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USGS Water-Year Summary 2024
11276500 Tuolumne River near Hetch Hetchy, CA
LOCATION - Lat 37°56'15", long 119°47'50" referenced to North American Datum of 1927, in SW 1/4 SE 1/4 sec.17, T.1 N., R.20 E., Tuolumne County, CA, Hydrologic Unit 18040009, in Yosemite National Park, on left bank 1 mi downstream from O'Shaughnessy Dam at Hetch Hetchy, 2.5 mi downstream from Falls Creek, and 5.0 mi northeast of Mather.
DRAINAGE AREA - 457 mi².
REVISIONS HISTORY - WSP 1930: Drainage area.
SURFACE-WATER RECORDS
PERIOD OF RECORD - October 1910 to current year. Monthly discharge only for some periods, published in WSP 1315-A. Published as "at Hetch Hetchy damsite, near Sequoia" 1910-14 and as "below Hetch Hetchy damsite, near Sequoia" 1915-18.
GAGE - Water-stage recorder, crest-stage gage with concrete control since May 5, 1970. Datum of gage is 3,452.21 ft above NAVD of 1988. Prior to Jan. 1, 1915, water-stage recorder at site 1 mi upstream, at damsite, at different datum. Jan. 1, 1915, to Sept. 3, 1968, water-stage recorder, at same site and datum. Oct. 1, 1968, to May 4, 1970, nonrecording gage at site 0.5 mi upstream at different datum.
REMARKS - Flow regulated by Hetch Hetchy Reservoir (station 11275500) 0.9 mi upstream beginning in April 1923. Flow diverted upstream from station through tunnel to Robert C. Kirkwood Powerplant and Hetch Hetchy Aqueduct beginning Apr. 26, 1967. See schematic diagram of Tuolumne River Basin available from the California Water Science Center.
EXTREMES FOR PERIOD OF RECORD - Maximum discharge, 16,400 ft³/s, Jan. 3, 1997, gage height, 15.08 ft; no flow at times in 1968-70.
WATER-QUALITY RECORDS
PERIOD OF RECORD -
CONTINUOUS WATER-QUALITY DATA: WITH INTERRUPTION
WATER TEMPERATURE: Water years October 1971 to September 1972, August 1987 to current year (water years 1972, 1987-2023, daily).
CONTINUOUS WATER-QUALITY DATA: WITH INTERRUPTION
WATER TEMPERATURE: Water years October 1971 to September 1972, August 1987 to current year (water years 1972, 1987-2023, daily).
INSTRUMENTATION - Water-temperature recorder October 1971 to September 1972, and since August 1987. Aug. 13, 1987, to Feb. 2, 2009, and since Aug. 17, 2011, water-temperature recorder located 0.6 mi upstream from gaging station on left bank at road bridge. Water-temperature recorder located at gaging station from Feb. 3, 2009, to Aug. 16, 2011.
REMARKS - Water temperature can be affected by releases from O'Shaughnessy Dam.
