A trapping capacity constraint model for sediment transport in vegetative filter strips (VFS) on sloping surfaces

Most current modelling practices for sediment trapping in vegetative filter strips (VFS) assumed a constant sediment trapping efficiency of VFS, while, in practice, it was found to decrease greatly with the increasing trapped sediment amount in VFS (decreasing sediment trapping capacity of VFS). To account for this impact, a widely used VFS sediment transport module was modified to consider the changing sediment trapping capacity of VFS, which was expressed by a power-law relationship with the inflow discharge, sediment concentration, slope gradient, and antecedent deposition amount. An integrated model that coupled a slope infiltration-runoff module and the modified sediment transport module was then developed to simulate hydrology and suspended sediment transport in VFS on sloping surface. The model is calibrated and validated by 18 VFS experiments with different inflow, sediment, and slope conditions from Luo et al. (Science of the Total Environment, 725, 138361, 2020). Good agreements between observed and simulated runoff and sediment transport processes were found for nearly all cases. Due to the impact of changing sediment trapping capacity of VFS, the trapped sediment amount and the sediment transport rate of outflow varies greatly in space and time. With the increase of inflow discharge, sediment concentration, and slope gradient, the overall sediment trapping efficiency of VFS tends to decrease greatly and then remains almost unchanged. The comparison between proposed model and original physically based model shows that neglecting the impacts of changing sediment trapping capacity of VFS would lead to a constant and overly large sediment trapping efficiency of VFS, especially on steep slopes. Moreover, comparing with the empirical expression, the model with well-founded theory can provide higher fidelity and more detailed results. Thus, the modelling framework is expected to provide a more effective approach for VFS assessment and maintenance in local or watershed scale.