Walla Walla River Basin Fish Screen Evaluations; Nursery Bridge Fishway and Garden City/Lowden II Sites, 2005-2006 Progress Report.

Abstract

SummaryResults of the Garden City/Lowden evaluations indicate the site performs well at varying river levels and canal flows. Approach velocities did not exceed 0.4 feet per second (fps) at any time. Sweep velocities increased toward the fish ladder in March but not in June. The air-burst mechanism appears to keep large debris off the screens, although it does not prevent algae and periphyton from growing on the screen face, especially near the bottom of the screens.At Nursery Bridge, results indicate all the approach velocities were below 0.4 fps under the moderate river levels and operational conditions encountered on March 7, 2006. Sweep did not consistently increase toward the fish ladder, but the site generally met the criteria for safe passage of juvenile salmonids. Modifications to the louvers seem to allow more control over the amount of water moving through the screens. We will measure approach velocities when river levels are higher to determine whether the louver modifications can help correct excessive approach velocities under a range of river levels and auxiliary water supply flows.iii