Into submerged orifices. — Some fish arriving below a 

 dam do not readily find entrances to fishways. Most dams 

 on the Columbia River have a multientrance channel built 

 into the powerhouse below the dam. Migrating fish enter 

 the channel through submerged poi'ts or orifices and are 

 guided by currents to the fish ladders (fig. 27). 



CROSS SECTION OF POWERHOUSE 



Submerged O'ifrce 

 Entfonce 



Fo'eboy 



''lo„ ^^~^~^-<^. ■■ '• ■■/ / /• -I 



D'Od Tube ^<-^^.^ r /;j 



FIGURE 27.— ABOVE. Diagrammatic sketch of a typical power- 

 house showing a submerged orifice entrance to the fishway. 

 RIGHT. Some of the experimental orifices used in the lab- 

 oratory at Bonneville Dam. 



Our studies indicated that the relative attraction of a 

 fishway entrance with a submerged orifice may be influenced 

 by flow and light, relative brightness of the area, and the 

 size of the orifice. Light appeared to be particularly influ- 

 ential. Fish adapted to light were reluctant to enter a dark 

 orifice. If given a choice, a larger proportion entered the 

 illuminated orifice regardless of flow or brightness of the 

 surrounding area. 



Many of the collection systems at dam powerhouses are 

 so poorly illuminated that conditions possibly could be im- 

 proved by lighting. 



Tracing Movements of Salmon 



Although much has been learned about passing fish over 

 dams, some runs of salmon and steelhead trout slowly con- 

 tinue to decline; occasionally runs suff'er drastic losses. 



Unexplained losses of adult salmon and steelhead trout 

 between certain dams have been as high as 46 percent and 

 average 20 percent each year. Field studies in 1967-68 at- 

 tempted to discover where and how delays and losses of fish 

 occurred. 



— 22 — 



