CLIMATE INFLUENCE ON LAKE ERIE NEARSHORE-SEDIMENT ACCUMULATION AND BEACH PROGRADATION: A LOOK AT OHIO HARBOR JETTIES AND ADJACENT HEADLAND BEACHES

Erosion problems for the sediment-starved U.S. Lake Erie shoreline reflect the lake’s shallow nature, water-level changes, bluff exposures of unconsolidated glacial and glaciolacustrine materials, human influences, and lake orientation with respect to prevailing wind, wave, and current directions. Despite the absence of substantial nearshore sand sources, sections of the southern Lake Erie shoreline have prograded over the last 100 years in response to jetty construction and sand trapping. This study investigates the evolution of two actively prograding beaches along the Lake Erie shoreline of Ohio: Mentor Headlands Beach and Walnut Beach.

A total of 56 nautical charts of the harbor areas from 1901 to 2005 were georeferenced to provide insight into the timing of hard structure installation, historic shoreline positions, and temporal changes in nearshore bathymetry. Nearshore-surface models, gridded from bathymetric points in ArcGIS using a nearest neighbor interpolation algorithm, provide net-change maps. Bathymetry was not surveyed as regularly as shoreline position, providing only three time-slices per harbor area over the 100-year timeframe of interest; however, nearshore-surface models document a lake-ward translation of shoreline and nearshore environments through time with little change in shoreface morphology. Beach area gained is therefore utilized as a metric for volume change in our timeseries analysis.

Our studied beaches show a paralleled evolution with respect to shoreline progradation and nearshore sand-volume gain, which does not appear to correlate to anthropogenic activity, but could reflect a decadal-scale climate variance. A pronounced decrease in beach gain from the mid-1930s through the late 1940s coincides with regional drought conditions, lower lake levels, and possibly milder wave climate. Historic lake levels have fluctuated between ~173 and 175 meters above mean sea level since 1901 with similar low-level periods in the mid-1960s that do not show a change in the rate of beach progradation, warranting an investigation into whether changes in nearshore-sediment supply by either reduced bluff erosion or longshore transport play a role.