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USGS Water-Year Summary 2024
11287500 Don Pedro Reservoir near La Grange, CA
LOCATION - Lat 37°42'06", long 120°25'16" referenced to North American Datum of 1927, in NE 1/4 SW 1/4 sec.03, T.3 S., R.14 E., Tuolumne County, CA, Hydrologic Unit 18040009, on left end of New Don Pedro Dam on Tuolumne River, 500 ft downstream from Mexican Gulch, and 3.4 mi northeast of La Grange.
DRAINAGE AREA - 1,534 mi².
REVISIONS HISTORY - WSP 1930: Drainage area.
SURFACE-WATER RECORDS
PERIOD OF RECORD - September 1923 to current year. Year-end contents only 1923-24, and October 1924 to September 1930 monthend contents, published in WSP 1315-A.
GAGE - Water-stage recorder. Datum of gage is NGVD of 1929 and 2.59 ft above NAVD of 1988. Prior to Feb. 1, 1941, nonrecording gage at site 1.5 mi upstream at same datum. Feb. 2, 1941, to Nov. 3, 1970, water-stage recorder at site 1.5 mi upstream at same datum. Nov. 4, 1970, to Apr. 26, 1972, nonrecording gage at same site and datum.
REMARKS - Reservoir is formed by earth-fill dam completed June 23, 1971. Storage began Nov. 3, 1970. Total capacity, based on capacity table provided by Modesto and Turlock irrigation districts, August 1970, 2,030,000 acre-ft, at elevation 830.0 ft, top of uncontrolled spillway, of which 309,000 acre-ft below elevation 600.0 ft, mutually agreed-upon minimum, is not available for release. Water passes through powerplant at dam and down Tuolumne River to La Grange Dam, 2.5 mi downstream, where it is diverted into Turlock and Modesto Canals (stations 11289500 and 11289000) for irrigation. This reservoir is operated jointly by Turlock and Modesto Irrigation Districts. Prior to June 1971, reservoir was formed by a concrete gravity-type dam completed Jan. 1, 1923, capacity, 290,400 acre-ft. Records, excluding extremes, represent total contents at 2400 hours. See schematic diagram of Tuolumne River Basin available from the California Water Science Center.
EXTREMES FOR PERIOD OF RECORD - Maximum contents, 2,044,000 acre-ft, Jan. 2, 1997, elevation, 831.11 ft; minimum, 29,200 acre-ft, Sept. 1-3, 5, 1934, minimum elevation, 475.0 ft, Sept. 1, 2, 1934. Minimum since reservoir first filled, 302,600 acre-ft, Oct. 14, 15, 1977, elevation, 598.2 ft.
