Figure 23. — Ice Harbor design fishway in operation. 



Transitions in spiitial relationships, water veloc- 

 ities, and particularly light affect the movement 

 of fish into, through, and out of the laboratory. 

 The effect of an abrupt change in conditions is 

 usually hesitancy and dela_y. 



The ability of all species of salmonids to nego- 

 tiate overfalls up to '.i feet was frequently demon- 

 strated in the laboratory (fig. 20). However, it 

 was generally observed that the fish would swim 

 easily over a 1-foot overfall but that it usually had 

 to resort to jumping over higher overfalls. The 

 additional energy expended, the delays and the 

 increased probabilitj- of minor injuries that would 

 make the fish more susceptible to disease suggests 

 that overfalls greater than 1 foot are undesirable 

 for standard fisliwaj"s. 



Research directed toward the passage problems 

 of downstream migrants was largely postponed 

 because of the priority given to adult passage 

 problems. 



Exploratory experiments conducted to test tiie 

 reactions of chinook fingerlings to an overfall, 

 an orifice, and a siphon are illustrated in figure 



21. A 3.5-inch orifice at a depth of 7 feet was 

 far more effective (80 percent) in attracting and 

 collecting fingerlings than a 7-inch overfall of 

 comparable width. The siphon with an intake 

 18 inches below the surface was also more ef- 

 fective than the overfall. 



CURRENT RESEARCH 



Experiments now in progress at the laboratory 

 are centered around a full-scale model (figs. 22 

 and 23) of the 1-on-lO-slope fishway designed for 

 the north shore of Ice Harbor Dam, now under 

 construction on the lower Snake River, a major 

 tributary of the Columbia. Pattern and rate of 

 fish movement, space utilization, and capacity- 

 potential are being examined in the 6-pool section 

 of the fishway. 



The experiments this year demonstrate a special 

 function of the Fisheries-Engineering Research 

 liaboratory — that of providing the means by 

 which new fish passage devices and new features 

 of fishway design may be biologically tested and 

 proven to have merit before being permanently 

 cast in concrete. 



15 



