11275500  HETCH HETCHY RESERVOIR AT HETCH HETCHY, CA

LOCATION.--Lat 37°56'52", long 119°47'13", in NW 1/4 NW 1/4 sec.16, T.1 N., R.20 E., Tuolumne County, Hydrologic
   Unit 18040009, Yosemite National Park, near center of O'Shaughnessy Dam on Tuolumne River at Hetch Hetchy,
   1.5 mi downstream from Falls Creek.
DRAINAGE AREA.--455 mi2.
PERIOD OF RECORD.--May 1923 to current year.  Prior to October 1930 monthend contents published in WSP 1315-A.
REVISED RECORDS.--WSP 1930:  Drainage area.
GAGE.--Water-stage recorder installed March 1995.  Datum of gage is 1.84 ft above sea level.  Prior to Oct. 1,
   1927, nonrecording gage at same site and datum.  Oct. 1, 1927, to July 9, 1972, water-stage recorder at same
   site and datum.  Prior to October 1974, datum published as at mean sea level.
REMARKS.--Reservoir is formed by concrete gravity-type dam, completed to crest gage height 3,726.5 ft in 1923 and
   raised to 3,812.0 ft in 1937.  Storage began Apr. 6, 1923.  Ten-foot drum gates were installed on spillway in
   1949.  Capacity, 360,400 acre-ft between gage heights 3,512.0 ft, bottom outlet, and 3,806.0 ft, top of drum-
   type spillway gates.  Water is diverted from reservoir through tunnel to Robert C. Kirkwood Powerplant 15 mi
   downstream.  Flow is diverted from powerplant tailrace in a closed conduit through Hetch Hetchy Aqueduct to
   Moccasin Powerplant with flows in excess of aqueduct capacity being spilled to the river.  At Moccasin Creek
   Diversion Dam, water re-enters Hetch Hetchy Aqueduct and flows into Crystal Springs Reservoir, which supplies
   city of San Francisco.  Surplus water is spilled into Don Pedro Reservoir (station 11287500) at Red Mountain
   Bar.  Flow downriver is for State Department of Fish and Game and Raker Act requirements.  Hetch Hetchy
   Reservoir is the main storage unit of Hetch Hetchy water-supply system for San Francisco.  See schematic
   diagram of Tuolumne River basin.  Records, including extremes, represent contents at 2400 hours.
EXTREMES (AT 0800) FOR PERIOD OF RECORD.--Maximum contents, 369,100 acre-ft, Dec. 3, 1950, gage height,
   3,810.4 ft; no contents at times in 1929-31.
EXTREMES FOR CURRENT YEAR.--Maximum contents, 363,700 acre-ft, June 19, 20, gage height, 3,807.7 ft; minimum,
   238,300 acre-ft, Apr. 6, gage height, 3,739.67 ft.

                        Capacity table (gage height, in feet, and contents, in acre-feet)
           (Based on table provided by San Francisco Public Utilities Commission, dated May 20, 1971)

         3,512       0     3,530    3,300     3,600    57,400     3,680   146,200     3,760     273,700
         3,513      51     3,540    8,700     3,620    76,500     3,700   175,000     3,780     310,400
         3,515     154     3,560   22,900     3,640    97,000     3,720   206,000     3,800     348,600
         3,520     410     3,580   39,500     3,660   119,900     3,740   238,900     3,810.4   369,100


                    RESERVOIR STORAGE (ACRE-FEET), WATER YEAR OCTOBER 1995 TO SEPTEMBER 1996
                                        DAILY OBSERVATION AT 2400 HOURS

DAY       OCT      NOV      DEC      JAN      FEB      MAR      APR      MAY      JUN      JUL      AUG      SEP

  1    340000   315700   297700  e292400   281000   269500   242400   281700   316500   360500   355300   338600
  2    339300   314800   297100  e292200   278800   267700   242100   289000   322300   361700   355000   337700
  3    338500   314100   296500   291900   276600   266200   241200   295200   329200  e362500   354700   336600
  4    337800   313500   296000   291600   278700   265700   240100   300000   334500  e362500   354200   336000
  5    337100   313200   295400   291200   285700   264700   239000   304900   337800  e361700   353700   334900
  6    336400   312600   294700   291100   287600   263300   238300   309800   341500  e361500   353100   334000
  7    335700   312000   294200   290900   287800   261800   238400   313400   346300   361400   352700   333200
  8    335000   311400   293700   290800   287500   260500   239400   314000   350500   361400   352100   332500
  9    334100   310700   293100   290800   287100   259500   240900   312200   352800   361400   351700   331400
 10    333400   310200   292500   290600   286400   259200   242000   311600   353500   361200   351300   330400

 11    332500   309600   292700   290400   285500   258000   242700   313000   353800   361200   350800   329300
 12    331700   309000  e296400   290100   284400   258000   243200   316700   355700  e361900   350300   328300
 13    331100   308500  e296400   290000   283300   256100   243100   321600   360100  e362100   349900   327600
 14    330200   307900  e296600   289800   283100   254800   243300   325600   362200  e361900   349500   326700
 15    329400   307300  e296300   289800   282700   253400   244200   333300  e363100   361200   349000   325900
 16    328700   306700  e295500   291100   282800   252200   246400   347000  e362900   360400   348700   324900
 17    327900   306100  e295000  e291800   282100   251400   247500   338700  e362900   359200   348400   324200
 18    327200   305600  e294200   292600   281000   251100   248100   329600  e363500   358100   348100   323400
 19    326400   304900  e294200   293100   283600   251200  e247900   324000  e363700   357600   347600   322500
 20    325500   304400  e294200   293200   283900   251600  e247400   320500  e363700   357000   346900   321600

 21    324700   303800  e294900   293600   283400   251900  e245900   317100  e363100   356700   346300   320800
 22    324100   303100  e293700   293500   282400   252200  e245200   313200  e362700   356100   345800   319800
 23    323100   302600  e293300   293200   281100   251700  e245200   310800  e362500   356200   345000   318800
 24    322200   302000   292500   292900   279800   250700  e246800   308500   362300   356300   344400   317800
 25    321200   301300   292100   292700   278600   249500  e249900   306300   362100   356400   343700   316900
 26    320300   300800   291800   291700   276900   248300  e256100   305000   361500   356400   343000   316100
 27    319500   300200   291500   290200   275200   247000  e260600   305200   360300   356300   342500   315300
 28    318800   299600   291600   289000   273300   246400  e264800   305700   359200   356200   341700   314500
 29    318300   299000   291600   287000   271400   245100   267800   307400   358700   356100   340900   313900
 30    317400   298400   291900   285000      ---   243900   274400   309700   359200   356000   340100   312800
 31    316600      ---   292400   283000      ---   242700      ---   312600      ---   355700   339300      ---

MAX    340000   315700   297700   293600   287800   269500   274400   347000   363700   362500   355300   338600
MIN    316600   298400   291500   283000   271400   242700   238300   281700   316500   355700   339300   312800
 a    3783.29  3773.58  3770.28  3765.16  3758.72  3742.22  3760.41  3781.18  3805.41  3803.64  3795.21  3781.29
 b     -24600   -18200    -6000    -9400   -11600   -28700   +31700   +38200   +46600    -3500   -16400   -26500

CAL YR 1995  b  +95600
WTR YR 1996  b  -28400

  e Estimated.
  a Gage height, in feet, at end of month.
  b Change in contents, in acre-feet.