OHIO’S HEADLAND BEACHES: IMPACTS OF LAKE LEVELS AND ICE COVER ON A MODIFIED SHORELINE

The southern shore of Lake Erie is heavily modified, subjected to erosion, and starved of sediment. However, early 20^th century installation of harbor-protecting structures has led to areas of net progradation. Net littoral drift, which trends from W to E across the area, has trapped bluff-derived sediments against these structures, creating headland beaches on their up-drift side. The orientation of these structures greatly influences beach form and progradation rates as a function of changing accommodation-space distribution.

Lake level and ice cover are major geomorphic controls on beach change. High lake levels attack coastal till bluffs and supply the nearshore with more sediment than low lake levels that expose more beach area to protect bluffs. Ice-cover conditions, especially those leading to pressure-ridge formation, represent a mechanism for excavating and transporting coarse sediment from the nearshore beach-ward. To evaluate controls on headland-beach evolution more closely GPR data was collected along dip-oriented transects at three Ohio beaches: Headlands Beach, Walnut Beach, and Conneaut, which are sedimentologically distinct and in different stages of net growth. Auger samples served to ground-truth GPR interpretations while historic shoreline positions, mapped from georeferenced aerial imagery, provided chronologic constraint.

GPR data reveal changes in prograding clinoform geometry, attesting to the dynamics of headland beaches, which have been impacted by episodic erosion and deposition. Multiple regression analysis of net beach growth, derived from shoreline positions, versus lake level and ice cover suggest that high lake levels are more strongly associated with beach growth overall, despite sedimentologic differences. This is due to increased sediment fluxes from nearby bluffs. Ice cover appears to play a secondary, but important role in headland evolution as a transport mechanism while the bounds of beach growth are ultimately dictated by accommodation space, a function of hard structure design.