Erosion vulnerability of sandy clay loam soil in Southwest China: Modeling soil detachment capacity by flume simulation

Soil detachment capacity (Dc) is a key parameter in many soil erosion models and is typically estimated using hydraulic parameters. However, the accuracy of predicting Dc and its relationship to hydraulic characteristics remains poorly understood for many soil types. This study investigates the predictability of Dc with hydraulics by simulated scour rill flow and quantifies erosion vulnerability to rill erosion as reflected by rill erodibility and critical hydraulic values for an Entisol from Southwestern China. Small samples (10 cm in diameter, 6 cm in depth) of sandy clay loam of Entisol were subjected to scouring by simulated rill flow under the combinations of flow discharges (18.8, 26.3, 46.6, 54.4, 64.61 min(-1)) and slope gradients (3.5%, 8.7%, 17.6%, 26.8% and 36.4%). The results showed that Dc increased as a power function with flow discharge irrespective of slope gradients, and at low discharge gradients Dc increased as a power function with slope and with transitions to a linear function at higher discharge gradients. The association of flow discharges and slope gradients was a better predictor of Dc than flow depths and slope gradients. Shear stress and stream power were similar and better predictors of Dc than flow velocity, unit stream power and unit energy. Rill erodibility related to all hydraulic parameters were significantly different from zero under combination of flow discharges and slope gradients, and this was true for critical hydraulic values related to comprehensive data. Relatively higher rill erodibility and lower critical hydraulic values compared with other soils demonstrated that sandy clay loam of Entisol is susceptible to detachment. These results highlight the erosion vulnerability of Entisols and provide deeper insights on the reliability of hydraulic parameters which strongly affect soil detachment modeling.