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Water-Year Summary for Site 12085000

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  • Water-Year Summary reports summarize a year of hydrologic data in a printer-friendly format.
  • For water years 2014 onward, choose a water year and parameter and an on-demand Water-Year Summary report will be generated.
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Available Parameters
00054 Reservoir storage(Obs.)  
00065 Gage height(Obs.)  

Water year 2023: 2022-10-01 to 2023-09-30

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USGS Water-Year Summary 2023
LOCATION - Lat 46°48'09", long 122°18'37" referenced to North American Datum of 1927, in SE 1/4 NW 1/4 sec.09, T.15 N., R.4 E., Thurston County, WA, Hydrologic Unit 17110015, near left end of Alder Dam on Nisqually River, 1.0 mi west of Alder, 1.7 mi upstream from La Grande Dam, 4.6 mi upstream from Mashel River, and at mile 44.2.
DRAINAGE AREA - 286 mi².
PERIOD OF RECORD - November 1944 to current year. 
GAGE - Water-stage recorder. Datum of gage is 7.61 ft below NGVD of 1929 (levels by Tacoma Public Utilities). Prior to July 8, 1946, nonrecording gage at same site and datum.
REMARKS - Reservoir is formed by concrete-arch dam; storage began Nov. 7, 1944; dam completed in 1945. Usable capacity, 161,457 acre-ft (based on 1985 survey) between gage heights 1,114 ft, lower limit of operating range, and 1,207 ft, top of spillway gates. Unused storage below gage height 1,114 ft, 52,110 acre-ft. Crest of spillway is at gage height 1,177 ft. Figures given herein represent total contents. Capacity table, dated 1985, furnished by Tacoma Public Utilities. Water is used by City of Tacoma for power generation. Chemical analyses December 1973 to September 1983 (samples were taken near the dam).
EXTREMES FOR PERIOD OF RECORD - Maximum contents, 233,848 acre-ft, Dec. 4, 1975, gage height, 1,207.68 ft; minimum contents since reservoir first filled, 70,430 acre-ft, Oct. 26, 2018, gage height, 1,134.23 ft.