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USGS Water-Year Summary 2025
12085500 LA GRANDE RESERVOIR AT LA GRANDE, WA
LOCATION - Lat 46°49'23", long 122°18'13" referenced to North American Datum of 1927, in SW 1/4 SE 1/4 sec.33, T.16 N., R.4 E., Thurston County, WA, Hydrologic Unit 17110015, at left end of gate control structure, 1.1 mi southeast of La Grande, 1.7 mi downstream from Alder Dam, and at mile 42.5.
DRAINAGE AREA - 289 mi².
SURFACE-WATER RECORDS
PERIOD OF RECORD - January 1945 to current year. January 1945 to September 1951 included in combined adjustment to monthly flow of Nisqually River at La Grande. Month-end contents January 1945 to September 1950, published in WSP 1316.
GAGE - Water-stage recorder. Datum of gage is 7.61 ft below NGVD of 1929 (levels by City of Tacoma) and is 4.15 ft below NAVD of 1988 (NCAT conversion by USGS, April 24, 2024). Prior to June 12, 1947, month-end gage heights furnished by City of Tacoma from temporary gages in pool upstream from dam.
REMARKS - Reservoir is formed by concrete gravity dam completed in 1944; storage began in February 1945. Useable storage, 1,053 acre-ft between gage heights 910 ft, minimum practical head, and 935 ft, normal reservoir level. Dead storage below gage height 910 ft, 1,629 acre-ft. Figures given herein represent total contents. Water used by Tacoma Public Utilities for power generation.
EXTREMES FOR PERIOD OF RECORD - Maximum contents, 2,760 acre-ft, May 14, 1950, gage height, 936.4 ft; minimum contents observed since reservoir first filled, 1,370 acre-ft, Aug. 24, 1956, gage height, 900.0 ft.
