Sediment transport by turbidity currents

Complete field equations have been established for turbidity current flow. A Modified Three Equation Model has been developed to predict the fate of turbidity currents. Particular attention has focused on the impacts of increased sediment concentration on the field equations and the numerical predictions. Functional relationships for closure hypotheses have been chosen after careful review.; Previous investigations have invoked the dilute suspension approximation for sediment concentrations up to a few percent by volume. Experimentally derived relationships for the effect of sediment concentration on settling velocity show that the dilute suspension approximation is not necessarily valid, even at these low concentrations.; Results show that initial conditions, such as current height, velocity, and sediment concentration, have a short-lived effect on model predictions. Channel properties, such as slope and bed friction, control the long-term evolution of turbidity currents. The Modified Three Equation Model is highly sensitive to the closure relationships. Properties of the fluid-sediment mixture, such as kinematic viscosity and sediment grain size, can lead to predictions of contrary fates for turbidity currents.; In application to Scripps Submarine Canyon, the Modified Three Equation Model predicts a turbidity current with a smaller acceleration than the current predicted by the Parker Three Equation Model.; Turbidity current flow is most sensitive to the sediment entrainment function. The steep nature of this function leads to extreme changes in the predicted sediment entrainment rate for minor changes in the input parameters. Unfortunately, these input parameters include the settling velocity and the shear velocity, two properties of the fluid mixture that are difficult to ascertain with a high level of accuracy. Continued effort needs to focus on this relationship.; The Modified Three Equation Model does not account for shear at the upper interface of the turbidity current. This needs to be addressed. Future laboratory investigations could also provide much needed data against which to test formulations for sediment entrainment, near-bed sediment concentration, and water entrainment, and the effects of ambient currents on turbidity currents.