FiQTTBE 3. — Screen support and velocity control structure at entrance to water-bypass channel. Screen is 

 raised for cleaning. Several concrete stoplogs are stacked in lower right foreground. 



the panels. By installing various numbers of these 

 plywood panels and adjusting the stoplogs in the 

 velocity control structure at the entrance to the 

 water-bypass channel, we could divert water to 

 regulate the flow. At the slowest velocity tested — 

 0.2 m.p.s. — ^the flow was about 7.4 cm.s.; at 0.5 

 m.p.s. it was 22.2 cm.s.; and at 0.8 m.p.s., 37.1 

 cm.s. The three test velocities were average veloci- 

 ties and were maintained by routine cleaning of 

 the screens. Actual water velocities varied about 

 ±0.06 m.p.s. from the desired test velocities. 



ELECTRODE ARRAY AND ELECTRICAL 

 CONDITIONS 



The angle of the electrode array to the water- 

 flow and the electrical conditions of the array were 

 held constant during the entire experiment. The 

 array consisted of three rows of vertically sus- 

 pended electrodes forming a 30° V (fig. 5). Be- 



cause the electrode array trap was constructed 

 nearer the right bank, looking downstream, and 

 both legs of the arra}' extended upstream at about 

 a 15° angle to the flow, the legs were not exactly 

 the same length. The left leg was 45.7 m. long, and 

 the right leg 30.5 m. The electrodes were supported 

 on the surface by a wooden framework and on the 

 bottom by wooden dowels. One dowel extended 

 from the bottom of each electrode and was driven 

 into the sandy canal bottom about 10 cm. These 

 dowels helped to keep the electrodes vertical at the 

 higher water velocities and also insulated them 

 from the canal bottom. The electrodes were 3-m. 

 lengths of steel pipe with an outside diameter of 

 5.1 cm. The distance between the rows of electrodes 

 in each leg of the array was 1.2 m. from the up- 

 stream row to the middle row and 0.6 m. from the 

 middle to the downstream row. Spacing between 

 the electrodes was 0.6 m. (fig. 6) . 



310 



U.S. FISH AND WILDLIFE SERVICE 



