Horizontal Transport and Sedimentation by Interflows and Turbidity Currents in Lake Geneva

Abstract

Turbidity currents and interflows are the main mechanisms of transport of suspended particles from rivers to lakes. Turbidity currents originate from singular events—for example, a delta deposit destabilized by unusually high flood waters and its subsequent transport through delta channels to the basin plain. The sedimentation rate maximum is at the end of the channel and decreases laterally from the channel axis. On the basin plain,turbidity currents mingle with the autochthonous sedimentation, which has a sedimentation rate that is smaller by several orders of magnitude.

In contrast, interflow sedimentation rates decrease exponentially with distance from the river mouth. The inflow is affected by Coriolis forces and interflow sediments are dominant in the areas extending to the right of the inflow. The composition of the sediments evolve with distance to the inflow due to different settling velocities of the components.

In the case of Lake Geneva, turbidity currents occur in a Rhone delta channel approximately twice a week in summer (Lambert and Giovanoli, 1988). They are absent in winter. Below the interflow, the sedimentation rates of total solids are about 100, 30, and 5 g m⁻² d⁻¹ at 1.85. 4.75, and 9.3 km from the river mouth, respectively. In the interflow, the composition of particulate matter is similar to that of the Rhone, except the organic matter content, which is four times higher. This is explained by the relatively low settling velocity of organic matter. This interpretation is supported by the observed increase of organic matter content in sediment traps and in bottom sediments with distance. With sedimentation rates of about 0.15 g m⁻² d⁻¹, the contribution of the autochthonous organic matter is minor.