One-dimensional coupled model for predicting turbidity currents in reservoirs

Among traditional depth-averaged models for predicting turbidity currents, it is difficult to take into account the influence of flow and sediment conditions at the plunge point and the gradient of free water surface. Therefore, a one-dimensional unsteady turbidity current model for reservoirs with irregular cross-sections is proposed, and a two-step calculation mode of alternating the calculations of turbidity current and open channel flow is adopted in this model. The proposed calculation mode can dynamically determine the location of the upstream boundary for the turbidity current simulations using the plunge criterion, and can also connect the reach transported in the pattern of open channel flow and the reach transported in the pattern of turbidity current. Three processes of flow movement, sediment transport and bed evolution in a reservoir are solved by a fully coupled approach, with a TVD (Total Variation Diminishing) version of the MUSCL-Hancock scheme being used in this solution. Turbidity current movements in two laboratory experiments were simulated under different setups, including an instantaneous fixed-volume release and a constant-flux input, with the effect of free surface gradient on the model predictions being investigated. The calculations indicate that the proposed model can satisfactorily predict the thickness and sediment concentration of turbidity currents and their propagation processes, which can be used as a tool for the sediment management in reservoirs.