There was a fairly substantial engineering study done on the lower dam by the USGS concerning how to manage the breaching to avoid damage to the lower river from sediment. It would be lowered in stages, if I remember correctly. There was also a biological study of the current fish distribution above both dams, so there will be "before" and "after" data on the fish community. Pretty obvious there will be anadramous fish then that there are not now, but the effect on resident fish, e.g. bull trout, is an issue as well. If I remember, Gorton's original position was to take out the lower dam first and see what that does to spawning; trouble is, there is little or no quality spawning habitat in the reach between the dams--an approach fated to show failure. Both need to come out.