Erosion and Sedimentation Along a Cohesive Shoreline – The North-Central Shore of Lake Erie

Abstract

A study of the distribution and texture of bluff and nearshore sediments of north-central Lake Erie was carried out to measure the patterns of erosion and sedimentation characteristic of a cohesive shoreline. Onshore deposits of the study area consist mainly of bluffs of cohesive glacial sediments standing at the waterline or separated from it by narrow intermittent beaches. The nearshore deposit is a narrow band of gravel to clay-sized postglacial sediment located between the shoreline and a broad offshore shelf of exposed glacial sediment. The width of the deposit increases from west to east and there is local widening and beach development at the three harbour areas of Ports Stanley, Bruce, and Burwell as the result of entrapment and diversion by harbour structures. A new sediment budget proposed for the reach shows an annual input of 6 × 10 6 tonnes of silt and clay and 2 × 10 6 tonnes of sand and gravel. Bluff erosion accounts for 89% of the sediment supply and nearshore-slope erosion and stream discharge for 10% and 1%, respectively. Although harbour structures have increased the volume of nearshore sediment retained by the reach, their effect on the sediment budget is minimal because of the high supply and transport rates. More than 99% of the sediment input is lost to the shoreline to the east and to the offshore basins by transport within the nearshore zone. The sediment remaining within the reach is coarser and better sorted than the source materials and appears to be stable in pattern and texture over the short term (1973–1979).