Bluff Retreat and Sediment Input to a Sand-Starved Littoral System on the Pennsylvania Lake Erie Coast, USA

Coastal bluff retreat is a significant hazard for the eight US states on the North American Great Lakes. Highstands in Lake Erie water levels during 2019 broke long-term records along the Pennsylvania coast, which both raised public awareness of coastal hazards in general and will likely lead to enhanced bluff retreat due to wave-driven steepening of the coastal profile. While building-loss frequencies are low compared to urbanized areas on the Pacific coast, the relatively undeveloped 123 km coast of Pennsylvania currently has ~$66M of near-bluff property at risk from bluff retreat.

Using T-Sheet and LiDAR derived bluff-crest data for 1938, 2007, and 2015, a Bayesian network model of bluff retreat is being developed for the westernmost of three large littoral cells that define the Pennsylvania coast. The model will identify the relative importance of wave attack; relative groundwater flux; and bluff stratigraphy, elevation, and slope in controlling bluff retreat magnitudes and patterns. Additionally, bluff-face topographies from 2007 and 2015 are being used to better estimate bluff sediment contributions to the littoral system. Bluff erosion is the principal sediment input to all three littoral cells, one of which hosts Presque Isle State Park which is the state’s largest coastal-resource attraction. The project area covers the 35 km-long Western Erie County littoral cell and represents almost half of Pennsylvania’s Great Lakes bluff coastline. Seven sub-sites are being used to model bluff retreat and are integrated with cell-wide surface-difference mapping to quantify bluff contributions to the littoral sediment budget.

Project results will allow improved understanding of the relative importance of factors driving bluff erosion. Results are expected to enhance scientific understanding of bluff failure processes on Lake Erie, aid science-based decision-making by coastal resource managers, and increase hazard awareness within the regional coastal population.