Variability of hydraulic characteristics of sediment-laden rill flow under various slopes, water flows and sediment loads

During soil erosion, sediment load of rill flow changes dynamically and may affect its hydraulic characteristics. However, current research on hydraulics of sediment-laden rill flow primarily uses river sand/artificial homogeneous materials as sediment, which significantly differ from natural soil, leaving a research gap on how soil quantity impacts rill flow hydraulics. This study uses natural soil in an indoor rill flume simulation experiment to explore how sediment load influences hydraulic characteristics of rill flow, including flow velocity (V), Darcy–Weisbach friction coefficient (f), Reynolds number (Re), Froude number (Fr), and flow depth (h). Experiments were conducted under combinations of six different sediment loads, five flow discharges, and five slopes. The results indicated that V, f, Re, Fr were significantly influenced by sediment concentration. V and Fr show an upward trend as the sediment load increases, while f, Re, and h demonstrate a downward trend. The sediment load predominantly influences V, f, and Fr, accounting for contributions of 0.33, 0.49, and 0.39, respectively. The influence of slope gradient on V and Fr intensifies as the sediment load increases, while the impact of flowdischarge on V, f, and Fr diminishes. As flow discharge increases, the effect of sediment load diminishes on V and Fr, and that of slope gradient strengthens. Two kinds of prediction equations were developed for estimating thehydraulic parameters of sediment-laden rill flow. The models demonstrate high R2 values (0.74 to 0.98), suggesting strong performance of the prediction equations. These findings lay a foundation for the better development of a physical process-based rill erosion model. Given the differences in the properties of natural soils,which may impact hydraulic characteristics, it is a limitation of this study that it only focuses on a single soil type, and thus future research should explore the effect of sediment properties on hydraulic characteristics.