APPLICATION OF REMOTE SENSING AND FIELD SURVEY FOR QUANTIFYING BLUFF EROSION RATES IN WESTERN ERIE COUNTY, PENNSYLVANIA

Erie Bluff State Park’s (EBSP) shoreline in Western Erie County extends for ~2.5 kilometers and consists of ~30m high bluffs of glacial material that are susceptible to erosion. Lake Erie and its beaches offer many recreational activities which can often be interrupted by bluff erosion. Bluff recession is a major concern to coastal property owners, commercial and residential, as sudden slumping and consistent retreat of the bluff top must be considered before any developmental project can begin. At EBSP, eroding scarps are only meters away from heavily trafficked trails, posing a potential safety concern, and should be continuously monitored. Therefore, understanding and quantifying erosion rates is a critical component of land use planning. We have combined historical geospatial data with current field data to better evaluate the rate and means at which the bluffs at Lake Erie are eroding. Two locations at EBSP were selected for analysis.

To constrain erosion rates, we utilized both field and remote sensing techniques. In ArcMap 10.8 we used LiDAR data acquired in 2007 (~1 m horizontal resolution) and overlaid a 2018 air photo where the bluff edge could be delineated. GPS points taken in June/July2022 along the current bluff edge were overlain on those two images. Measuring the location of the bluff edge in each dataset indicated that the amount of bluff edge lost at EBSP between 2007 to 2022 varied from ~0 to >7 m, giving an average erosion rate of ~0 to 0.5 m/year, which are consistent with rates reported by the PA DCNR in 2018 and 2019.

Further field assessments recognized the remobilization of clay material on the front edge of the bluffs. The erosional process appears to be gradual and follow the natural curvature of the bluff edge. However, we have identified multiple scarps that indicate a sudden transportation of large, consolidated blocks of material, with our largest deposit being 45m³ in volume. These scarps average ~10 m across and protrude ~4 m out from the linear edge of the bluffs. We intend to also use a dendrochronological approach to age and cross date distinct trees to determine specific years in which these events occurred. Our remote-sensing approach combined with field surveys done by the NRDC allow for the most accurate and efficient method of constraining erosion rates.