Investigating the Intense Sediment Load by Dam-Break Floods Using a Meshless Two-Phase Mathematical Model

Extreme precipitation is increasing the risk of dam breaks and formation occurring debris dams. Accurate prediction of dam-break wave propagation is critical to disaster emergency management. Intense bed-load transport by dam-break floods can result in a dramatic change of topography, which in turn may affect flood propagation. However, only a very few studies have investigated the thin intense bed-load layer under dam-break floods. In this paper, a meshless two-phase mathematical model is utilized to examine the water velocity, sediment velocity and volumetric fraction, and bed-load transport flux as well as energy dissipation in bed-load layer. The model is applied to simulate two- and three-dimensional laboratory experiments of dam-break wave over erodible beds. For the two-dimensional experiment, the relative root mean square errors in computed water surface are all below 3.60% and those in profiles of bed-load layer and static bed are mostly below 13.40%. For the three-dimensional case, the relative error in computed highest water level is lower than 5.9%. Sediment stream-wise velocity in bed-load layer follows a power-law vertical distribution while sediment volumetric fraction decreases linearly upwards. Accordingly, a formulation of the vertical distribution of bed-load transport flux, contradictory to the parabolic law in existing studies, is proposed. Most of the water mechanical energy transferred to the sediment is dissipated due to the shear stress in the intense bed-load layer while only a limit part is kept by the sediment grains. Energy dissipation due to sediment shear stress dominates the consumption of total mechanical energy in the two-phase system.