field can be established over a conductive 

 bottom . The principal disadvantage is a 

 greater power consumption. Because of a 

 large and unexplained variation in power con- 

 sumption from stream to stream, it is difficult 

 to determine the actual correlation between 

 power consumption and the ratio of bottom re- 

 sistivity to water resistivity. 



During the early part of the operational 

 season, when water temperature was low and 

 the volume of runoff water was large, the 

 water resistance was sufficiently high that a 

 ratio (bottom to water resistance) of 1 : 8 was 

 recorded for Harlow Creek. A drop in this 

 ratio to 1 : 1 .5 by mid-July indicated that the 

 conductivity for that particular stream had in- 

 creased considerably. To be sure, a change 

 in the ratio of water resistivity to bottom re- 

 sistivity does not provide an exact means of 

 determining the change in conductivity of the 

 water. A rise in power consumption on the Au 

 Train River, which had a controlled water 

 level, indicates a more than twofold increase 

 in the water conductivity of that stream. 



Comparisons of water conductivity between 

 streams were checked by measuring dissolved 

 solids in parts per million with a Nalcometer . 

 The water resistance was determined by using 

 the same equipment and essentially the same 

 procedure as that used for finding the ratio of 

 bottom resistivity to water resistivity. The 

 values obtained by this method of measuring 

 water resistance are relative and can be used 

 only for comparisons. Inasmuch as other 

 factors influence water conductivity, the amount 

 of dissolved solids alone, as measured by the 

 Nalcometer, did not give an accurate indication 

 of water resistance; however, a negative cor- 

 relation between dissolved solids and measured 

 resistance for the water in the 10 streams was 

 evident . 



The effects of increases in the conductivity 

 of the water cannot be discussed in detail, be- 

 cause we were unable to obtain sufficient data 

 to judge, fcfce importance of ail the influencing 



factors. Changes of water level, especially, 

 conceal the effects of changes in conductivity 

 by decreasing or increasing the immersed 

 area of the electrodes. In general, the in- 

 crease in water conductivity is disadvanl i- 

 geous. The most obvious difficulties are as 

 follows: 



1 . Increased water conductivity increases 

 power consumption, with resulting gi eater 

 costs. 



2. Increased conductivity increases the in- 

 tensity of the electrical field in most 

 streams. This increase is especially great 

 where there is no loss of area of submerged 

 electrodes, as in streams that have the 

 bottom -type electrodes. Low water, com- 

 paratively large electrode area, and in- 

 creased water conductivity combine to give 

 an intense electrical field that may in turn 

 cause excessive mortality or injury. 



3 . Perhaps the most important result of 

 increased water conductivity is the increase 

 in the size of the electrical field . A fringe 

 field may gradually extend downstream until 

 it envelops the trap entrances . Although 

 the isolation of the trap entrances offered a 

 problem in some streams at the time of 

 installation, the problem became more 

 serious as the season progressed. This 

 problem has been minimized by extending a 

 bare copper conductor from the trap wings 

 to a stake in the stream bed below the down- 

 stream edge of the fringe field. Generally, 

 the angle of extension from the end of the 

 wings has been greater than the angle of 

 opening formed by the wings . In shallow 

 water (up to 18 inches), one such conductor 

 has been sufficient . In water deeper than 



18 inches, two have been installed- -one a 

 few inches from the bottom and the second 

 near the surface. At two installations, 

 small -diameter rods, clamped to the end 

 of the wings, served the same purpose 

 satisfactorily. 



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