ELECTRIC FISH SCREEN 115 



When an electric screen is installed in such a way that the field has the correct 

 relation to both the opening protected and the direction of water flow, as explained 

 above, fish entering the electric field of the screen are almost compelled to enter paral- 

 lel with the lines of current flow and at right angles to the equipotential surfaces. 

 This is the position of maximimi discomfort and hence is most effective in discouraging 

 further progress toward the protected opening. 



Heretofore no attention has been given to the relation of the electric field to the 

 protected opening and to the direction of stream flow. As far as is known, all of the 

 electric "stops" have been installed, either with a plate (or metal screen) on each side 

 of the protected opening (these plates being of opposite polarity), or several electrodes 

 have been used in one or several rows across the opening, the electrodes in the rows 

 alternating in polarity. Both of these schemes, it will be observed, produce an 

 electric field in which the lines of current flow are parallel with the plane of the opening 

 and the equipotential surfaces are perpendicular to this plane. This arrangement, 

 as shown above, is the most ineffective that it is possible to make, and if any success 

 has been attained at all by this arrangement it augurs well for electric screens installed 

 with the field in the proper relation to the opening and water flow. 



ELECTRIC SCREENS SHOULD BE USED AS DEFLECTORS, NOT STOPS 



Another serious error that has been made in the installation of electric "stops" 

 has been the attempt to use them as impenetrable barriers in canals, sometimes miles 

 from the intake at the supply stream. This, in general, is not good practice even 

 if successful in stopping the fish, especially for young salmon fingerlings that are 

 impelled b}' instinct to migrate downstream toward the ocean. They may be held 

 for months by such a trap and may never return upstream to the intake and main 

 stream leading to the ocean. A short interruption of the potential supply on an 

 electric screen so installed would allow fish to escape past the screen, making success- 

 ful screening action for months of no avail. It is recommended that electric screens, 

 when used, be installed as defiectors, by -passing fish aioimd the openings to artificial 

 waterways dangerous to their weU-being, always keeping the fish, as far as possible, 

 in the natural stream channels. 



LAST FISH-SCREEN TEST AT BONNEVILLE 



Following the fish-screen experiments in the concrete pool, which have been 

 described, it was decided to make an electric-screen test with more fish and under as 

 nearly as practical natm-al stream conditions. After an examination of the ponds 

 and waterways at the Bonneville hatchery it was decided that ponds Nos. 12, 15, and 

 16, with their interconnecting waterways, oflfered the best available location for the 

 fifth and last electric-screen test made during this investigation. A map is included 

 in this report (fig. 11), showing the arrangement of these ponds, the location of the 

 electric screen, and the quantities of water flowing in the various interconnecting chan- 

 nels. The arrangement shown by the map was chosen because the application of the 

 by-pass or deflector principle of using the electric screen could be apphed readily. 

 The water flowing through pond No. 12 into pond No. 15 and finally discharging into 

 pond No. 16 represents the natural stream channel, and the flow from pond No. 12 

 through the west wateiway into pond No. 16 repiesents the artificial waterway 



