Don Pedro Dam
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| Don Pedro Dam | |
| Official name | New Don Pedro Dam |
|---|---|
| Impounds | Tuolumne River |
| Maintained by | Turlock Irrigation District and Modesto Irrigation District |
| Height | 585 feet(178 m) |
| Width (at base) | 2,800 feet(853 m) |
| Construction began | September of 1967 |
| Opening date | 1971 |
Don Pedro Dam may refer to either the Old Don Pedro Dam completed in 1923, or the much larger New Don Pedro Dam that was completed in 1971. These dams were built across the Tuolumne River and created Lake Don Pedro in the foothills of the Sierra Nevada mountain range in California.
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[edit] New Don Pedro Dam
The New Don Pedro Dam is an earth and rock fill dam at that is 585 feet high (178 m), 2,800 feet wide (853 m), and 1,900 feet thick (579 m) at the base. The dam contains 16,750,000 cubic yards (12,800,000 m³) of material, much of which came from gold dredge tailings in the Tuolumne River bed downstream near La Grange. Construction was started in September of 1967, the dam was topped out on May 28, 1970, and the dam was dedicated on May 22, 1971. While the Turlock Irrigation District (TID) operates the powerhouse at the dam's base, the Modesto Irrigation District (MID) owns 31.54% of the plant and so is entitled to about 63 megawatts of the 203 MW produced by the four generators.
Behind San Pedro Dam is Lake Don Pedro, also called Don Pedro Reservoir, which holds up to 2 million acre-feet of water, making it the 6th largest body of water in California. Water leaving the dam's powerhouse flows about 2.5 miles (4 km) downstream to the La Grange Dam where about 885,000 acre-feet of water is released into two canals. About 575,000 acre-feet goes through TID's canal to Turlock Lake and another 310,000 acre-feet goes through MID's canal to Modesto Lake. Nearly all of this water irrigates crops in the Turlock and Modesto Irrigation Districts. Another 230,000 acre-feet goes to San Francisco's Hetch Hetchy Water and Power. And, finally, about 780,000 acre-feet of water is delivered to the Tuolumne River channel to maintain flows in the 52 miles (84 km) of the Lower Tuolumne River through its confluence with the San Joaquin River and then into the Sacramento-San Joaquin Delta.
[edit] Old Don Pedro Dam
The original Don Pedro Dam, since 1971 also known as the Old Don Pedro Dam, was a solid concrete gravity dam that was 283 feet high (86 m), 1,000 feet wide (305 m), 16 feet thick (5 m) at the crest, and 170 feet thick (52 m) at the base. It was completed in 1923 at where the Tuolumne River had carved a narrow gorge with walls of solid rock about a mile (2 km) below Don Pedro Bar. The reservoir created by this dam contained 290,400 acre-feet (0.358 km³) of water when full, 14.3% of today's capacity. A 15 kilowatt power plant was part of the dam's original design, and two more 7500 watt generators were added in 1926 for 30 kilowatts total, just 0.015% of today's capacity. The old dam still exists about 1.5 miles (2.5 km) upstream from the new 1971 dam, and since the old dam topped out at just 580 feet (177 m) above sea level it is now under some 250 feet (76 m) of water when the new reservoir is full. An article on the construction of the old dam ("The First Don Pedro") is available on the MID web site.
[edit] References
- Turlock Irrigation District
- Modesto Irrigation District
- SFPUC: Hetch Hetchy Water and Power
- USGS Hydrologic Data
- "Lessons from Hetch Hetchy" by Richard W. Amero
- UC Davis Civil Engineering Class Project
