Effects of rainfall intensity and slope gradient on erosion characteristics of the red soil slope

Soil erosion is one of the most serious driving forces of ecosystem degradation in the world that strongly affected by rainfall intensity and slope gradient. Therefore, a laboratory simulated rainfall study, with three slope gradients (5°, 15°, and 25°) subjected to seven rainfall intensities (30, 60, 90, 120, 180, 210, and 270 mm/h), was conducted to determine the effect of rainfall intensity and slope gradient on runoff generation, rate, sediment yielding, erosion rate, and runoff hydraulics characteristics of the red soil slope. The results indicated that runoff generation of red soil slopes was influenced by both the slope angle and rainfall intensity, runoff rate showed a steady condition after an initial trend of an unsteadily increased with increasing rainfall duration, while it did not increase with the increasing slope gradients, especially under the high rainfall intensity. Under the influence of high rainfall intensities, sediment yielding of the red soil slope was controlled by detachment limitation and then by transport limitation under low rainfall intensity. Under low and moderate rainfall intensities, erosion rate increased with slope angle due to the factors related to slope angle can enhance soil detachment or limit the protective effect of surface layer. Furthermore, runoff hydraulic characteristics of the red soil slope indicating that overland flows on all slopes were considered as laminar, tranquil, and supercritical, and the Reynolds numbers were significantly correlated with rainfall intensity. Results from this study can expand the understanding of the relationship among slope gradient, rainfall intensity, and erosion characteristics in the red soil region.