Mapping Recent Coastal Shoreline Changes in Southwestern Alaska Using Landsat 8 Satellite Imagery

Marks, S. and Potter, C., 0000. Mapping recent coastal shoreline changes in southwestern Alaska using Landsat 8 satellite imagery.Coastal communities in Alaska are frequently subjected to storm surges that erode shorelines and riverbanks, which increases flood risks around critical village infrastructure. Coastal erosion in western Alaska may be occurring currently at rates as high as 15 m per year, but the region has not been mapped in enough detail to accurately assess recent shoreline and inland riverbank erosion rates. To update the mapping of changes in all of SW Alaska's coastal margins, Landsat 8 satellite imagery was analyzed to detect trends in the normalized difference water index collected from 2013 to 2023. The normalized difference water index values range from -1 to 1, with negative values indicating majority land that includes soil and live vegetation cover and positive values indicating majority water coverage. Results showed marked coastal shoreline erosion at Chagvan Bay, Hagemeister Island, and Nanvak Bay over the past decade. Additional locations of recent bank erosion were detected on the Kuskokwim River, from its upriver mouth past the city of Bethel. Riverbank erosion was also detected in northern Nushagak Bay, and extensive surface-wetting trends around wetlands and riverbanks were detected near the village of Togiak. Moreover, many villages on the west coast of Alaska and in the Kuskokwim River Delta have recently documented climate change case studies highlighting bank erosion, indicating that a variety of related ecological disturbances are ongoing across the region.