LAKE ERIE HOLOCENE COASTAL EVOLUTION NEAR THE PORTAGE RIVER-CATAWBA ISLAND, OHIO

The Portage River delta appears to satisfy the criteria for a new sedimentological model of asymmetric deltas where the discharge of the river interferes with the longshore drift cell, causing strandplain growth on one side of the delta mouth.  Aerial photographs from the 1930s-1940s show a strandplain (accretionary beach ridge complex) east of the Portage River connecting Catawba Island (a bedrock feature) to the mainland.  In contrast, the coastline west of the Portage River consists of a few, thin accretionary beach ridges separated by coastal wetlands.  This study used 29 vibracores up to 4.5-m in length to study the Holocene history and evolution of this region.  Vibracores from the strandplain east of the Portage River consisted of sandy deposits about 4-m thick overlying glacial till.  These sandy deposits are interpreted as a shallowing-upward sequence (shoreface overlain by beachface overlain by backbeach dune and thin wetland deposits) evidenced by sedimentary structures such as lakeward and landward dipping laminae, alternating heavy mineral laminae and quartz sands, and trough cross-bedding.  In contrast, vibracores from west of the Portage River showed a single accretionary beach ridge sequence about 1-m thick overlying compacted peaty sediments about 1-m thick, which in turn overlies glacial till.  The marked contrast east and west of the Portage River mouth suggest the river itself is strongly modifying coastal processes and nearshore sand budgets.  These results have significant implications for coastal management in the Great Lakes, indicating the importance of understanding baseline processes prior to evaluating anthropogenic effects.