APPLICATION OF HISTORICAL GEOSPATIAL DATA AND FIELD- BASED WORK TO MONITOR RATES OF EROSION ALONG THE BLUFFS OF SHADES BEACH IN ERIE PENNSYLVANIA

Bluff erosion rates along the southern Lake Erie shoreline are imperative for land use planners. To help constrain those rates, we have undertaken a combined geospatial and field- based approach at two sites in Erie County, PA. Here we focus on Shades Beach in Harborcreek Township, PA. The bluffs at this location are ~25 m high and consist of a 2 meter layer of Devonian-aged shale that is exposed above lake level at its base. This is unconformably overlain by ~20 m of Ashtabula Till that consists of diamict has and contains intermixed clay to boulder sized materials. The top of the bluffs are about 2 meters of paleo-Lake Erie beach sands, which lay conformably on top of the Ashtabula Till.

The process of mapping the area began by sketching a top view of the whole area of the bluffs, and then the areas which had scarps that we were concerned with has side profiles sketched. After the sketching process, we collected GPS points along the edge of the bluffs in order to bring those points into ArcMap 10.8 to make an outline of the bluff edge. We compared the points that we collected to LiDAR data (2007; ~1 m horizontal resolution) and a 2018 air photo that clearly showed the bluff edge in order to trace the bluff edge and determine the rate of erosion. We are utilizing ongoing trail camera footage to monitor the bluff edge. We will also be utilizing dendrochronology to age and cross-date specific events to better understand past erosional events.

Between 2007 and 2022, total erosion of the bluff edge varied from 0- 5 meters (avg 0 - 0.33m/yr), which is consistent with reported field-survey derived values by the PA DCNR. Our results show there are multiple ways of accurately measuring bluff erosion rates -in the absence of field-based surveys, air photos and LiDAR will also help constrain erosion rates. However, the amount of time between when air photos and LiDAR are collected is large making it difficult to keep on top of erosion rates. In addition, most erosion is happening on the bluff face and not so much at the top of the bluff edge. Our work is consistent with all previous studies that show the bluffs to be susceptible to erosion. Erosion at Shades Beach is ongoing but will likely continue to be slower than other coastal sections in this region.