Numerical simulation of the pit migration

The purpose of this paper is to simulate the migration of a pit in the channel bed. When water flows over a pit, the velocity at the upstream end of the pit slows down rapidly owing to the increment of the flow depth, and that at the downstream end of the pit speeds up because of the sudden contraction of the now area. Under such a flow condition, the equilibrium sediment transport formula is inadequate to simulate the local deposition and scouring around the pit. In addition, the critical bed-shear stress without considering the bed slope effect may increase the deposition rate near the upstream end and the scouring rate near the downstream end of the pit. This paper proposes a numerical model to simulate the migration of a pit by considering the nonequilibrium sediment transport behavior and the modified critical bed-shear stress for the movement of sediment on the large bed slope. The capability of the model was verified by comparing the simulated results with one of the experiments executed by Lee et at. (1993).