Coastal Zone Mapping along the Elwha Drift Cell, Central Strait of Juan de Fuca

During the summer of 2015, the Washington State Department of Ecology Coastal Monitoring & Analysis Program (CMAP) conducted two surveys to map the beaches, bluffs, and nearshore region of the Elwha Bluffs and Ediz Hook coastline in the central Strait of Juan de Fuca near Port Angeles, Washington. This work, funded by the US Army Corps of Engineers, provides the ability to assess shoreline change within one season over a 4-month timespan. High-resolution topographic and bathymetric data was collected using boat-based lidar and dual-head multibeam sonars aboard the R/V George Davidson, with additional topographic data collected by foot using GPS on backpacks to fill in shadows from the lidar and walk cross-shore transects. By employing these methods, seamless coastal zone mapping from bluff top to over 10-m water depth was achieved. These data sets represent the first ever drift-cell scale comprehensive and detailed mapping of both coastal bluffs and the nearshore. Together, the surveys enable assessment of bluff sediment supply to beaches and the dispersal of sediment through the nearshore zone. While the interval between surveys was relatively short, significant human-induced and natural erosion of the Elwha bluffs was observed between June and October. In particular, the massive reshaping of the bluff face and uplands at the Port Angeles landfill (still in progress) provides snapshots of prior conditions of the bluff, beach, and associated seawall along a portion of the project site. These data also provide an essential baseline for assessment of anticipated increased littoral sediment supply resulting from the removal of the Elwha dams and can be used in conjunction with previous nearshore and beach profile data collected by the US Geological Survey and CMAP before and after dam removal. The change analysis to date suggests sediment from the delta is beginning to make an imprint in the nearshore fronting the Elwha bluffs, with sand blanketing lower intertidal cobbles and initiating the choking of kelp beds