Experimental Determination of Sediment Transport Capacity of Concentrated Water Flow over Saturated Soil Slope

Sediment transport capacity (STC) is an important variable for characterising soil erosion on hillslopes. STC also determines the capability of sediment delivery and solute transportation. An experimental methodological strategy was developed in this study to measure the STC in eroding rills on a saturated soil slope. The STC was ensured by using a slope‐raised flume section to feed sufficient amounts of sediments into the water flow, and a flume section was used to stabilize the water flow and produce sediment concentration at the STC level for measurement. Experiments under four slope gradients of 5°, 10°, 15° and 20° and three unit‐width flow rates of 0.33, 0.67 and 1.33 × 10⁻³ m³ s⁻¹ m⁻¹ were conducted to measure the STCs on saturated soil slopes, with the experiments on STCs on non‐saturated soil slopes as control treatments. The measured STCs range from 0.16 to 1.41 kg s⁻¹ m⁻¹ over the saturated loess slopes. The STC measurement method for saturated soil slopes was verified as feasible by the small SDs of the measured STCs and the agreement between the trend of rill sediment delivery rate and the STC values at the slope gradient of 20° and three unit‐width discharges. The relationships between STC and slope gradient and those between STC and unit‐width flow rate over saturated soil slopes matched well with the power and linear functions, respectively. Furthermore, the STC values correlated well with the flow velocity. The STC value on the saturated loess slope was approximately 25% larger than that on the non‐saturated loess slope. An empirical power function of slope gradient and unit‐width flow rate was found to predict the STC on saturated loess slopes effectively. Therefore, the measurement method for soil erosion from saturated soil slopes can help to estimate the STC and obtain key parameters for the soil erosion prediction model. HIGHLIGHTS: The sediment feeding by slope‐raised flume section was used to measure sediment transport capacity (STC) of saturated soil slope, and its feasibility was tested. The STC value over the saturated soil slope was significantly greater than that over non‐saturated soil slope. The STC over the saturated soil slope could be empirically expressed as the product of power functions of water flow rate and slope gradient.