TIME-SERIES ANALYSIS OF GEOMORPHIC CHANGE ON THE SANDY POND SPIT, EASTERN SHORE OF LAKE ONTARIO, NEW YORK

The Sandy Pond spit (SPS) is a north-south trending barrier island on the eastern shore of Lake Ontario, New York, which responds dynamically to fluctuations in water elevations, ice cover, and storms. Mattheus et al. (2016) reconstructed the geomorphic history of the SPS from 1878-2013, determining that the most significant forcing affecting decadal change is the lake-water elevation. In the summers of 2017 and 2019, anomalously high precipitation and lake levels resulted in increased erosion along the SPS, and flooding in neighboring communities. In this study, we quantify changes in shoreline position, dune crest position and elevation, and volume of deposition and erosion using high temporal and spatial resolution lidar, sUAS, and sonar surveys. Our goal is to develop a process-based understanding of how variations in lake level affect the SPS, which can be used to predict responses to future climate and management changes. Analysis relies on digital elevation models (DEMs) and DEMs of difference (DoDs) generated from surveys conducted in May 2001, July 2007, June 2011, October 2015, May 2018, September 2018, June 2020, July 2020, and August 2020. Alongshore rates of change in shoreline position were quantified over three intervals: 2001-2015, 2015-September 2018, and 2001-September 2018. The adjusted mean change in shoreline position was 0.06 m/yr, -0.78 m/yr, and -0.12 m/yr, respectively, where positive rates of change represent depositional shoreline advance and negative, erosional shoreline retreat. Increased shoreline retreat during the 2015-September 2018 interval is likely attributed to the high lake levels in 2017. Preliminary analysis of the July 2007 to September 2018 DoD indicates a net change in volume of 52,002 m³, equating to approximately 24 cm of statistically significant deposition (CI 95%) distributed over 213,997 m². After completing volumetric and dune crest position and elevation analyses, we will interpret the geomorphic processes at the SPS driving annual morphologic change.