Author(s): Yan Xiong; Qiuhua Liang; Xue Tong; Jinhai Zheng; Gang Wang
Linked Author(s): Yan Xiong, Qiuhua Liang, Xue Tong, Jinhai Zheng, gang wang
Keywords: Shallow water equations; Discrete element model; Coupled model; Flash flooding; Floating debris
Abstract: Flash flooding is one of the most devastating natural hazards in the world, worsened by climate change and urbanization. As evidenced from some of the recorded footages of recent catastrophic flash flood events, floating debris may block bridges, damage structures, alter flood pathways and exaggerate impact. However, limited study has been conducted on understanding and modelling the dynamics of floating debris and their impact on flooding processes at a large spatial scale. In this work, a new fully coupled modelling approach is developed for simulating debris transport initiated and driven by flash floods, based on a finite volume shock-capturing hydrodynamic model solving the 2D shallow water equations (SWEs) and a 3D discrete element model (DEM). The proposed two-way coupling approach estimates the hydrostatic and dynamic forces acting on floating objects using the high-resolution water depth and velocity predicted by the hydrodynamic model; the corresponding counter forces on the fluid are then taken into account by adding extra source terms in the governing equations of the hydrodynamic model. The proposed modelling strategy overcomes the limitation of most existing approaches that rely on calibrated empirical parameters to estimate forces. The DEM model is further incorporated with a multi-sphere method (MSM) to better represent actual shape of floating objects, such as vehicles or trash bins. The new coupled model is computationally accelerated by implementation on modern GPUs to achieve high-performance computing. The numerical model is first validated against a dam-break flume experiment in which the debris transport is interacted by two fixed obstacles. The movements of three floating objects in both horizontal and vertical directions are investigated. The numerical results, in terms of water depth and floating object displacements, compare well with the experimental observations. The coupled model is then applied to reproduce the interactive transport process of floating vehicles during the flash flood in Boscastle, UK, in 2004. During the event, 116 vehicles were washed away and blocked two bridges downstream, causing the river to surge out of the bank and flow onto surrounding streets in the town. The current model well predicts the flood paths and transport and final locations of floating vehicles. Successful reproduction of the Boscastle event demonstrate that the proposed coupled model provides a robust and innovative approach for simulating large-scale flash flooding processes, including debris transport.