Walla Walla River Basin Fish Screen Evaluations, 2001 : Burlingame and Little Walla Walla Sites.

The Pacific Northwest National Laboratory (PNNL) evaluated 2 newly constructed fish screen sites in the Walla Walla River Basin during the spring of 2001. The fish screens facilities at the Little Walla Walla River in Milton-Freewater, Oregon and at Burlingame west of Walla Walla, Washington were examined to determine if they were being effectively operated and maintained to provide for safe fish passage. Data were collected to determine if velocities in front of the screens and in the bypasses met current National Marine Fisheries Service (NMFS) criteria to promote safe and timely fish passage and whether bypass outfall conditions allowed fish to safely return to the river. Due to a calibration problem with the instrument used to measure water velocities during the spring evaluations, we re-evaluated the water velocities at both sites after the canals discharges were increased in the fall. Based on the results of our studies in 2001, we concluded: Burlingame site--The rotary-drum screen design appeared to be efficiently protecting juvenile fish from entrainment, impingement, and migration delay in May and June. However, sediment and debris accumulations in the screen forebay could result in screen seal wear (due to silt) and may increase mortality due to predation in the screen forebay (due to woody debris accumulations along the screen face). All approach velocities were below the NMFS criteria of 0.4 feet per second in November. Sweep velocities were appreciably higher than approach velocities, however sweep velocities did not increase toward the bypass. Bypass velocity was greater than sweep velocities. Little Walla Walla--The flat-plate screen design appeared to be efficiently protecting juvenile fish from entrainment, impingement, and migration delay in May and June. All approach velocities were below the NMFS criteria of 0.4 feet per second in November. Sweep velocities were substantially higher than approach velocities and increased toward the bypass. Bypass velocity was greater than sweep velocities. The automated cleaning brushes at the Little Walla Walla site generally functioned properly. However, there was a small (6 to 12 in.) band along the length of the facility at the bottom of the screen that was not being cleaned effectively by the brush. In addition, the cable that drives the cleaning brush was showing signs of wear (cracks and frays) and should be replaced