Numerical investigation on the role of check dams with bottom outlets in debris flow mobility by 2D SPH.

Check dams with bottom outlets are widely used in debris flow gullies to minimize the damage caused by debris flows. However, the bottom size is often based on empirical criteria due to the lack of knowledge of the interaction between the debris flow and the check dam with the bottom outlet. In this study, the interaction between a viscous debris flow and check dams with bottom outlets is investigated via flume tests using 2D smoothed particle hydrodynamics. The normalized height of the bottom outlet is varied from 0 to 1, and slope angles from 15 to 35° are considered. Based on the numerical results, the jump height decays with the increasing normalized height of the bottom outlet and this trend can be approximated by a power law function. When the normalized height of the bottom outlet is less than 0.15, the performance is similar to that of a closed check dam. The flow regulation and sediment trapping functions of the check dam may fail when the normalized height of the bottom outlet is greater than 0.6. These results show that the energy breaking, flow regulation, and sediment trapping functions of check dams with bottom outlets operate well when the normalized height of the bottom outlet is in the range 0.15-0.6. Even if model limitations require further efforts to validate the findings of this study, they provide a basis for the rational design of check dams with bottom outlets.