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Safety of salmon nest sites in changing climates

Date: April 21, 2015

Predictions of future climates include higher flows in mountain streams during mid-winter; a time when salmon eggs are incubating in streambed gravels

The eggs of fall-spawning Chinook salmon are buried and incubate in the beds of mountain streams over the winter months when flows are very low and there is limited bed scour and sediment transport. Some have argued that in future climates these landscapes will have less snow and more mid-winter rain, which could lead to bed scour and destruction of the egg nests. We have tested this hazard by multi-dimensional modeling of bed shear stresses supported by unique high resolution stream bathymetry derived from an experimental airborne green lidar sensor. We find that because many of these streams are unconfined, low gradient and carry large gravel on their beds, they are not very vulnerable to this hazard. When model discharge is increased, water flows over the banks and into the surrounding floodplain, which acts as a buffering system that limits how much the shear stress can increase. Under even extreme flows with a recurrence interval of 10 years, the stream bed, which was modeled after channels in the upper Middle Fork Salmon River, Idaho, did not scour, and thus any salmon egg nests would have not been disturbed.

Principal Investigators: 
External Partners: 
Daniele Tonina – Univ. of Idaho, Center for Ecohydraulic Research