The geomorphic role of large wood in the coastal zone: Mobilization threshold and beach morphology impacts in the North American Great Lakes

While large wood has been extensively studied in fluvial settings, where it functions as a key component of both physical and biological systems, the role of large wood in the shoreline-nearshore zone has received little attention to date. To address this gap, we examined large wood as a geomorphic agent along an eroding beach shoreline of southwestern Lake Michigan using high-resolution orthoimagery and DEM datasets. Erosion of the site and the liberation of woody materials from the strand were enhanced by rising lake levels. We digitized positions and evaluated the physical characteristics of 2627 pieces of large wood from 5 aerial images (2009–2017) and 11 seasonal drone surveys (2018–2020). This high temporal data resolution allowed us to track 374 unique pieces of large wood over time, revealing common transport pathways and sedimentary impacts of large wood along a wave-dominated beach shoreline. Results indicate that, while large wood has local, transient impacts on beach geomorphology, its presence has little bearing on longer-term beach evolutionary trajectories. Large wood offers little natural shoreline protection along high energy, dynamic shorelines, but may promote backshore accretion and foredune growth under other hydrodynamic and sediment-supply conditions. Our analysis of decadal shoreline evolution reinforces the importance of antecedent topography and coastal habitat elevation as primary controls on rates of shoreline recession.