CGRG Bibliography of Canadian Geomorphology
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Author : Davidson-Arnott, D.G.D.; and Langham, D.R.J.
Date : 2000.
Title : The effects of softening on nearshore erosion of a cohesive shoreline.
Publication : Marine Geology
Issue : 166(1-4):
Page(s) : 145-162.
Abstract
A study designed to measure spatial and temporal variation in the shear strength of the surface of a till substrate in the nearshore was carried out on the south shore of Lake Ontario, Canada. The primary goal was to determine whether softening, or reduction in shear strength, occurred during the study period, and the significance of this as a control on the overall rate of vertical lowering of the cohesive profile. Characteristics of the nearshore environment and the substrate were determined through the collection of till shear strength measurements, substrate cores, and surficial sediment thickness along a 300 m long underwater profile. Changes in shear strength were monitored over a four-month period in experimental plots in water depths of 1.6, 3.5 and 4.75 m, together with measurements of bed erosion. Softening of the till was evident from cores which showed a rapid increase in strength and corresponding decrease in moisture content to a depth of about 0.1 m below the till surface after which they became constant. Shear strength of the exposed till surface decreased during periods of low wave activity, and similar results were found in laboratory experiments. Periods of high wave activity resulted in the removal of a layer of softened material, thus exposing harder underlying till. The results suggest that erosion during a storm is related to the thickness of the softened layer that develops during non-storm periods. Because of the steep increase in strength with depth below the till surface, maximum erosion during a storm is generally <1 cm. The spatial and temporal variation in softening of the till surface is complicated by consolidation that appears to occur when the surface is protected from low wave action by the accumulation of surficial sand and gravel in the form of a nearshore bar.
Bibliography of Canadian Geomorphology