problem is, of course, to remove the immobi- 

 lized fish from the field before death results. 

 The water velocities within the field offer the 

 only practicable solution to this problem. 



Three test installations of this type of 

 weir have been made on the West Coast. In 

 two of these at Entiat and Quilcene, the water 

 velocities and pattern of stream flow within the 

 electrical field have proved adequate . In the 

 third, in the Little White Salmon River, 1 per- 

 cent of the diverted run was killed within the 

 electrical field. This mortality was caused by 

 an inadequate water velocity along the stream 

 bottom . 



At the Little White Salmon weir site the 

 river was constricted into a narrow channel. 

 The surface flow approximated 3 feet per sec- 

 ond. The bottom, however, was strewn with 

 large boulders. In this bottom area there was 

 no perceptible current flow. Fish which be- 

 came immobilized within the field dropped to 

 the bottom and died. At the time of installation 

 the condition was obscured by the fast surface 

 flow. 



Two alternatives are available to correct 

 such a condition: the first entails relocating 

 the weir at a more suitable site where bottom 

 contours are more favorable and the second is 

 to alter the bottom contours at the selected site 

 by filling the area with rock to smooth the bot- 

 tom and reduce the cross sectional area. In 

 this manner both a higher and more uniform 

 water velocity within the electrical field may be 

 attained and mortality eliminated. 



The water flow within an alternating cur- 

 rent field should have a minimum velocity of 

 3 feet per second to provide an effective barrier. 

 The maximum velocity is limited by the strength 

 of the installation. In figure 4 the Entiat weir 

 is shown operating at velocities of 10 feet per 

 second. The flow pattern within the electrical 

 field is, also, of particular significance . Ed- 

 dies contained within the field must be avoided. 

 An immobilized fish caught in an eddy within the 

 field will be killed. Vertical stratification, such 

 as existed at the Little White Salmon weir site, 

 must be eliminated. The stream flow and water 

 pattern requirements within an electrical field 

 must be fulfilled if the barrier is to operate 



efficiently. Obviously these requirements are 

 as important as the characteristics of the elec- 

 trical field itself. 



The characteristics of an alternating 

 current electrical field as created by the Entiat - 

 type installation present certain problems which 

 must be considered if the weir is to prove an 

 effective barrier and mortality avoided. Two 

 types of voltage gradient exist within this type 

 of weir. The first gradient develops parallel 

 to the electrode line and the second between the 

 electrodes and the ground line. Both of these 

 gradients are of significance in the efficient 

 operation of the weir . 



According to McMillan (1929) equlpoten- 

 tial voltages develop in concentric rings around 

 the individual electrodes. Adjacent to the elec- 

 trodes, these voltages are high, in excess of 2 

 volts per inch, and drop rapidly as the midpoint 

 between electrodes is approached. At a 3 -foot 

 spacing between electrodes in weirs of the Entiat 

 type, the volts per inch at the midpoint between 

 electrodes is less than 0.2 volts and is insufficient 

 to immobilize salmon rapidly. As the lines of 

 electrical current flow converge, however, these 

 abrupt gradients decrease until, with 3 -foot elec- 

 trode spacings, a uniform voltage is present 

 approximately 4 feet downstream from the elec- 

 trodes. This voltage represents the minimum 

 barrier strength of the weir; although higher 

 voltages exist adjacent to the electrodes, much 

 lower voltages exist in closely surrounding areas. 

 The minimum barrier strength required with a 

 minimum water velocity of 3 feet per second is 

 0.5 volt per inch. 



The second significant voltage gradient 

 develops between the minimum voltage barrier 

 and the ground line and at right angles to the 

 electrode line. The highest uniform voltages 

 per inch are encountered at the voltage barrier 

 and gradually decrease as the ground line is 

 approached. Beyond the ground line the voltage 

 gradient drops abruptly. The length and strength 

 of the field may be varied by the distance between 

 the electrodes and the ground line and the distance 

 between electrodes. With the electrode spacing 

 constant, the greater the distance between the 

 electrode line and the ground line the weaker the 

 field strength will be, but conversely, the longer 

 the effective field. With the distance between 



