Headcut erosion characteristics revealed through simulated rainfall and scouring experiments in the gully region of the Loess Plateau

Headcut erosion is the main sediment source that may cause severe damage to the ecological environment and agricultural production. The study of headcut erosion characteristics, such as gully headcut morphological evolution and sediment particle transport processes, is essential for understanding the mechanism of gully erosion. A series of simulated rainfall combined scouring experiments with constant rainfall intensity (0.8 mm min^–1) and variable flow discharge (3.6, 4.8, 6.0, and 7.2 m³ h^–1) were conducted to illustrate the headcut erosion process in the gully region of the Loess Plateau. The results showed that gully width and gully depth increased as time and flow discharge increased. The headcut retreat length increased exponentially with experiment time. The gully head heights decreased by 10, 13, 21, and 26 cm at different flow discharges after 180 min. The contents of clay and silt in eroded sediment particles decreased by 7.97% to 16.59% and 7.98% to 15.34%, respectively, whereas the sand volume fraction increased by 9.33% to 20.04% compared to that of the original soil. The enrichment rates of clay and silt sediment were 0.83 to 0.92 and 0.85 to 0.92, while the enrichment rate of sand sediment was 1.09 under different flow discharges. The critical particle size was 0.0326 mm. The fractal dimension of the eroded sediment particles was 2.61 to 2.67 and showed good agreement with the clay volume fraction, with a coefficient of determination (R²) of 0.93. These results provide a basis for headcut erosion model establishment, ecological management, and soil and water conservation in the gully region of the Loess Plateau.