Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 8882
Title: Concentration, extent, and duration of salinity intrusion into the Columbia River estuary September-October, 1977-1978
Author/Editor: Robert J. McConnell, George R. Snyder, Joseph T. Durkin, Theodore H. Blahm
Publication Year: 1979
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon

Eight 24-h surveys were conducted during September and October 1977 and 1978 to record the extent, concentration, and duration of salinity intrusions into the Columbia River estuary.  Monitoring stations were established at Tongue Point, Harrington Point, Grays Point, and in the North channel of Cathlamet Bay.  The objective was to simultaneously measure salinity during maximum (spring)1 and minimum (neap)2 tidal cycles.

Monthly neap tides produced the highest concentrations with the longest durations and farthest upstream intrusions of saline waters.  Salinities reached 30 parts per thousand (o/oo) at Tongue Point and 17 o/oo at Harrington Point.  Concentrations of salt water exceeding 11 o/oo were measured continually throughout one 24-h survey (7-8 September 1977) at Tongue and Grays Points.  The farthest upstream intrusion of salt water > 2.0 o/oo was recorded between Buoy 14 and 14A at Columbia River Mile (RM) 26.5.3

1 Tides of increased range occurring during the times of a new and full moon; these tides rise higher and fall lower than during the rest of the month.
2 Tides of decreased range occurring during time of the first and last quaters; these tides do not rise as high or fall as low as tides during the rest of the month.
3 River distances are presented in statute miles and tide elevations in feet to correspond to common usage on navigation and tide charts.