High-fidelity three-phase flow simulation of flash and riverine floods in real-life waterways

Abstract

We present a fully coupled three-phase flow model of air-water-sediment to simulate numerically the propagation of riverine and flash flood events in field-scale waterways. The turbulent flow and free surface of floods are computed using the large-eddy simulation (LES) and level-set method, respectively. The evolution of channel morphology, due to propagating floods on the mobile beds, is calculated using an Eulerian morphodynamics model based on the curvilinear immersed boundary method. We demonstrate the capabilities of our numerical framework by applying it to simulate flash and riverine flood events in kilometer-long reaches of natural waterways in California. The simulated regions of these waterways include a number of bridge foundations. Simulation results of the model for the flash flood event revealed the formation of the highly complex flow field and scour patterns within the waterways. Moreover, our simulations show that most of the scour processes take place during the steady phase of the flash flood. A riverine flood simulation is also conducted using the unsteady Reynold-Averaged Navier-Stokes based (RANS) model to study the impact of the flood flow on the scour process near the bridge foundations.