Water Temperature Modulation at Lower Granite Dam to Improve Adult Summer Chinook and Sockeye Salmon Passage Conversion

The U.S. Army Corps of Engineers, Walla Walla District has evaluated Adult Pacific salmon passage through Snake River dams since 1961 using window counts and radio telemetry, and more recent installations of Passive Integrated Transponder (PIT) antennas.  Evaluation results identified passage delays and fallout behaviors typically in August when water temperatures exceeding 20degC result in temperature differentials from 2-5degC between the fishway entrances and exits, particularly at Lower Granite Dam where forebay gradations of temperature develop with depth due to hypolimnetic releases from Dworshak Dam. Temperature related passage obstacle durations and extremes have been amplified in recent years 2013 and 2014 due to lower inflow induced water temperature threshold profiles beginning in June inducing significant effects on passage survival for the ESA-listed sockeye escapement.   During July 2013 and 2014, the Corps implemented emergency pumping of cooler forebay thermocline waters at 30 feet deep into the Lower Granite fishway in an effort to successfully pass the summer-run stocks, collect data for design of deeper sourced water intakes, and ability to operate an adult trap previously closed during the high temperature differential regimes of past July-Augusts. Temperature modulation structures will be constructed prior to June 2016 for post-monitoring of passage improvement.