(U) Install light channel iron crosspiece, 10 feet long, at 

 appropriate height on each dual tower to establish anchor for horizon- 

 tal cables providing alignment and direct support of the electrode 

 array. 



In stream locations where maximum flood depths do not exceed 

 5 feet, water velocities do exceed 1.0 f.p.s., and stream bed materials 

 are firm, an array consisting of a single row of suspended electrodes 

 and a horizontal, submerged electrode may be substituted for the 

 multiple-row installation. Details of a recommended design for this 

 type of array may be derived from the plans for an electrical barrier 

 presented in Figure 19. Should field observations indicate that this 

 array is causing an appreciable mortality among migrant fishes, it may 

 prove expedient to shift the horizontal, submerged electrode to a posi- 

 tion on the upstream side of the row of suspended electrodes. 



In those sea lamprey spawning streams that have no fish runs 

 of importance, it is recommended that simple, electrical barriers be in- 

 stalled. Such streams will, as a rule, be small and the array consisting 

 of a single row of suspended elements and a horizontal, submerged elec- 

 trode will be adequate for most locations. A design for an electrical 

 barrier utilizing this type of array is presented in Figure 19. In very 

 small tributaries, an electrical barrier may be effected by installing 

 only two horizontal, submerged electrodes placed parallel to each other 

 on the stream bed. A suggested design for such an installation is pre- 

 sented in a sketch in Figure 20. However, until the working limits of 

 this very simple device are determined, it is not recommended that it be 

 installed in streams having maximum flood depths greater than 2 feet at 

 the point of installation. 



All recommended designs and suggested modifications are based 

 on the utilization of sources of Jpower providing 110 VAC for application 

 to the arrays. In all cases, a minimum voltage gradient of 1.0 volt per 

 inch between specified electrode elements (as described in previous sec- 

 tions) should be established. Although appreciably higher than the min- 

 imum of 0.75 volt per inch required to block sea lampreys, this arbitrary 

 minimum provides a suitable margin of protection against seasonal changes 

 in water conductivity, losses of electrical field strength due to inad- 

 vertant grounding of distal ends of hanging electrodes, erratic field 

 patterns created by displacement of electrodes, and other minor variables 

 causing local or general weakening of the electrical fields. 



Electromechanical weir-traps and the approaches to these traps 

 should be thoroughly explored with the voltmeter probe to determine if 

 these areas are adequately "cold w from an electrical standpoint. The 

 maximum voltage gradient permissable in these areas which will not repel 

 or stun fishes is in the order of 0.2 volt per inch. Excessive gradients 

 can usually be reduced by increasing the size of the shunt screens (i.e., 



U7 



