Evolution of a non-cohesive granular bed subject to a succession of erosive turbidity currents

Abstract

An experiment was performed to study the evolution of a non-cohesive granular bed subject to a succession of erosive turbidity currents to evaluate the applicability of a proposed interface model that prescribes a relationship between the bed shear stress and the local bed elevation and local bed slope. This study considered only the relationship between the local bed elevation and the shear stress by using non-cohesive plastic particles as bed sediment that was laid down in a subaqueous straight channel. The elevation of the plastic bed was measured before and after it was subjected to two erosive salt water turbidity currents using a high resolution displacement laser mapping system. These changes in elevation of the sediment bed are compared to determine whether a correlation exists between local bed elevation and bed erosion. The results from this experiment display a weak correlation between the erosion of the plastic bed and the initial local bed elevation when the initial elevation height is small relative to the thickness of the turbidity currents.

(cont.) However, a strong correlation exists when the initial elevation height is approximately 2% to 6% of the turbidity current thickness. The strength of this correlation also depends upon the window size of the analysis which is shown to be associated with the downstream variability in bed roughness.