Transverse Slope of Bed and Turbid-Clear Water Interface of Channelized Turbidity Currents Flowing around Bends

Abstract

Turbidity currents are sediment-laden bottom flows in lakes and the ocean that derive their momentum from the force of gravity acting on the sediment held in suspension. These currents are capable of creating highly meandering channels extending over hundreds or thousands of kilometers. The planforms of these channels show a remarkable resemblance to those of meandering rivers. In order to understand the flow of turbidity currents in sinuous channels a simple analysis of steady, streamwise-uniform flow around a bend of low, constant curvature is considered. The analysis is applied to both a river and a channelized turbidity current. In both cases the bed of the channel is sand, and both sand and mud are carried in suspension. The sand requires turbulence in order to be held in suspension, but the mud is sufficiently fine to allow it to be carried as wash load. The flow is assumed to be Froudesubcritical, and in the case of a turbidity current a relatively sharp interface between turbid water and clear water above is assumed. The analysis focuses on the processes that maintain a) the transverse water surface or interfacial slope associated with superelevation around bends and b) the transverse bed slope created by scour on the outside and fill on the inside of bends. In the case of rivers, the processes maintaining these two transverse slopes can be decoupled, allowing for the use of standard formulations. In a turbidity current, however, the processes may be strongly coupled, especially when the concentration of sand in suspension decreases strongly in the vertical.