Twenty-one flow reversals of 5 hr or longer 

 were recorded. Few reversals of 60 min or long- 

 er were recorded during river discharge above 

 8,495 m-'sec"' (300,000 cfs), regardless of the 

 height of the tide. This relation is illustrated 

 in Figure 1, where average monthly discharge 

 is compared to the frequency of flow reversal. 



The lowest high tide at which reversal was 

 recorded (90 min) was 1.5 m (4.9 ft), at 3,936 

 m^sec-i (139,000 cfs). The highest high tide 

 at which a reversal was recorded (155 min) was 

 3.0 m (9.9 ft) at 6,173 m^sec-^ (218,000 cfs). 

 Two 3-m (10-ft) tides occurred during the study 

 period at 7,759 and 7,985 m^sec"' (274,000 and 

 282,000 cfs) without producing a reversal of 

 60 min or longer. The longest period of reversal 

 was 5% hr at a tide height of 2.7 m (8.9 ft) and 

 5,550 m^sec"^ (196,000 cfs) which occurred 

 8 March 1970. 



A regression analysis was made for each tide 

 level to estimate the critical discharge below 

 which a flow reversal of 60 min or greater could 

 be expected. Discharges that allowed flow re- 

 versals at 1.5-, 1.8-, 2.1-, 2.4-, and 2.7-m (5-, 6-, 

 7-, 8-, and 9-ft) tides were 4,530; 5,720; 5,861; 

 6,852; and 8,636 m^sec"' (160,000; 202,000; 

 207,000; 242,000; and 305,000 cfs; Figure 2). 

 The rate of discharge from the river and tidal 



10.0- 



5.0 



g 2.5|- 



I 

 o 



Estimated disctiorge below i 

 floa reversals ^60 "tin occi 



\ 



5,720 



rtljch 



5,861 



8,636 



6^2 



4,530 



Ronge of flow for 

 meosured flow 

 reversals > 60 min 



2— — 120— -^329- -^406— 



^ Frequency of high tides In 

 ^study period 

 -^ 386— — 98— — 2 



1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 32 (ml 



7 8 9 



HEIGHT OF TIDE 



10 



(ft) 



Figure 2. — Graphs showing range of flow of the Colum- 

 bia River for various tidal heights at Astoria, Oreg. 

 The number within each bar is the estimated discharge 

 below which flow reversals of 60 min or longer occur 

 at Prescott, Oreg., for a given tidal height. The number 

 below each bar gives the frequency of occurrence of the 

 tide height for the study period. 



height appear to be independent variables while 

 flow reversal is the dependent variable in the 

 analysis. 



Discussion 



During the time interval examined, reversal 

 of direction of current (^ 60 min) at Prescott 

 occurred every month except June 1968 and 

 April and May 1969. It is important to discover 

 that the reversals in flow are frequent as previ- 

 ous work in this area only indicated that they 

 could occur at very low river discharges. Be- 

 cause of the frequent occurrence of flow rever- 

 sals in the region of the lower Columbia River 

 near Prescott, the regulation of waste discharges 

 in this area should receive special attention as 

 these reversals in flow tend to produce pockets 

 of high concentration of wastes in the river 

 system when the waste discharges are constant 

 in time (Clark and Snyder, 1969). 



Acknowledgment 



We gratefully acknowledge the helpful sug- 

 gestions of A. C. Duxbury, Department of Ocean- 

 ography, University of Washington, in prepar- 

 ing the manuscript. 



Literature Cited 



Clark, S. M., and G. R. Snyder. 



1969. Timing and extent of a flow reversal in the 

 lower Columbia River. Limnol. Oceanogr. 14:960- 

 965. 

 Snyder, G. R., T. H. Blahm, and R. J. McConnell. 

 1971. Floating laboratory for study of aquatic or- 

 ganisms and their environment. U.S. Dep. Com- 

 mer., Natl. Mar. Fish. Serv., Circ. 356, 16 p. 



George R. Snyder 



Northwest Fisheries Center 



National Marine Fisheries Service, NO A A 



2725 Montlake Boulevard East 



Seattle, WA 98102 



Robert J. McConnell 



Northwest Fisheries Center 



Biological Field Station 



National Marine Fisheries Service, NO A A 



P.O. Box 1051 



Longview, WA 98632 



314 



