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USGS Water-Year Summary 2024
12177700 GORGE RESERVOIR NEAR NEWHALEM, WA
LOCATION - Lat 48°41'53", long 121°12'25" referenced to North American Datum of 1927, in NW 1/4 sec.14, T.37 N., R.12 E., Whatcom County, WA, Hydrologic Unit 17110005, Ross Lake National Recreation Area, at Gorge Dam on Skagit River, 2.4 mi upstream from Gorge powerplant at Newhalem, and at mile 96.6.
DRAINAGE AREA - 1,159 mi². includes 400 mi² in Canada.
REVISIONS HISTORY - Gage data was previously published using the 'elevation, ft above NGVD29' parameter. This was in error as the gage references the as-built datum of the dam which predates NGVD29. Beginning 12/9/2020, published data is using the 'gage height' parameter and a conversion to NAVD88 is now referenced.
SURFACE-WATER RECORDS
PERIOD OF RECORD - June 1960 to current year.
GAGE - Water-stage recorder; prior to Apr. 1, 1962, reference point on Gorge Dam or water-stage indicator in powerhouse. Datum of gage is City of Seattle Gorge High Dam as-built datum which is 6.42 ft above NAVD88 (from SCL survey of 5/2018). Prior to 2021, datum was listed as 1.792 ft below NGVD of 1929 (from Corps of Engineers' benchmark).
REMARKS - Reservoir is formed by concrete-arch and gravity dam, completed Dec. 27, 1960; storage began June 27, 1960. Usable storage, 2,115 acre-ft between elevations 865 ft, normal lower limit of operation, and 875 ft, top of gates. Lowest outlet at elevation 760 ft. No dead storage. Crest of spillway is at elevation 825 ft. Water used by City of Seattle for power development at Gorge powerplant. Capacity table furnished by City of Seattle. Figures given herein represent total contents.
EXTREMES FOR PERIOD OF RECORD - Maximum contents, 9,761 acre-ft June 1, 1982, elevation, 880.01 ft; minimum observed contents since normal low operating level was reached in Dec. 1960, 172 acre-ft Aug. 13, 1997, elevation, 781.75 ft (City of Seattle).
