3D numerical model of sediment transport considering transition from bed-load motion to suspension : application to local scours upstream of cross-river structures

Kazuyuki Ota, Takahiro Sato, Hajime Nakagawa

Tuesday 30 june 2015

14:05 - 14:20h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 6A. Sediment - Erosion

In upstream region of a cross-river structure with an opening (e.g. check dam), a crater-shaped scour hole forms. One of the features of this scour phenomenon is that the bed load motion in the longitudinal direction is interrupted by the cross-river structure, and the bed load is entrained into suspension by contracted flow into an opening of the structure. In order to simulate such a scour phenomenon, this work develops a novel 3D numerical model of flow and sediment transport, which considers the nonequilibrium of sediment transport including transition process from bed load into suspension. The numerical model for fluid solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Volume of Fluid (VOF) method and k-_ SST turbulence closure model. The temporal change in bed topography is calculated by coupling a momentum equation of sediment particles and stochastic model for sediment pick-up, deposition, and transition from bed load motion to suspension. To validate the numerical model, we applied the model to a scour experiment using a slit weir in a rectangular flume with 0.5m width and 0.35m height. In the experiment, the bed particle was entrained into suspension and crater-shaped scour holes formed at upstream of the slit weir. A comparison between the numerical and experimental results indicated that the model can reproduce the temporal variation of scour geometry upstream of a cross-river structure with sufficient accuracy. Also, the transition from bed load motion into suspension was found to be important to explain the local scour upstream of a cross-river structure.