A multi-scale assessment for managing coastal geomorphic changes in southwestern Lake Michigan

Understanding coastal geomorphic change is essential for advancing the United Nations Sustainable Development Goals (SDGs) through a multi-scale coastal management framework. In particular, characterization of coastal geomorphic change across multiple spatial and temporal scales can provide essential insights and context-specific knowledge that can inform and empower local communities. In this study, we present a multi-scale assessment of coastal geomorphic change in southwestern Lake Michigan in the Laurentian Great Lakes. Three spatial scales-county, reach, and transect-and two temporal scales-long-term and short-term-were examined using nine sets of historical aerial imagery spanning 1937 to 2020. The site-averaged long-term (1937-2020) change rates for the bluff crest, bluff toe, and shoreline were -0.22, -0.17, and -0.16 m/year, respectively. In the short term (1995-2020), the corresponding rates were -0.22, -0.15, and -0.32 m/year, indicating an increasing shoreline erosion in recent years. The coastal geomorphic changes at county, reach, and transect scales were further characterized, showing regional and localized distributions of coastal erosion in our study sites. The mechanisms driving coastal change-particularly wave impacts-were also examined to assess their correlation with coastal geomorphic change across different spatial scales. The results indicate that wave impacts influence coastal environments at certain scales more strongly than at others. Several erosion "hotspots" were examined to identify local factors contributing to severe site-specific erosion. Lastly, the spatial uniformity of coastal geomorphology was examined between the county and reach scales. Overall, the findings suggest that multi-scale analyses provide a valuable insight for effective management of coastal geomorphology.