The final decision variable is listed at the top of this summary page– Reservoir outmigration. Ken and I added this component just recently to address problems that adult adfluvial bull trout sometimes encounter when the reservoirs are drawn down in the late summer and they are seeking to ascend their spawning streams. I had a lot of data from the past six years where I had noted, for specific dates, what I believed were impassable conditions in the lower reaches of several spawning tribs where they flow across the exposed reservoir beds. I also had discharge data for particular streams and was able to retrieve both reservoir volume and total inflow records for the different reservoirs from the hydromet. With this information we were able to determine certain trends and were able to cobble together relationships between reservoir volume and inflow that enabled us establish passage thresholds which could be entered into a binary look-up table. One note: we only did this for Kachess, Keechelus, and Rimrock. What goes on with bull trout in Cle Elum remains a mystery and passage problems associated with reservoir levels have not been noted for bulls leaving Bumping.

The scores are derived very simply. Here you have the adult passage window. The model tallies up the days within that window that the impassable threshold was reached, again based on reservoir level and inflow, for both the baseline and whatever alternative is being evaluated and calculates the percent change. You will notice in this particular example that the alternative resulted in more impassable days for all three reservoirs. Only Rimrock is flagged, and the model does this for you, because the percent change was 10% or greater.

One more thing I’d like to point out here is that if criteria are supplied for any juvenile passage facilities which might be constructed in the future, these could be incorporated in the DSS and a similar output could be derived. Would be very easy to do.