They will survive well enough. The old rule was river at at flood stage and 4 inches of additional rain comes in 24 hours you will have a hundred year flood. Right now we are below average so the streams in the Chehalis will absorb the flows.

After that no idea but if I remember the previous two events in upper Satsop had nearly 12 inches of rain and add the coming storm with around 5 inches and you get 17 inches South Olympics BEFORE November! That is one really bad set of weather patterns and long range forecast is for this to be the winter storm pattern.