Computationally efficient modeling of hydro-sediment-morphodynamic processes using a hybrid local time step/global maximum time step

A hybrid local time step/global maximum time step (LTS/GMaTS) method is proposed for computationally efficient modeling of hydro-sediment-morphodynamic processes. The governing equations are numerically solved on unstructured triangular meshes using a well-balanced shock-capturing finite volume method with the HLLC approximate Riemann solver. High computational efficiency is achieved by implementing the LTS to solve equations governing sediment-laden flows (i.e., the hydro-sediment part), and implementing the GMaTS to solve equations governing bed materials (i.e., the morphodynamic part). Two benchmark experimental dam-break flows over erodible beds and one field case of the Taipingkou waterway, Middle Yangtze River, are simulated to demonstrate the high computational efficiency and the satisfactory quantitative accuracy. It is shown that the computational efficiency of the new model can be faster by an order of magnitude than a traditional model of similar type but implementing the global minimum time step (GMiTS). The satisfactory quantitative accuracy of the new model for the present cases is demonstrated by the negligible L-2 norms of water level and bed elevation between the new model and the traditional model, as compared to the L-2 norms between the traditional model and the measured data.