To all with interest: There is a fairly recent study/report on the accumulating sediment load in the Stillaguamish river over the last several decades that should be must reading. I'm sure Jason is well aware of it. I don't have the link at my fingertips, but a search should turn it up. Disclosure: Nonscientific conjecture to follow-- I've often wondered whether sediment load accumulation in a river bed is as natural a process as an alpine lake becoming a meadow over geologic time, but flood control structures in a river which prevent the river being able to "vomit" its sediment load onto the adjoining flood plain likely accelerate the sediment accumulation. In any case, it eventually overlays the spawning beds in low gradient sections of the river. Thus flood control and healthy spawning habitat may be at cross purposes in some systems.