HIGH-RESOLUTION MULTI-TEMPORAL 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 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 using high temporal and spatial resolution lidar 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. Shoreline positions are extracted from digital elevation models generated from lidar surveys conducted in 2001, 2007, 2011, 2015, May 2018, and September 2018 using the ordinary mean high water mark (75.4 m). We applied the Digital Shoreline Analysis System of Himmelstoss et al. (2018) to compute alongshore variability in shoreline position on transects spaced 50 m apart, perpendicular to the Lake Ontario shore. Alongshore rates of change in shoreline position were quantified over three intervals: 2001-2015, 2015-September 2018, and 2001-September 2018. The mean change in shoreline position was 0.04 m/yr, -0.07 m/yr, and 0.03 m/yr, respectively, where positive rates of change represent depositional shoreline advance and negative, erosional shoreline retreat. Only the 2015- September 2018 interval signaled average retreat, likely the highlighting the influence of high lake levels in 2017. The most pronounced change in shoreline position occurred on either side of the channel inlet, where the shoreline prograded on the southern spit and retrograded on the northern spit, which is consistent with northward longshore transport. Future work will include the addition of 2020 datasets collected using a small unmanned aerial system. Additionally, volumetric changes in erosion and deposition, and fluctuations in foredune crest position and elevation, will be measured from both the lidar and photogrammetric datasets.