Elwha dam removal sediment, and what it teaches us about shoreline processes and beach maintenance in the Salish Sea

Removal of two dams on the Elwha River between 2011 and 2014 delivered more than 5 million tons of sand and gravel to the coast of the central Strait of Juan de Fuca in Washington State. This massive sediment nourishment transformed the coastal landscape near the Elwha River mouth and led to a measurable beach response both to the west and to the east of the river mouth. The patterns of coastal response to this elevated sediment input provide insights relevant to a variety of management questions associated with shoreline processes in the Salish Sea. Shoreline evolution data for the Elwha delta published in 2019 and shoreline morphology observations from Ediz Hook (at the distal end of the Elwha littoral cell), paint a picture of a complex beach response to the sediment nourishment associated with dam removal. Notably, the beach response to nourishment did not occur at uniform rates in space or time. Nearer to the source (the Elwha River mouth), the beach response due to nourishment appears to have been initiated by river bar formation and evolution processes, before proceeding along the beach fringing the Elwha River delta at rates of between 1 and 5 meters/day. Evidence will be presented suggesting that, as of August 2019, the beach at the base of Ediz Hook, roughly 8 km from the Elwha River mouth, is responding to nourishment from the removal of the Elwha River dams. Finally, these data point to some interaction between nourish material and armoring on the shoreline; specifically, armoring appears to have inhibited beach response to nourishment locally (i.e. adjacent to the armoring on the beach), but also possibly downdrift of the armoring. These observations may help to improve conceptual models of shoreline processes applied in management and restoration contexts in the Salish Sea.