Toe erosion of glacial till bluffs: Lake Erie south shore

Abstract

Toe erosion and rates of recession of the toe were measured at four sites along a 3.5 km long stretch of shoreline on the south shore of Lake Erie from April to December 1986. The shoreline consists of bluffs ranging from 5 to 12 m in height and developed in overconsolidated till. Toe erosion was measured at peg lines consisting of pins driven horizontally into the face of the bluff at 0.25 m intervals to a height of 1.75 m above the beach, and steel rods driven vertically into the beach with a spacing of 1.5 m. At each site three lines were established and monitored at 1–2 week intervals. Because of record high lake levels, beaches in front of the bluffs were generally <5 m wide, and some erosion was measured on all but three occasions. Recession of the toe during any measurement period was generally 2–6 cm, with the maximum recorded being about 12 cm. Wave action during high-magnitude storms resulted in erosion occurring much higher up the bluff face than for low-magnitude events, but the actual recession of the toe was not substantially greater. A multiple regression model shows that there is a significant relationship between toe recession and several variables that indirectly control wave energy at the bluff toe. However, factors such as beach width and thickness of beach sediment did not have a significant influence on recession rates in this study, likely because the high lake levels resulted in very narrow beaches at all four sites throughout the study period.