Effects of rainfall intensity and topography on rill development and rill characteristics on loessial hillslopes in China

Abstract

Rill development is a major soil erosion process that causes severe soil degradation. This study examined the effects of representative rainfall intensities (50 and 75 mm h−1), slope gradients (10° and 15°), and slope lengths (7.5 and 10.0 m) on rill development and rill characteristics on loessial hillslopes in China. Loessial soil was collected from the cropland of Ansai Town, Yan’an City, Shaanxi Province. The soil with 28.3% sand, 58.1% silt, and 13.6% clay was packed into a soil pan to conduct rainfall simulations in 2012. The results showed that the time of the knickpoint occurrence (5–16 min), the rill headcut extension (9–33 min), and the mean headward erosion rate (1.7–5.0 cm min–1) were better representative indicators for reflecting the changes in the rill development than other indicators used in this study. For a quick evaluation of the rill erosion severity, the rill coverage ratio (1%–12%, generally increasing with an increase in the rainfall intensity) was better than the other indicators for treatments with different rainfall intensities, and the rill width-depth ratio (1.56–2.27, generally decreasing with an increase in the slope gradient) was better than the other indicators for treatments with different slope gradients. Furthermore, the rill inclination angle (8.2°–19.1°, significantly increasing with an increase in the slope length) and rill density (0.19–1.34 m · m−2, generally increasing with an increase in the slope length) were more suitable for evaluating the rill erosion severity on hillslopes with different slope lengths. Therefore, the representative indicators could reflect the differences in the rill development and rill characteristics under different rainfall and topographic situations. The study greatly improved the evaluation of rill erosion severity and the prediction of the development of rills for loessial hillslopes.