Relative survival of juvenile salmon passing through the spillway of The Dalles Dam, 1997-2000

High rates of spill are presumed to increase passage survival forjuvenile salmonid migrants because passage survival through spillways at Columbia and Snake River dams is generally higher than through turbines. However, two conditions at The Dalles Dam may decrease spill passage survival under high spill conditions: 1) a short stilling basin and shallow tailrace result in severe turbulence and lateral currents that may cause physical injury to juvenile salmon; and 2) a large proportion of spilled water moves through shallows and islands downstream, where salmonids may be more susceptible to predation by gulls (Lams spp.) and northern pikeminnow (Ptychocheilus oregonensis) than in the main river channel. Contract no. W66QKZ83437725