INFLUENCE OF LAKE LEVELS AND HARD STRUCTURE ORIENTATION ON THE GEOMORPHOLOGY AND STRATIGRAPHY OF OHIO’S HEADLAND BEACHES: A GPR-BASED INVESTIGATION OF BEACH PROGRADATION

Beaches have formed over the last century on the up-drift side of harbor jetties along Ohio’s sediment-starved and heavily armored shoreline. Net progradation at Headlands Beach and Walnut Beach has occurred since the installment of jetties in the early 1900s due to the interruption of littoral transport by these hard structures, which have dictated the bounds of beach form. Sediment flux to the littoral system is heavily impacted by lake levels; higher lake levels supply the nearshore with more bluff-derived sediments, whereas lower lake levels limit sediment supply. Processes impacting headland-beach profiles are reflected in the subsurface.

Ground-penetrating radar (GPR) was collected along dip-oriented transects across each headland beach with a pulseEKKO Pro system from Sensors and Software, Inc., utilizing 200 MHz antennae. Historic shoreline positions, derived from georeferenced aerial images, serve as a chronologic control along GPR transects. Changes in lake-level position, sediment input, and accommodation-space distribution are captured in the depositional record of the beaches as variances in clinoform geometry.

Selective preservation of prograding clinoforms can be generalized as a function of lake level: Higher lake levels preserve the depositional record at headland beaches, whereas lower lake-level conditions subject them to sub-aerial processes, resulting in the truncation of clinoforms. As a result, only the foreset is imaged since the topset is acted upon by aeolian processes. The bottomset was rarely resolved using the 200 MHz antenna. The foreset dip angle of lakeward-inclined reflectors decreases lakeward of the 1960s shoreline position. This change correlates with a shift in hard structure orientation. Accommodation-space distribution, as determined by hard structure orientation, is therefore an intrinsic control on prograding headland-beach stratigraphy along Lake Erie’s southern shore.