New Don Pedro Dam

Coordinates: 37°41′58″N 120°25′15″W / 37.69944°N 120.42083°W / 37.69944; -120.42083
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The New Don Pedro Dam
KWh (2001–2012)[4]

New Don Pedro Dam, often known simply as Don Pedro Dam, is an earthen embankment dam across the Tuolumne River, about 2 miles (3.2 km) northeast of La Grange, in Tuolumne County, California. The dam was completed in 1971, after four years of construction, to replace the 1924 concrete-arch Don Pedro Dam.

The dam serves mainly for irrigation water storage,

Sierra Nevada
.

The New Don Pedro Dam is owned and operated by the

artificial lake in California.[6]

The original dam was named for the old mining town of Don Pedros Bar on the Tuolumne River, which in turn takes its name from prospector

Pierre "Don Pedro" Sainsevain.[7]

Background

Don Pedro Dam is named after Don Pedro Sainsevain.

Shortly after their formation in 1887, the MID and TID acquired water rights to the Tuolumne River to secure a water supply for their combined 1,000-square-mile (2,600 km2) service area in the

megawatt (MW) hydroelectric plant, later expanded to 37.5 MW,[11] delivered its first power in October 1923.[12]

Expanding Don Pedro or constructing a new dam altogether was first seriously considered in the 1940s because the existing dam could only store a year's supply of water for valley farmers, with no guarantee that a multiyear drought could be weathered.

U.S. Bureau of Reclamation made tentative studies for a high dam on the Tuolumne River as part of its Central Valley Project, though it later dropped the plans in favor of other sites.[13]

Construction

The first Don Pedro Dam, later to be submerged under the new reservoir

In 1961, an overwhelming majority of voters in the TID and MID service areas and San Francisco approved bond issues to finance the construction of a new dam.

king salmon in the Tuolumne put a temporary stop to the project.[15] In fact, it was not until that year that the Federal Power Commission (now Federal Energy Regulatory Commission) licensed the irrigation districts to go ahead on New Don Pedro.[14]

The $49.7 million primary construction contract for the dam was awarded to Guy F. Atkinson Company on August 22, 1967. When he first saw the dam site, chief engineer John Goodier was reported to have said "[it'd be a] tough nut to crack".[16] Clearing the dam site began immediately afterwards, in addition to the construction of access roads and a camp for construction workers. Construction of the dam's service spillway began a week later on August 29. On September 22, 1967, work began on the diversion tunnel that would allow the river to bypass the construction site. The 3,415-foot (1,041 m) tunnel was fully excavated by March 13 of the following year and lined with reinforced concrete by August. On September 7, a 40-foot (12 m) cofferdam was constructed and the diversion tunnel began to carry the flow of the Tuolumne. As the dam site dried out, the foundations were excavated down to bedrock; cracks in the rock were injected with so-called "dental concrete" to stabilize the foundation.[17]

Construction of the embankment began on September 16, 1968 using the hydraulic fill method. The dam's massive concrete emergency spillway was completed on January 19, 1969. However, severe flooding on January 26 destroyed the cofferdam and all of the construction site's bridges, putting work a month behind schedule.[18] Cleanup proceeded at a rapid pace and placing of impervious material for the dam's core commenced on February 27.[17] For the next fifteen months, a fleet of massive 125-ton (113 t) dump trucks delivered an almost constant stream of dirt and rock to the site, and the dam wall rose at an average rate of one and a half feet (0.46 m) per day. The workforce peaked at 500 men in mid-1969 and on December 10, the service spillway was completed. On May 28, 1970, the embankment was finally topped out with the last of over 250,000 truckloads of material.[17]

After the clearing of over 7,000 acres (2,800 ha) of the future reservoir site and the relocation of several roads that ran through it, the diversion tunnel was closed and water began to rise behind New Don Pedro. The rising lake submerged Old Don Pedro Dam on April 12, 1970 and inundated the

Gold Rush town of Jacksonville by June. The powerhouse and penstocks were completed by August 1970, after lengthy delays and setbacks due to the sheer scale of the generators, pipes and gates used in their construction. Some of the individual components were so heavy that a truck delivering one of the penstock sections sank up to its trailer bed in the road, and another was crushed when the driver braked, inadvertently snapping the chains that held the load in place.[17]

"We have harnessed a great river to serve man. There is a vision, imagination, sense of beauty about it. Environment and development will never meet, but a delicate balance of the two has been achieved at Don Pedro Dam."

–Joseph Alioto, mayor of San Francisco, at 1971 New Don Pedro Dam dedication[17]

The total cost of the New Don Pedro Dam project, including site preparations, reservoir clearing and road relocations, was $115,679,000.[19] The dam was formally dedicated on May 22, 1971 to a crowd of over 3,000 people. Among the dedication ceremonies were a speech by San Francisco mayor Joseph Alioto and a beef barbecue hosted by TID.[20]

Design and usage

Rising 585 feet (178 m) above its foundations and 560 feet (170 m) above the Tuolumne River,

radial gates, has a capacity of 172,000 cubic feet per second (4,900 m3/s), and finally the emergency spillway, a 995-foot (303 m) long concrete overflow structure, can discharge more than 300,000 cubic feet per second (8,500 m3/s).[17]

Don Pedro Reservoir is seen at near full capacity in 2005

The hydroelectric plant at the base of the dam has four generators capable of producing 203 MW combined. The TID's share is 139 MW or 68.47%, while MID receives 64 MW or 31.53%.

kilowatt hours (KWh) of electricity each year, equal to an average output of 70.6 MW.[23] The cities of Modesto and Turlock receive a large share of their power supplies from New Don Pedro Dam.[16]

Don Pedro Reservoir has a capacity of 2,030,000 acre-feet (2.50 km3), of which 340,000 acre-feet (0.42 km3) is reserved for flood control and 1,381,000 acre-feet (1.703 km3) is available for irrigation, municipal water supply, and hydroelectric generation. The flood control reservation is one of the smallest among major California reservoirs because it allows for more water to be stored for power generation, but this has often resulted in inadequate flood protection such as in 1997 when the dam released more than 50,000 cubic feet per second (1,400 m3/s) – almost six times the capacity of downstream levees.[22] The bottom 309,000 acre-feet (0.381 km3) is considered dead storage, or the lowest point at which water can be released to generate power.[1] At an elevation of 804 feet (245 m) (service spillway crest), the reservoir is 25 miles (40 km) long, and has an area of 12,960 acres (5,240 ha)[2] with 160 miles (260 km) of shoreline.[1] The maximum elevation of the reservoir at the crest of the emergency spillway is 830 feet (250 m) above sea level.[22]

During construction of the dam, it was anticipated that the large size and scenic location of the reservoir, coupled with its proximity to urban centers, would make it a large tourist draw. A $40,000 plan was put forth to develop the reservoir for recreational activities. This entailed the construction of campsites, picnic areas, boat ramps, a landing strip, and hiking trails, including on 14 of the 33 islands in the lake.[24] Don Pedro has become a popular summer destination in Central California, attracting 360,000–400,000 visitors each year.[1]

Future development

In 1923, the same year that Old Don Pedro was completed, the City of San Francisco finished construction of

Hetch Hetchy Aqueduct and there would be a net loss of hydroelectric generation from O'Shaughnessy.[27] Of note is that San Francisco is already entitled to 453,000 acre-feet (0.559 km3) of the water stored in Don Pedro, although this allocation is overruled by the senior water rights of the irrigation districts during dry years.[28]

TID is currently[

peaking power demands without releasing extra water at New Don Pedro Dam.[29] The proposed Red Mountain Bar Project would involve building a 465-foot (142 m) high dam across a canyon adjacent to Lake Don Pedro, creating a reservoir with a capacity of 25,000 to 42,000 acre-feet (0.031 to 0.052 km3). Water would be pumped into this new reservoir using power generated at New Don Pedro Dam during periods of low electricity demand, while during high demand water would be released through a penstock to an 880 MW generating facility.[30] As of September 2011, poor economic conditions had put the project "on hold indefinitely".[31]

See also

References

  1. ^ a b c d e f g h i "Don Pedro Reservoir" (PDF). Turlock Irrigation District. Don Pedro Recreation Agency. Retrieved March 26, 2012.[permanent dead link]
  2. ^ a b c d "Don Pedro Reservoir (DNP)". California Data Exchange Center. California Department of Water Resources. Retrieved March 26, 2012.
  3. ^ "Don Pedro Dam". UC Davis. Archived from the original on January 30, 2015. Retrieved January 30, 2015.
  4. ^ "California Hydroelectric Statistics & Data". California Energy Commission. Archived from the original on February 26, 2018. Retrieved April 26, 2018.
  5. ^ "Dam, Hydropower and Reservoir Statistics". United States Society on Dams. Archived from the original on March 25, 2012. Retrieved March 28, 2012.
  6. ^ "Alphabetical List of California Dams (Over 40,000 acre feet)". Civil and Environmental Engineering. University of California Davis. Archived from the original on February 5, 2012. Retrieved March 28, 2012.
  7. ^ "Don Pedro – There Really Was One, But He Was A Frenchman!". Don Pedro Recreation Agency. February 20, 1972. Archived from the original on March 6, 2012. Retrieved March 26, 2012.
  8. ^ "Background". Don Pedro Project Relicensing. Archived from the original on March 4, 2016. Retrieved March 26, 2012.
  9. ^ a b c Cantatore, Alex (February 1, 2011). "TID prepares for Don Pedro relicensing process". Turlock Journal. Retrieved March 26, 2012.
  10. ^ Beanfield, R. McC. (1922). "Novel Construction Features on 279-Ft. Don Pedro". Engineering News-Record. 88 (22): 896–900.
  11. ^ a b c Cummerow, David (February 16, 1966). "New Dam By '70 Appears Possible". The Modesto Bee.
  12. ^ Baggese, p. 67
  13. ^ William De Roos, p. 197
  14. ^ a b "Don Pedro: A newsletter about the relicensing of the Don Pedro Project" (PDF). Don Pedro Project Relicensing. Archived from the original (PDF) on March 3, 2016. Retrieved March 27, 2012.
  15. ^ Cummerow, David (February 17, 1966). "Growing Storm Wrecked '66 Target Date – Fish Issue Cost Five Years In Planning New Don Pedro Dam". The Modesto Bee.
  16. ^ a b Dalquist, Josiah (January 17, 2011). "Dam project was a tough nut to crack". Foothill Express. Archived from the original on March 3, 2016. Retrieved March 27, 2012.
  17. ^ a b c d e f Barnes, Dwight H. "Chapter 17: The Dirt Begins to Fly" (PDF). Greening of Paradise Valley – The First 100 Years of the Modesto Irrigation District. Modesto Irrigation District. Archived from the original (PDF) on November 25, 2010. Retrieved March 26, 2012.
  18. ^ ICOLD, p. 100
  19. ^ "New Don Pedro Dam and Powerhouse". Greening of Paradise Valley. Archived from the original on February 18, 2013. Retrieved March 27, 2012.
  20. ^ "Aqueduct Spans Northern California" (PDF). San Francisco Water and Power. Delta REvision. Retrieved March 27, 2012.
  21. ^ "Don Pedro Main". National Performance of Dams Program. Stanford University. Retrieved March 27, 2012.[permanent dead link]
  22. ^ a b c Virk, Suhkwant; Hinkey, Josh. "Don Pedro Dam". University of California Davis. Archived from the original on June 10, 2010. Retrieved March 28, 2012.
  23. ^ "3.9 Energy Resources" (PDF). Meeting Flow Objectives for the San Joaquin River Agreement 1999–2010: Environmental Impact Statement and Environmental Impact Report. San Joaquin River Group Authority. January 28, 1999. Retrieved March 26, 2012.
  24. ^ Gray, Thorne (March 19, 1967). "New Don Pedro Reservoir Will Offer Fun Facilities". The Modesto Bee.
  25. ^ Null, Sarah E. (December 2003). "Re-Assembling Hetch Hetchy: Water Supply Implications of Removing O'Shaughnessy Dam". University of California Davis.
  26. ^ Brower, David (1990). "Restoring Hetch Hetchy". For Earth's Sake: The Life And Times of David Brower. Sierra Club. Retrieved March 28, 2012.
  27. ^ "Where will San Francisco's water be stored?". Restore Hetch Hetchy. Archived from the original on March 22, 2012. Retrieved March 28, 2012.
  28. ^ Righter, p. 188
  29. ^ Petersen, Amy (October 2008). "Red Mountain Bar Pumped Storage Project" (PDF). Turlock Irrigation District. Northwest Power and Conservation Council. Retrieved March 28, 2012.
  30. ^ "Red Mountain Bar Pumped Storage Project" (PDF). Turlock Irrigation District. Stanford University. September 2009. Retrieved March 28, 2012.
  31. ^ Caskey, Chris (September 9, 2011). "Red Mountain storage dam project on hold indefinitely". The Union Democrat. Retrieved March 28, 2012.

Works cited

External links
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