What is the minimum amount of percent of normal snow pack in the salmon drainage basin to get the maximum flush for smolts in the spring?

Answer: 

There is not a simple answer to this question.  First off, spring flow conditions for smolts in the lower Snake River comes from several drainages including the Salmon (Clearwater, upper Snake, and Imnaha are the other large contributors).  Second, the flow amounts smolts encounter on their outmigration are not solely determined by snowpack amount, but also how fast the snowpack melts (the shape of the runoff).  A large snowpack that melts too early doesn't help smolts get to the ocean. A maximum "flush" would occur with a very large snowpack that came off (melted) quickly.  This would not be best for smolt survival because flows would be so high that there would be too much spill over the dams and gas super-saturation would do more harm than the benefits of high flow.  If looking at just snowpack, more is better up to some limit or extreme. There will always be some drier years. As long as we don't see more of those but rather we can hover around the "average" years the smolts have a good chance of surviving to the ocean.
 

Answered on: 
Wednesday, December 16, 2015 - 5:00 PM MST