BLUFF RETREAT ON THE LAKE ERIE COAST OF PENNSYLVANIA: ENHANCING PUBLIC PERCEPTION OF HAZARD & BENEFIT

Tall, Quaternary-age, lakefront bluffs along the Pennsylvania coast of Lake Erie consist of unconsolidated glacial-till through paleo-lacustrine and strandplain strata. They overlie Devonian shale bedrock at or just below lake level. Retreat at the bluff crest has been a chronic hazard for over a century, occurring at a long-term average rate of ~0.15 m/yr. Resolving the processes that drive bluff retreat, quantifying relative land-loss hazards, and measuring the benefits of bluff retreat as a sediment source for the littoral system contribute to improved public perception of the hazards and importance of eroding landforms on this Great Lakes coast.

Within the western Erie County littoral cell (WECLC) on the southwestern half of the 73 km PA coast, bluff retreat has been analyzed from several perspectives over the past decade. Bayesian Network (BN) analysis has allowed the bluff system to be modeled and “what if” scenarios to be considered. Results statistically confirm the dominant forcing agents and explain how along-coast changes in retreat rate are linked to environmental variables. An eight-input BN correctly predicted bluff retreat rates 74–95% of the time and with a mean predicted probability of 84%. Recent (through 2015) Lidar DEM data have been differenced to map the patchiness of elevation gain (temporary storage) and loss (permanent erosion) on the bluff face to measure sediment export to the littoral zone. Analysis identifies bluff-failure patterns important to coastal hazard planning, highlights possible feeder-bluff areas, and yields information on sediment budgets for the WECLC and for Presque Isle (PA’s most visited state park) in the downdrift littoral cell. Morphometric analysis (using present, watershed-average, and policy-adopted stable slope angles; stratigraphy; elevation; etc.) combined with 1938–2015 retreat-rate data has allowed development of an online erosion-hazard viewer. Four hazard zones span the landscape between the beach and a line located almost 275 m landward of the bluff and demarcate relative degrees of property-loss hazard. Outcomes from these applied-research efforts are being shared with coastal stakeholders to help improve perception of coastal-erosion hazards over decade–century timescales.