It is often said that a big winter water will "wash out the kelts". However a kelt will only return to the sea when it's metabolism is ready for such a change. ie...the return to a feeding mode in salt water.
With regard to kelts returning to spawn again it is interesting to note scale sampling has shown that, on average, only 2% of a seasons catch consists of second time spawners.
A concern of a big winter spate is the potential of gravel movement,thus resulting in redds being washed out. Fry may also be stranded in puddles left in fields, after the river drops again.