GEOMORPHOLOGY OF OHIO’S LAKE ERIE HARBOR-HEADLAND BEACHES: INFLUENCES OF CHANGES IN ACCOMMODATION-SPACE DISTRIBUTION

Littoral sediment trapping has formed extensive strands against western sides of breakwaters at Fairport, Ashtabula, and Conneaut harbors, situated along an ~70 km-long stretch of NE Ohio’s highly erosive, bluff-dominated shoreline. Combined sand sequestration at these depositional headlands has exceeded 110,000 m³ annually since breakwater completion in the 1910s. An investigation is underway to better understand headland-beach geomorphology, evaluated as a function of varying breakwater orientations and lake-level changes.

Dip-oriented GPR transects, collected across the strands with 200 MHz antennae, resolve prograding clinoform geometries within the upper 4 m of the subsurface. Lakeward-inclined foreset beds mimic modern foreshore geometries while topset beds are largely truncated by near-horizontal, parallel reflections that suggest continuous surficial reworking of the upper meter by modern aeolian and anthropogenic processes. Completely intact clinoform shapes coincide with paleoshorelines deposited during low lake-level periods while aerial photographs reveal that largely uniform rates of strand progradation are punctuated by episodes of stunted beach growth, coinciding with shorelines reaching changes in breakwater orientation.

The studied harbor-headland beaches currently exist in different evolutionary stages with respect to thresholds in accommodation-space distribution. Following decades of growth, Ashtabula’s beach had completely filled its confined accommodation space by the mid-1970s, whereupon its shoreline position remained unchanged beyond seasonal variances. Fairport’s headland beach underwent a pronounced decrease in growth rate in the mid-1970s as its shoreline lengthened abruptly by ~30% after having reached a change in breakwater orientation. Beach progradation here continued at a reduced rate and will likely continue until the breakwater terminus is reached. Conneaut’s beach has built lakeward at a near-constant rate as its shoreline has yet to encounter one of several changes in breakwater orientation. While lake-level fluctuations govern regional changes in accommodation-space distribution at the headland-beach shorelines, highly varied breakwater orientations impart a strong site-specific imprint on shoreline behavior.