NOAA Fisheries annually develops survival estimates of juvenile salmonids passing through dams and reservoirs on the Snake and Columbia Rivers. The estimates include passage through reservoirs and dams. Recent proposals to change spill at dams during the summer has led to concerns about effect on mortality for smolts passing through the tailrace of the dams. Estimates of direct mortality from turbines and spill are available at many projects, but we lack information on how changes in spill and turbine discharge impact tailrace conditions and how these changes may affect predation rates on fish passing the dams. This research will develop analytical model tools to understand how predation rates vary with respect to changes in hydraulic conditions in tailrace areas below these hydroelectric dams, and how operational changes in turbine, spillway and lock discharge affect predation behavior.