Numerical model of local scour considering the unsteady sediment inflow and sediment sorting: Application to scour upstream of slit weir

The current study proposes a novel framework for the numerical model for estimating the temporal scour considering unsteady sediment inflow and the sediment sorting process. The framework was applied to local scour upstream of a slit weir. The scour model is based on an ordinary nonlinear differential equation derived from sediment continuity and scour rate equations. A one-dimensional (1-D) Boussinesq-type model coupled with nonequilibrium sediment transport was incorporated in the scour model to consider unsteady sediment inflow. In addition, a mixing layer approach was incorporated to determine temporal variations in particle size in the scour hole. The proposed framework was validated using scour experiments conducted under conditions that include non-uniform sediment, live-bed scour, and unsteady flow rate. The simulation results showed satisfactory agreement with experimental results for the scour upstream of a slit weir. The proposed model appropriately explained the hysteresis process for flow unsteadiness, refilling process for live-bed scour, and armoring process for non-uniform sediments. In addition, the model framework proposed in the current study is applicable to local scour around other hydraulic structures (e.g., bridge piers) upon establishing the scour rate equation. Therefore, the current study provides a novel approach for modeling temporal scour that is required to consider unsteady sediment inflow and sediment sorting.