Longitudinal Patterns of Fine Sediment Infiltration, Fluvial Processes and the Distribution of Chinook Salmon Redds

Fine sediment infiltration into salmonid redds has been shown to reduce egg-to-fry survival when sediments (<2 mm) reach a concentration by weight of 15-20% within the gravel framework.  We investigated longitudinal patterns of infiltration in the upper Yakima River basin (Washington, USA) using buried Whitlock-Vibert Boxes as sediment traps in simulated spring Chinook salmon Oncorhynchus tshawytscha  redds. Assessments of fluvial geomorphology included fine-scale (10-100m resolution) quantifications of physical habitat (depth, water velocity, d₅₀ etc.) and course-scale parameters (1-50km resolution) derived from digital elevation models (DEM), aerial photos and the NetMap community watershed database. Redd locations were mapped from multiple years (2004-2009). Preliminary analysis indicates that mean infiltration during the 2009-2010 incubation period was at least two standard deviations less than what is expected to significantly influence egg-to-fry survival. Correlations between infiltration and both fine and coarse-scale physical data indicated that concentrations of fine sediment greater than 1 mm were driven by features such as valley width and latitudinal and longitudinal position of  the redd within the stream channel.