ANALYZING THE COASTAL GEOMORPHIC RESPONSE OF REMOVING HARD SHORELINE ARMORING USING BOAT-BASED LIDAR

Beach restoration in Washington State is an important initiative that can benefit forage fish and species that rely on their existence such as salmon and orcas. However, more studies are needed to analyze the effects of restoration projects on the coastal geomorphology. Coastlines along the Washington Salish Sea are dominated by bluffs composed of glacial and nonglacial Pleistocene sediments. Bluff erosion by marine and subaerial processes provides the principal contribution of sediment to nearby beaches and is important in maintaining a healthy beach habitat for many species such as forage fish. Bluff erosion is also a threat to landowners and is often mitigated by installing hard armoring at the base of bluffs. Hard armoring can lead to increased beach erosion, less sediment input from bluffs, and degradation of nearshore habitat.

To restore the natural bluff erosion process and forage fish spawning habitat at Edgewater Beach, 241 m of concrete and rock armoring was removed in 2016. In this study, we investigate the effects of removing hard armoring by analyzing the Edgewater drift cell beach and bluff morphology over six years. To do this, we analyze boat-based LiDAR from 2015, 2017, 2019, and 2021 collected by the Washington Department of Ecology Coastal Monitoring & Analysis Program. Results from this study include digital elevation model surface differencing and sediment volume contributions from the bluffs to the beach over time. Preliminary results show an initial influx of sediment from the bluffs to the upper beach of the restoration site following armoring removal. However, beach elevation between 2015 and 2021 decreased an average of 3 cm at the restoration site. Analyses and results from the study can be applied to other beach restoration projects, land-use planning, and hazard recognition in coastal areas with glacial bluffs.