Some good information!

Other factors that influence the degree of damage being done during high water events/redd scour.

One is the length of time higher water events - the longer the flows are evaluated the more damage done.

Another is the size of substrate that the eggs are buried under. A large female Chinook eggs that under head size rocks are less prone to flood damage than eggs under fist size rocks.

As water sheds unravel it is not uncommon to find increase materials moving in the stream channel; both increases in small sediments and over volume of material moving. This tends to increase egg and even fry survivals over the situation of smaller bed load movements.

Another aspect that rarely talked about is the frequency of the larger events. Historically a fish population would typically have decades to recovery from a major event. With increased frequency of those large events on many basins what historically might be considered a 50 flood maybe now be occurring once a decade rather than a couple times a century.

Finally historically fish like Chinook had a high productivity; that is to say if for some reason like a large flood where the population was reduced to a low level that brood year might produce a 10 to 15 time fold abundance increase in a single generation. In some of our more compromised freshwater portion of our basins that productivity may have been reduced by as much 5 fold. The rebound of a stressed population can take much longer than historically.

Across the Puget Sound region through the smolt trapping on a number of rivers the relationship between flows during egg incubation and the numbers of resulting migrants has been established. The range of response between that survival and egg to migrant survival varies significantly between those basins. A measure of the health of the basins?

Finally the Stillaguamish has become the poster child illustrating the impacts from flood on Chinook survivals. Looking at the increase frequency and magnitude of peak flows in the basin underlines why Stillaguamish Chinook have become such a limiting stock for PS fisheries.

Curt