ABSTRACT Graphical abstract showing the comparison of measured and WEPP-predicted rill erodibility (Kr) and critical shear stress (τcr) for sandy loam and clay loam soils under four slope gradients (3%, 5%, 7%, and 10%). The figure includes bar charts presenting measured and predicted parameter values with error bars, together with a table summarizing mean values and statistical group comparisons among slope treatments and soil types. Understanding the detachment process in small channels is essential for improving process-based erosion modelling. However, the reliability of rill parameters in the Water Erosion Prediction Project (WEPP) model across slopes and soil textures remains insufficiently evaluated. This study hypothesizes that slope and texture control rill detachment thresholds and that model predictions may be biased under saturated conditions. Mini-flume experiments were conducted using sandy loam and clay loam soils under saturated conditions to isolate slope and soil texture effects. Four slope gradients (3, 5, 7, and 10%) were tested, and detachment parameters were derived from runoff and sediment data. Results showed erodibility (Kr) was higher in clay loam, while critical shear stress (τcr) increased with slope in both soils. Slope exerted a statistically dominant control (Kr: F = 53.74; τcr: F = 41.77, p 0.001), whereas soil texture played a secondary role. Kr decreased with slope (0.0199–0.0043 and 0.0639–0.0072 s m−1), while τcr increased (0.56–0.86 Pa and 0.45–0.90 Pa). WEPP predictions showed reasonable agreement for sandy loam but lower accuracy for clay loam. Although based on controlled mini-flume experiments with repacked soils that do not fully represent natural hillslope conditions, the results help refine rill detachment parameters and erosion thresholds.
AKSOUH et al. (Sat,) studied this question.