In the Stillaguamish River basin, low flows and high temperatures have been identified as a barrier to Chinook and coho salmon recovery, and will only be exacerbated with climate change. Increasing the extent and water storage potential of groundwater-fed floodplain channels has the potential to buffer salmon vulnerability to high stream temperatures, by creating cold-water habitat in side channels and in main stems downstream of cold-water seepage zones.
The purpose of this project is to build upon existing knowledge and priorities from the Stillaguamish Tribe and Snohomish County to identify where floodplain restoration would provide the greatest increase in salmonid habitat through the creation of groundwater-surface water interactions. It will involve a reach-scale study of habitat conditions and salmonid occupancy of main stem and adjacent side channels on the Stillaguamish River, to determine habitat attributes that are correlated with Chinook and coho spawning and late summer coho survival. The Stillaguamish Tribe and Snohomish County will be able to use the study results for future modeling of groundwater-surface water interactions and in the evaluation of large wood installations planned for 2019.