Shallow sediment transport flow computation using time-varying sediment adaptation length

Based on the common approach, the adaptation length in sediment transport is normally estimated astemporally independent. However, this approach might not be theoretically justified as the process of reaching the sediment transport equilibrium stage is affected by the flow conditions in time, especially for fast moving flows, such as scour-hole developing flows. In this study, the two-dimensional (2D) shallow water formulation together with a sediment continuity-concentration (SCC) model were applied to flow with mobile sediment boundary. A time-varying approach was proposed to determine the sediment transport adaptation length to simulate the sediment erosion-deposition rate. The proposed computational model was based on the Finite Volume (FV) method. The Monotone Upwind Scheme of Conservative Laws (MUSCL)-Hancock scheme was used with the Harten Lax van Leer-contact (HLLC) approximate Riemann solver to discretize the FV model. In the flow applications of this paper, a highly discontinuous dam-break, fast sediment transport flow was used to calibrate the proposed time-varying sediment adaptation length model. Then the calibrated model was further applied to two separate experimental sediment transport flow applications documented in the literature, i.e. a highly concentrated sediment transport flow in a wide alluvial channel and a sediment aggradation flow. Good agreement with the experimental data were obtained with the proposed model simulations. The tests prove that the proposed model, which was calibrated by the discontinuous dam-break bed scouring flow, also performed well to represent rapid bed change and steady sediment mobility conditions.