COHESIVE PROFILE EROSION BY WAVES

Abstract

Hydraulic tests of the erosion by waves of a shore profile made from intact samples of till, a cohesive material comprising a large part of the Great Lakes shorelines, have been completed. Over 1000 h of testing in a laboratory flume with random depth-limited breaking waves, varying conditions of sand cover, and varying mean water levels have been run. The vertical erosion rates of the till were measured along the centreline of the 8 m long, 0.35 m wide and 0.25 m thick till profile; its initial shape was the equilibrium form y = Ax2/3 common on sandy beaches. Some of the important findings are that this type of hydraulic test is viable, the role of sand in the erosion process is similar to its role in unidirectional flow model tests but the thickness and volatility of the sand layer are also factors, the main effect of varying water levels is to shift the zone of erosion activity up and down the profile, and that erosion can occur in the absence of sand if the rate of wave energy dissipation is high enough (plunging breakers, steep slopes).