Relating Forage-Fish use With Spatial and Temporal Variability of Particle-Size Distributions of Mixed Grain-Size Beaches in the Elwha and Dungeness Drift Cells , Central Strait of Juan de Fuca, Washington State.

The removal of two dams on the Elwha River of Washington State is expected to release 1.38 x107 m3 of gravel, sand and silt into the Elwha River and nearshore marine environment of the Strait of Juan de Fuca (Randle et al., 1996). Waves and tides are expected to distribute these sediments widely upon beaches within the Elwha littoral cell with implications for many biotic organisms including forage fish such as surf smelt (Hypomesus pretiosus) and sand lance (Ammodytes hexapterus)(Shaffer et al., 2008). Forage fish spawning surveys (Moulton and Penttila, 2000), consisting of beach foreshore surface photographs and bulk sediment samples allow correlation between sediment particle-size distributions and forage-fish egg frequencies. Seasonal and spatial variability of mean grain-sizes of mixed sand-gravel beaches is characterized with traditional sieve (Church et al. 1987) and photographic methods (Adams, 1979). Sample sites are categorized by geomorphic setting (e.g. embayments, bluffs, and spits) and sampling frequency reflects expected annual seasonal variation in sediment transport processes . Mean sediment grain-sizes measured from photographs are correlated with mean grain-sizes from sieved bulk sediment samples. Comparison of mean grain-sizes from surface and 10-centimeter depth photographs where the surface lag has been removed, suggest an improved relationship between bulk sieve sample data and data obtained from photographic analysis. This finding demonstrates that photographic analysis of grain-sizes on mixed grain-size beaches from surface samples only, may skew mean grain-size due to the presence of a surface lag layer. Observed particle-size distributions are strongly polymodal. Geomorphic setting of beaches is an important factor in the observed range of mean grain-sizes based on proximity to sediment sources such as feeder bluffs. These results will be used to compare forage fish habitat form and function response to future sediment inputs from dam removals.