Background The distribution of rill erosion is widespread in the Loess Plateau where rill erosion is serious and its morphology is complex. Rill erosion causes soil nutrient loss, farmland area reduction and seriously endangering ecological security. The rill morphology varies under different rainfall and slope conditions, studying the rill morphology parameters may accurately characterize the erosion regulations.

Methods Using artificially simulated rainfall test and three-dimensional laser scanning technology, 90 mm/h rainfall intensities and four slope gradients (5°, 7.5°, 10° and 15°) for test conditions. All data were obtained and analyzed by ArcGIS 10.4 and SPSS 25 software, and Origin 2024 was used for result analysis and graphing.

Results 1) With the increase of slope gradient, the initial flow generation time of slope relatively delayed. Rill erosion stage compared to the sheet erosion stage, the average runoff increased 14%, 47%, 41% and 56%, the average sediment yield increased 3.2, 14.5, 7.5 and 17.8 times respectively, the rill morphology development was dominated by head-to-head erosion and accompanied by severe collapse. 2) The width and depth of a rill fluctuated widely, the ratio of rill width to depth presented a decreasing trend in general, the rill surface area, rill volume and average cross-sectional area were 15° > 7.5° > 10° > 5°. 3) After the completion of rill development, the contour deviation increased significantly at 4-10 m in location, the surface roughness mainly increased in the middle and lower slope, and slope surface roughness was closely related to the complexity of the rill. 4) There was a significant positive correlation between total sediment yield and rill volume, the total runoff of the slope had a significant positive correlation with the average width to depth ratio of rill.

Conclusions The rill is widely distributed on the Loess Plateau, and rill morphological characteristics are complex in different regions, so selecting appropriate morphological parameters is of great important for quantitatively characterizing rill erosion. The results and tests method may provide some theoretical supports for quantitative study of rill erosion and ecological protection.