaus River, about 60 miles upstream from its confluence with the San Joaquin River and 40 miles east of Stockton. The river forms the boundary between Calaveras and Tuolumne Counties, and drains an area of about 980 square miles on the western slope of the Sierra Nevada Mountains in east-central California. The Stanislaus River Basin has three major tributaries, the North, South, and Middle Forks; and the annual average flow is almost 1,000,000 acre-feet. The climate is semiarid, with hot, dry summers and cool, wet winters.

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Facility Descriptions

New Melones Dam and Lake

 New Melones Dam is located about 0.75 mile downstream from the original Melones Dam, built by the Oakdale and South San Joaquin Irrigation Districts in 1926. The original dam, a 183-foot concrete arch structure, is now submerged under the reservoir.

The new dam, an earth and rockfill structure, stands 625 feet above streambed, has a crest length of 1,560 feet, and has a total embankment volume of 16 million cubic yards of material. New Melones Dam is California's second largest earthfill dam, containing 15,700,000  cubic yards of material. The reservoir, New Melones Lake, has a capacity of 2.4 million acre-feet at a gross pool elevation of 1,088.0 ft, a water surface area of 12,500 acres, and 100 miles of shoreline.

Initial construction of New Melones Dam began in July 1966. This work consisted of building access and haul roads; constructing the low-level intake structure for the outlet works; constructing the administration building, visitor overlook, and parking lot; clearing the dam site; and excavating and grouting the foundation. Construction of the diversion tunnel began in 1966 and was completed in December 1973.  Construction of the main dam began on March 6, 1974, with embankment placing operations beginning in January 1976.  The dam embankment was "topped out" on October 28, 1978, and all work on the embankment was completed in November. Initial filling of the reservoir occurred in 1983.

The outlet  works consist of a 3,774 foot long, 23-foot diameter, concrete lined, multipurpose tunnel and two 6-foot diameter steel conduits for emergency releases. The two conduits are embedded in the concrete lining of the multipurpose tunnel, and flows through the conduits are controlled by two 72-inch ring follower gates and two 66-inch fixed-cone valves. Releases for flood control and irrigation are made  through a 13-foot-diameter branch of the multipurpose tunnel that branches into two 8-foot-diameter pipes. Flows are controlled by 96-inch ring follower gates and 78-inch  fixed-cone gates. Flows into the outlet works are controlled by a 13-foot by 27-foot  sliding gate located at the intake structure. The outlet works have a capacity of 8,300 cubic feet per second (cfs).

The spillway has an uncontrolled concrete crest and an unlined channel that was excavated through solid rock about 1.5 miles northwest of the dam. The spillway cut is 5,945 feet long and 200 feet wide, with a capacity 112,600 cfs.  Material excavated from the spillway went into the dam embankment. New Melones  Lake has a capacity of 2,400,000 acre-feet and a surface area of 12,500 acres with the water level at 1,088 feet above sea level. The shoreline is over 100 miles long.

New Melones Lake is an artificial lake in the central Sierra Nevada foothills of California. It is a reservoir behind the New Melones Dam on the Stanislaus River between the cities of Angels Camp and Sonora. The reservoir has a capacity of 2.4 million acre-feet (3.0 km³) with a surface area of 50.58 km². When it is full it has a shoreline of approximately 100 miles (160 km).s

New Melones Powerplant

The New Melones Powerplant contains two generators, each rated at 150,000 kilowatts (kW). It is located on the north bank, immediately downstream from the dam. The dependable generating capacity is about 279 megawatts, producing about 455 million kilowatt-hours of energy annually. This energy is equivalent to the annual electrical requirements of some 72,000 households.

Water is supplied to the power units by two, 17-foot-diameter, concrete-lined tunnels that branch from the multipurpose outlet tunnel. Flows into the power turbines are controlled by two, 174-inch butterfly valves. A 55-foot-diameter, 620-foot-tall surge protection shaft protects the penstock tubes and control valves from water hammer damage.

The powerplant consists of two vertical shaft, synchronous, 3-phase generators with a combined rating of 300,000 kW. The generators were manufactured by General Electric were commissioned in 1979. The generators are rated at 166,667 KVA at 0.90 power factor, 171.4 rpm, 13.8 kV, 60 hertz. The turbines are Francis type manufactured by Allis Chalmers and have a rated head of 460 feet.

The powerplant was completed and the turbines and generators installed by the end of 1978. Testing of the generating units was completed in June 1979.


The New Melones Dam was originally designed for flood control and has provided significant flood control benefits. Through 1993, the dam and lake prevented a cumulative total of $128,500,000 in flood damage

Reclamation is developing a flexible operating plan for New Melones Dam and Reservoir that establishes how available water supplies will be managed within and outside of the Stanislaus River Basin.

New Melones Reservoir on the Stanislaus River is currently operating under an `Interim Operating Agreement.` This agreement was completed in 1996 with significant input from stakeholder interests. The Interim Agreement was not developed to cover drought conditions because the stakeholders could not reach agreement on how to manage the facility during periods of extended drought.

Reclamation is conducting investigations to develop and evaluate alternative operating scenarios and will start developing an Environmental Impact Statement/Environmental Impact Report under the National Environmental Policy Act and California Environmental Quality Act in 2001.

Water Availability

It is now clear that water availability for the New Melones Project is significantly different from what had been expected. When New Melones was studied, estimates of the water available from the project used historical data on annual flows and data pertaining to preexisting claims to water in the Stanislaus River Basin. The model constructed for the study used data from the years 1922 through 1978. Under this model, the amount of water predicted to be available from the project, approximately 200,000 acre-feet, justified its construction. When data for the years 1979 through 1992 were factored into the model, Reclamation found that the previous estimates of drought and demand were off by a significant amount. (California experienced a severe drought beginning in 1987 and lasting through 1992, and demands for releases for water quality improvement were higher than anticipated.)

Original estimates anticipated that approximately 200,000 acre-feet would be available after pre-existing obligations were met. As a result of those estimates, contracts were negotiated with the Stockton East Water District and the Central San Joaquin Water Conservation District for up to 155,000 acre-feet per year. But during the drought of 1987 to 1992, preexisting obligations were not always met, and no water was available to service those contracts. As a result, the Stockton East Water District has filed suit against Reclamation seeking a judgment forcing Reclamation to meet the obligations of their contract. In 1994, Reclamation had to purchase 50,000 acre-feet of water from the Tri-Dam Project at a cost of $50.00 per acre-foot to meet the release requirements for the fall salmon run.

Temperature Controls for Downstream Fish

When the lake lowers, the old dam, now submerged, prevents cold water at the bottom of the lake from reaching the outlet works of the new dam. Thus, temperatures are too high for the fish downstream from the dam. The situation becomes most critical when the amount of water in the lake drops below 350,000 acre-feet, about the point where the layer of cold water above the old dam is exhausted.

Maintaining a minimum water level above 350,000 acre-feet is difficult when the inflows are not great enough to increase storage while meeting downstream water obligations. When the water level is around 400,000 acre-feet, power operations are suspended to make low level releases. This solution is effective until the layer of cold water above the old dam runs out. Suspending power operations reduces revenues from the project. The estimated loss from suspended power operations during the fall of 1994 was over $200,000.

Central Valley Project Improvement Act Requirements

The Central Valley Project Improvement Act (CVPIA) in 1992 changed water usage priorities. Environmental, water, and wildlife enhancement priorities moved to a level equal to or ahead of other water use priorities. As a result, less water is available to meet the obligations.

Flood Control Requirements

The 2.4 million acre-feet gross storage capacity of New Melones Lake includes a flood control reservation of 450,000 acre-feet. Under flood control conditions, release operations are designed not to exceed a flow of 8,000 cfs (channel capacity) in the Lower Stanislaus River from Goodwin Dam downstream to the San Joaquin River. Unit operations provide releases for downstream fishery requirements, water quality, water rights, and a water supply yield estimated at about 180,000 acre-feet to meet present and projected agricultural and municipal and industrial water needs in the service area.

Operating Agencies

The New Melones Unit was officially transferred to Reclamation in November 1979 for integrated operation as a unit of the Central Valley Project.

The Oakdale and South San Joaquin Irrigation Districts own and operate the downstream Goodwin Diversion Dam, which diverts Stanislaus River water into the district`s canals. The two districts also own and operate the Tri-Dam Project, which consists of Donnells Dam, Reservoir, and Powerplant; Beardsley Dam, Reservoir, and Powerplant, on the Middle Fork Stanislaus River upstream from New Melones Dam; and Tulloch Dam, Reservoir, and Powerplant, located immediately downstream from New Melones Dam. Tulloch Reservoir provides afterbay storage for reregulating power releases from New Melones Powerplant under contractual arrangements between the Bureau and the two districts.

On the North Fork Stanislaus River, storage developments consist of Pacific Gas and Electric (PG & E) Company`s Lake Alpine, Utica Reservoir, Union Reservoir, and Spicer Reservoir. Also owned and operated by PG & E are Relief Reservoir; Stanislaus Powerplant; Spring Gap Powerplant, on the Middle Fork; and Strawberry and Lyons Reservoirs on the South Fork.

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Development of the Stanislaus River Basin began during the gold rush of the late 1840s. The Stanislaus River Basin and the region served by water from the basin were well developed and settled prior to construction of New Melones Dam. Development water companies diverted water for use by miners. In the 1890s, utility companies began generating hydroelectric power on the river, much of which they sent outside the area. The early 1900s saw development of several irrigation districts to serve local farmers. In 1926, the Oakdale and South San Joaquin Irrigation Districts built the Melones Dam and Powerplant. The peak of construction by irrigation districts came in the 1950s with construction of the Tri-Dam Project, which consists of the Donnells and Beardsley Dams on the upper Stanislaus River, Tulloch Dam on the lower Stanislaus River, and the enlargement of Goodwin Dam, also on the lower river.



The Flood Control Act of December, 1944, authorized construction of a dam to replace Melones Dam. The U.S. Army Corps of Engineers was to build and operate this dam to help alleviate serious flooding problems along the Stanislaus and Lower San Joaquin Rivers.

In the Flood Control Act of October, 1962, the Congress reauthorized and expanded the project (P.L. 87-874) to a multipurpose unit to be built by the Corps and operated by the Secretary of Interior as part of the Central Valley Project, thus creating the New Melones Unit. The multipurpose objectives of the unit include flood control, irrigation, municipal and industrial water supply, power generation, fishery enhancement, water quality improvement, and recreation. Irrigation and storage facilities have been developed on the Stanislaus River both upstream and downstream from New Melones Dam.

While the 1944 authorization called for construction of a 355-foot-high concrete arch dam with a capacity of 450,000 acre-feet and the continued use of the existing powerplant, the reauthorization of the project in 1962 changed the design to a 625-foot-high earth and rockfill dam and required construction of a new powerplant.

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Flood Control

The primary function of New Melones Dam and Lake is flood control. Of the 2,400,000 acre-feet capacity, 450,000 acre-feet is reserved for flood control purposes

Water Supply

The remaining capacity is used for a number of purposes including the satisfaction of preexisting water rights, fisheries enhancement, water quality improvement, and electrical generation.


New Melones website


The New Melones powerplant provides power for the equivalent of 72,000 households. The table below shows gross power generation in fiscal year 1998

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Last updated: May 26, 2010