The U.S. Army Corps of Engineers owns and operates eight large lock and dams on the lower Snake and Columbia Rivers in Washington and Oregon. Each of these dams has fish collection and bypass facilities for both upstream-migrating adult fish and downstream-migrating juvenile fish, primarily several species of salmon and steelhead, but also including shad, lamprey, bull trout and other resident species.
Responding to a March 2017 U.S. District Court order, gas cap spill operations were implemented in the spring of 2018 at the eight Federal lower Columbia and Snake River dams, with the gas cap defined as the spill discharge resulting in 120 percent saturation of Total Dissolved Gasses (TDG) in a given project tailrace or 115 percent saturation in the forebay of the next downstream project. Prior to this implementation, the Corps’ Northwestern Division and Walla Walla and Portland Districts performed extensive preparation, including empirical modeling to estimate gas caps at each operating project for different ranges of river discharge, physical hydraulic modeling to develop operating configurations at each project to optimize and balance tailrace flow conditions for juvenile fish downstream egress and adult fish upstream attraction and passage, baseline bathymetric surveys of the stilling basin and immediate tailrace area of each project, and planning for monitoring the effects of this gas cap spill operation on both adult and juvenile fish. Close coordination and direct involvement with federal, state, and tribal fishery agencies and commercial navigation stakeholders in the region was maintained throughout the process.
This presentation will describe the actions taken to prepare for and implement this gas cap spill operation, with emphasis on the modeling and coordination efforts. A companion presentation will describe the preliminary biological monitoring results from the first year of operation.