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USGS Water-Year Summary 2024
12436500 COLUMBIA RIVER AT GRAND COULEE DAM, WA
LOCATION - Lat 47°57'56", long 118°58'54" referenced to North American Datum of 1927, in SW 1/4 SE 1/4 sec.36, T.29 N., R.30 E., Okanogan County, WA, Hydrologic Unit 17020005, in pier 3 on west side of bridge on State Highway 155, 3,200 ft downstream from Grand Coulee Dam, 14.2 mi upstream from Nespelem River, and at mile 596.3.
DRAINAGE AREA - 74,700 mi².
REVISIONS HISTORY - WSP 1286: 1942, 1947. WSP 1933: Drainage area. Daily mean discharges for the period July 1, 1923 to Dec. 7, 2022 were revised on July 3, 2023, based on changes to reported dates of values as previous data was reported as 1 day in advance.
SURFACE-WATER RECORDS
PERIOD OF RECORD - April 1913 to June 1923 (monthly discharge only), July to December 1923, January 1924 to May 1928 (monthly discharge only), June 1928 to current year. Published as "at Grand Coulee near Nespelem" prior to 1936 and as "at Grand Coulee" 1936-42.
GAGE - Daily discharge determined from flow through turbines plus spillway flow when present. Datum of gage is NGVD of 1929, adjustment of 1937 (Bureau of Reclamation datum). June 27 to Dec. 31, 1923, June 12, 1928, to Mar. 31, 1931, nonrecording gage at site 0.5 mi upstream at datum 2.4 ft lower. Apr. 1, 1931, to Dec. 31, 1935, water-stage recorder 850 ft downstream at present datum. Jan. 1, 1936, to June 11, 1955, water-stage recorder at present site and datum. June 12, 1955, to July 18, 1988, water-stage recorder at present site and datum with auxiliary water-stage recorder 5.3 mi downstream at datum 1.42 ft lower.
COOPERATION - Discharge records provided by Bureau of Reclamation at Grand Coulee Dam through the Corps of Engineers, Northwestern Division, Reservoir Control Center.
REMARKS - Flow is regulated by numerous reservoirs. Feeder Canal diversion (station 12435500) for Columbia Basin project is used to irrigate approximately 600,000 acres in the United States. An additional 66,500 acres in Canada are irrigated by other diversions.
EXTREMES OUTSIDE PERIOD OF RECORD - Flood in June 1894 reached a discharge of 725,000 ft³/s, estimated.
EXTREMES FOR PERIOD OF RECORD - Maximum discharge, 637,800 ft³/s, June 12, 1948, elevation, 987.90 ft; minimum discharge, 14,900 ft³/s, Dec. 17, 1956, elevation, 934.37 ft; minimum daily discharge, 15,300 ft³/s, Feb. 1, 1937.
