SHORELINE RESPONSE TO RECENT LAKE LEVEL FLUCTUATIONS ALONG SLEEPING BEAR DUNES NATIONAL LAKESHORE

Recent high Lake Michigan water levels induced rapid coastal erosion, resulting in beach narrowing, dune loss, and bluff collapse. These responses were documented anecdotally throughout the entire Lake Michigan basin, however, few studies have quantified shoreline response to rising lake level over large spatial scales (> 1 km) and none have documented shoreline behavior during both rising and falling lake level. To address this gap, we tracked shoreline changes from 2010 through 2024 along the entirety of Sleeping Bear Dunes National Lakeshore (SLBE) using NAIP aerial photographs and Planet satellite imagery. SLBE has a diversity of shoretypes including sandy beaches backed by dunes, tall bluffs, and mixed sand and gravel rivermouth bars. The water line was digitized along SLBE from the imagery and shoreline changes were calculated along shore normal transects using the Digital Shoreline Analysis System (DSAS). Results indicate that most of the shoreline at SLBE was continuing to build lakeward during the period from 2010 to 2014 as lake levels fell to record low levels. During the rising limb of lake level, from 2014 to 2020, nearly the entire park experienced shoreline retreat and beach narrowing. In many locations, the beach was entirely lost and the shoreline intersected foredunes and bluffs, resulting in erosion of these features. Once lake level began to recede, the shoreline in some locations migrated quickly lakeward while other locations recovered shoreline position slowly or not at all. Along areas adjacent to headlands such as Sleeping Bear Point, shoreline position only returned to the pre lake level-rise position once an influx of littoral sediment reached that location. This was accompanied by headland rotation and a general eastward migration of coastal sand deposits, presumably in response to prevailing waves and currents from the southwest. The results of this shoreline change analysis were used to divide the shoreline at SLBE into various shore response categories that provide park managers information on expected future responses and can help guide management actions.