Gatewell Exclusion Screen Evaluation at the Priest Rapids Hydroelectric Project in 2010

Gatewell exclusion screen testing was performed at Wanapum and Priest Rapids dams, of the Priest Rapids Hydroelectric Project operated by Grant County Public Utility District No. 2 on the Columbia River.   A single screen was installed at each project in a bulkhead slot on a turbine intake prior to the juvenile salmonid outmigration in the spring of 2010.  A DIDSON camera (dual frequency identification sonar) was installed to monitor interactions with the screens by all fishes moving past the screens into the turbine.   DIDSON provides high resolution “near optical” imagery of an insonified area regardless of ambient light or turbidity.  The DIDSON was installed on the far edge of the screen allowing 80% of the screen surface to be effectively imaged.  Fishes were enumerated as they passed within the insonified area near the screen and any interaction with the screen was classified by type, either contact with or impingement on the screen.  From May through July a total of eighteen days of data collection spread throughout the spring and summer salmonid migration periods were analyzed from each dam.  At Wanapum Dam 15,718 fishes were counted with 590 (3.75%) contacts with the screen and 17 (0.11%) fishes impinged.   At Priest Rapids Dam we observed 33,636 fishes with 271 (0.81%) contacts with the screen and 22 (0.14%) fishes impinged.   The degree to which any damage or injury occurs from contact with the screen is unknown, however, impingement was considered potentially more detrimental than contact alone due to the length of time involved.  We speculate that fewer fishes were counted at Wanapum Dam due to a combination of the unique characteristics of each dam combined with a large portion of the juvenile salmonids using the newly constructed surface bypass at Wanapum Dam, which diverted approximately 70% of smolts away from the powerhouse.   The fishes that passed near the screens had a generally low level of interaction with them and a very low level of impingement.   Additional results and images will be presented.