This is my personal opinion... no data to back anything up. only my best uneducated guess.
1. there would be an innitial reduction in the productivity of Lower Columbia Chum salmon as their spawning grounds would be high and dry
2. there would be an increase in down river juvinile migration and if ocean conditions allowed larger runs as a result
I think more important than removing mainstream columbia dams you'd increase runs more by eliminating dams that completely block access to spawning grounds. Dworshack on the North clearwater, the dams on the north lewis, cowlitz,white salmon,deschutes, sandy ect. ect. etc. Also along with the removal of these dams a laege campaign to replace culverts to provide fish passage would help. Probably the single best thing we could do for salmon and steelhead in the columbia basin would be to stop hatchry plants and harvest. As hatchery plants mask the real problems with wild fish and as a result of these large but unhealthy runs too many wild fish are harvested.