Delineating and monitoring bluff toe positions from boat-based lidar to quantify morphology change at Edgewater Beach, WA

The Washington State Department of Ecology Coastal Monitoring & Analysis Program (CMAP) has performed a total of four boat-based lidar surveys of a shoreline restoration project at Edgewater Beach in South Puget Sound where approximately 800 feet of shoreline armor was removed in 2016 from the base of a historic feeder bluff. Surveys were conducted in 2015 approximately one year before the restoration, 2017 approximately one year after the restoration, and additional surveys in 2019 and 2021. Boat-based lidar data were collected along the entire length of the drift cell to generate digital elevation models to determine beach morphology change throughout the entire drift cell. Boat-based lidar is an optimal tool for collecting upper beach features at Edgewater Beach because the horizontal look angle of the vessel-mounted laser scanner has an unobstructed view of shoreline armor and the bluff under the overhanging vegetation, unlike traditional airborne lidar. Detailed topographic cross-shore profiles at the project site were compared between surveys and beach width and slope was extracted to quantify the changes to the beach and bluff as a result of the restoration project. Bluff toe elevations and horizontal positions for each profile were selected based on a quantitative set of parameters. Along the location of the previously armored shoreline, the bluff toe translated landward and upward relative to the armor toe and Mean Higher High Water (MHHW), which has enabled the development of a backshore area following armor removal. The backshore zone provides important ecological services--refuge, foraging, spawning, roosting, and nesting, thus measurement of the armor toe and bluff toe elevations relative to MHHW are key to assessing ecological impact of shoreline armor and ecological lift following shoreline armor removal.