3-D DIRECT SIMULATION OF DRIFTWOOD ACCUMULATION IN A REAL RIVER FLOOD

Severe damage from river flooding carrying driftwood has become a critical problem. We have developed a code for 3-D simulations of water flows carrying a lot of driftwood by using the cumulant lattice Boltzmann method (LBM) coupled with the discrete element method (DEM). Adaptive mesh refinement (AMR) makes it possible to apply the code to large areas with a high-resolution mesh, and a GPU implementation greatly accelerates the computation. A small-scale water-tank experiment with a driftwood model showed that the computational results were in good agreement with the experiment results. For an actual river-flooding disaster that occurred on the Omoto River in Iwate Prefecture, Japan, we conducted two large-scale computations of large areas with a total of 1000 pieces of driftwood and a maximum resolution of 7.8125 [cm]. The simulation results identified three driftwood accumulation processes: trapping in narrow channels, hitting building corners, and stagnation in front of buildings.