Determination of sediment transport capacity by hydrodynamic variables considering subsurface water flow

Abstract Subsurface water flow can cause serious soil erosion on sloping farmland. Sediment transport capacity ( T c ) data at different subsurface water flow depths are limited. The objective of this study was to develop a new equation that can accurately determine T c under subsurface water flow impacts. Subsurface water flows were arranged at three depths: 15, 10, and 5 cm. Three flow discharges (2, 4, and 8 L min −1 ) and four slope gradients (5°, 10°, 15°, and 20°) were designed to conduct flume scouring experiments. The results indicate that flow velocity, shear stress, and unit energy with linear equations and stream power with power equations can be used to determine T c , but those using the unit stream power perform relatively poorly under the different subsurface water flow depths. Among these parameters, the shear stress is the preferred predictor of T c . The addition of prediction parameters, subsurface water flow depth, in response to T c equations can improve the accuracy of T c modeling. The power‐exponential equation of shear stress combined with the subsurface water flow depth best described the T c of rill flow under subsurface water flow impacts. Subsurface water flow can increase the soil erodibility, and thus decrease the critical shear stress, resulting in a lower critical flow velocity at which sediment transport capacity can be achieved. This research provides a new equation for directly determining T c in subsurface water flow‐impacted rill flow on purple soil slopes.