New drag force model for dam-break flows through vegetation under non-hydrostatic conditions and its comparison with high-resolution, fully-resolved model

Abstract

The effects of vegetation on dam-break flows have been studied only occasionally, often using the conventional drag force formula, which is inadequate for modeling non-uniform flows around emergent obstacles. Therefore, further investigation into drag force formulations is crucial. This study validates numerical simulations against experimental data of dam-break flows through emergent vegetation. In the laboratory, vegetation was modeled as emergent cylinders with various configurations under different initial Froude numbers. Two types of numerical simulations were conducted: (1) fully-resolved modeling using fine-resolution meshes to treat cylinders as wall boundaries, and (2) modeling cylinders as a density value in the drag force formulation. The latter approach introduced a novel drag force formula for non-equilibrium conditions, considering the base drag force component, water surface variations, and pressure gradient, integrated into a semi-implicit computation with the bed friction term evaluated using the Manning formula. Using coarser meshes than the fully-resolved modeling, the proposed approach proved appropriate for quantifying drag force with relatively small errors of less than 10 % against experimental data, while being approximately 690 times less computationally demanding. All non-hydrostatic simulations incurred computational costs up to three times greater than those computed under the hydrostatic assumption alone.