General

Under its original authorization, the Auburn-Folsom South Unit was intended to provide a new and supplemental water supply for irrigation and municipal and industrial needs and to alleviate the badly depleted groundwater conditions in the Folsom-South service area (Sacramento and San Joaquin counties south of the American River).

The unit was also intended to provide significant increases in hydropower generation, fish protection and enhancement and recreation. In combination with Folsom Dam and Reservoir and downstream facilities, the unit was designed to provide increased flood protection for much of the Sacramento area.

History

The Auburn-Folsom South Unit was authorized as an operationally and financially integrated part of the Central Valley Project (CVP) in September 1965, by Public Law 89-161. Authorized features of the Auburn-Folsom South Unit include in the following:

• Auburn multi-purpose Dam, Reservoir and Powerplant on the North Fork of the American River
• Sugar Pine Dam, Reservoir and Conveyance
• County Line Dam, Reservoir and Conveyance
• Folsom South Canal

Construction on the Auburn-Folsom South Unit was initiated in 1967. However, major construction on the Auburn Dam portion of the Auburn-Folsom South Unit was halted in 1975, to re-evaluate the design after the earthquake occurred near Oroville, California. As a result of this seismic evaluation, two new designs were proposed for consideration, an earth-fill dam and a concrete curved gravity dam. Both would be located slightly downstream from the original alignment. A feasibility design and estimate was prepared for the concrete gravity dam in 1980. Sugar Pine Dam, Reservoir, and conveyance have been completed in 1982, and ownership was transferred to the Foresthill Public Utility District in November 2003. No construction activity has been initiated on the County Line Dam and associated features. The Folsom South Canal was designed for a total of five reaches and construction of the first two reaches, approximately 27 miles, was completed in 1973. In Auburn-Folsom South Unit Report - Section 209(a) of Public Law 109-103, dated Nov. 19, 2005, authorized the Secretary of the Interior to complete a Special Report to update the analysis of costs and associated benefits of the authorized Auburn-Folsom South Unit.

Construction

The Auburn-Folsom South Unit consists of Sugar Pine Dam and Reservoir, Auburn Dam, Reservoir and Powerplant, Folsom South Canal, and County Line Dam and Reservoir.

Of the these features, only Sugar Pine Dam and Reservoir are complete, providing water for irrigation, and municipal and industrial uses in the Foresthill Divide area. Folsom South Canal, about one-third complete, provides water for municipal and industrial use in Sacramento and San Joaquin counties. The remaining unconstructed portion of about 42 miles is delayed pending reauthorization. Construction of Auburn Dam, Reservoir and Powerplant was well underway when construction was halted due to concerns about the ability of the dam to withstand a major earthquake. Construction of the County Line Dam and Reservoir, although approved, has been indefinitely delayed.

Plan

In conjunction with Folsom and Nimbus Dams and other facilities of the Central Valley Project, Auburn Reservoir would control the varying flows of the north and middle forks of the American River. Releases from the reservoir would operate Auburn Powerplant and supply the Folsom South Canal. The dam site is on the North Fork of the American River, adjacent to the city of Auburn, California. Construction of Auburn Dam, Reservoir, and Powerplant was well under way when construction was halted because of concerns about the ability of the dam to withstand a major earthquake. Construction of the dam has been delayed due to environmental and safety concerns. Construction of Auburn Dam required relocating several roads in the area and a bridge that would carry the roadway over a portion of the reservoir that would be created by the dam. Work on the bridge was completed in mid-1973, and dedication ceremonies took place on September 1, 1973.

The Auburn-Foresthill Bridge is the second highest bridge built by the Reclamation, surpassed only by the bridge at Glen Canyon. Rising 720 feet above the valley floor, it is a 2,428 foot-long, steel truss bridge with an 862 foot-long center section and two 639 foot-long approach sections. The diversion tunnel was completed in November 1972. In May 1974, work began on the foundation. On August 1, 1975, an earthquake measuring 5.7 on the Richter Scale occurred near the Oroville Dam, about 50 miles northwest of the Auburn site. Although the large earth-fill structure was not damaged, the event raised concerns about the safety of dams like the thin arch concrete dam proposed for the Auburn site. While engineers and geologists began to look into the safety concerns, work at Auburn continued. In April 1976, the Association of Engineering Geologists, Seismic Hazards Committee, issued a report stating that a moderate earthquake like the 1975 event near Oroville would cause the proposed dam at Auburn to fail. Concerns about dam safety were further heightened in June 1976, when the Teton Dam in Idaho failed. The earthquake requirements for the dam site led to a re-evaluation of the type of dam to be constructed. Alternatives being considered are rock-fill and curved concrete gravity-type dams. Reservoir capacity behind such a structure would be about 2,300,000 acre-feet. Auburn Powerplant was to be built at the downstream toe of Auburn Dam and would house five units, each with a capacity of 150,000 kilowatts.

Sugar Pine Dam, located on North Shirttail Canyon approximately 7 miles north of Foresthill, California, is an earth and rock-fill structure 205 feet high, with a crest length of 689 feet. The maximum base width from upstream toe to downstream toe is 984 feet; the total volume of material in the dam is 987,500 cubic feet. Reservoir capacity is 6,921 acre-feet with a surface area of 165 acres. The dam was completed in 1982, and the project was transferred to the Foresthill Public Utility District for operation and maintenance in 1984. During the drought years from 1987 to 1992, Sugar Pine Dam was one of the shining stars of the Central Valley Project. During each year of the drought but one, the reservoir filled and spilled, and was able to meet and exceed all obligations to its water users. Construction of the Sugar Pine Dam began in early 1979. Excavations for the foundation began in February, with work on the diversion tunnel starting in June. The tunnel was holed through on August 31. By the end of 1979, the tunnel and spillway excavations were complete, and concrete was being placed in the outlet works and spillway chute. Work on clearing the pipeline route for the eight mile-long Sugar Pine Pipeline began in October, with pipe laying operations beginning on December 12. The pipeline carries water from Sugar Pine Reservoir to the Foresthill Divide area. Sugar Pine Pipeline is a steel and iron structure eight miles long. The diameter begins at 27-inches and reduces to 24-inches. The capacity of the pipeline is 13 cubic feet per second. The pipeline was completed in 1983. County Line Dam and Reservoir was to provide water for irrigation and municipal and industrial use in the Folsom-Malby area. Although authorized for construction, the project has been delayed indefinitely. The dam, to be located on Deer Creek, about 10 miles south of Folsom Dam, would create a reservoir with a capacity of 40,000 acre-feet.

County Line Dam would be an earth-fill structure 90 feet high and 585 feet long. County Line Reservoir will operate in conjunction with pumping from Folsom Lake to provide water service in the Folsom-Malby area for municipal and industrial use. The Folsom South Canal was planned to be constructed in five reaches for a total length of 68.8 miles. Only the first two reaches have been built, a total length of 26.7 miles, and there are no current plans to construct the remaining three reaches, about 42 miles, delayed pending reauthorization. The canal originates at Nimbus Dam, on the American River, in Sacramento County, and extends southward. As originally planned, it would terminate about 20 miles southeast of the city of Stockton. This concrete-lined canal has a capacity of 3,500 cubic feet per second for the first two reaches, a total of 26.7 miles. The canal has a bottom width of 34 feet, and the maximum water depth is 17.8 feet. The maximum capacity of Reaches No. 1 and 2, is 3,500 cfs.

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Overview

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