Dynamics of Turbidity Current with Reversing Buoyancy

Abstract

In nature and industry there are many situations in which dense sediment-laden currents are overlain by fluid of density intermediate between that of the bulk suspension and of the interstitial fluid. An experimental investigation of such horizontally spreading turbidity currents at a constant inflow rate has been conducted. If the bulk density of such currents is initially larger than the ambient density, an underflowing gravitational turbidity current results. However, once the sediment in the suspension settles out, the current releases buoyant interstitial fluid through the interface between the current and the overlying ambient fluid. This settling of the sediment and the detrainment of buoyant interstitial fluid decreases the spreading velocity of the turbidity current until the current stops and lifts off the bed. The rising interstitial fluid accumulates at the free surface to form a new buoyant surface overflow. In this study, simple spreading relationships based on experimental observations are presented and measurements of the spreading rate and the location of the liftoff distances of turbidity currents made in a horizontal flume are in good agreement with the predictions from these relationships.