Mcnary Dam Fishway Entrance Modifications to Improve Lamprey Passage

From 2005-2010, the U.S. Army Corps of Engineers (Corps), Walla Walla District evaluated adult Pacific lamprey (Entosphenus tridentatus) passage success at McNary Dam using a combination of radio telemetry and underwater optical and acoustic video (DIDSON). Evaluation results identified fishway entrances as particularly difficult passage obstacles. Upon entry, lamprey passage success improves as they migrate up the ladder.  Apropos, the Corps evaluated lamprey passage relative to lowering telescoping weir gates at night to reduce entrance velocities from 8 to 4 ft/s in 2011, as well as raising telescoping entrance weirs to create a 16” deep water attraction slot in 2012. In response to these evaluations, a prototype lamprey entrance structure was installed in the bottom of the south fishway in 2014. The prototype incorporated variable low flow velocities (4-6 ft/s) with a multi-level entrance to improve lamprey entrance efficiency and passage.

This presentation describes the methods and results of these evaluations, biological design criteria and associated limitations in the design of the prototype, and results of preliminary prototype testing in 2014.  A companion presentation describes the prototype physical hydraulic modeling and design effort.