electrodes and the ground line constant, the 

 closer the electrodes are spaced the stronger 

 the electrical field will be, the closer the mini- 

 mum voltage barrier will be to the electrodes, 

 and the more abrupt will be the voltage gradient 

 between the electrode and ground lines. Table 

 1 demonstrates the effect of three combinations 

 of electrode and ground line spacings on the 

 voltage gradient. The average voltage per inch 

 was derived from a minimum of four readings 

 across the field and represents the minimum 

 voltage, since the readings were taken at points 

 equidistant between electrodes. Although the 

 conductivity of both the water and the stream 

 bottom may vary between locations it is possible 

 to secure the minimum voltage requirement by 

 varying either the electrode or ground line 

 spacing. 



In this type of installation the length of 

 the field is as important as the minimum barrier 

 voltage because the fish are not immobilized 

 immediately by low voltages. McMillan (1928) 

 found that voltages between 0.19 and 0.25 volts 

 per inch were required to paralyze adult chinook 

 salmon in 1 minute. A field of this strength 

 would have to be well in excess of 15 feet in 

 length in order to immobilize a fish attempting 

 to move through it. Andrew, Johnson, and 

 Kersey (1956) found that 2.5 volts per inch were 

 required in a 4 -foot alternating current field to 

 provide a positive barrier to adult sockeye and 

 pink salmon when the water velocity varied from 

 1.8 to 2.5 feet per second. At the Entiat weir 

 when stream velocities varied from 3 to 5 feet 

 per second neither sockeye nor chinook salmon 

 were observed to oenetrate the electrical field 



* Location of ground line 



