Would be interesting to track periods of extreme water flow and its relation to the fish population. Especially over 1, 3, 5 and 10 years. Who knows, maybe the bottom scouring is necessary to remove certain bacteria whose buildup becomes detrimental to the young fry. You may find yourself in for a salmon resurgence in the next 5 years!!!
I do know this, if there is a positive to be found, you will find it.