Effect of Raindrop Impact on Homogeneity of Sediments in Rill Erosion of Soils with Different Textures

Rill erosion is one of the most important types of water erosion in semiarid dry land areas. The importance of this study is more in the soils of semi-arid regions, similar to many parts of Iran, which have unstable soil aggregates. The aim of this study was to investigate the role of raindrop impact on the size distribution and homogeneity of sediment particles in rill erosion of soils with different textures. Therefore, the effect of raindrops on changes in the size distribution of sediment particles was determined in rills of 4 meters in length and 0.10 meters in width under rainfall simulated with a constant intensity of 90 mm h-1 in different slope gradients (5%, 10%, 15%, and 20%) in 12 soil texture classes. Experiments were carried out in two soil surface coverconditions including with raindrop impact (bare soil) and without raindrop impact (use plastic net), and the effect of raindrop impact on the variables was determined. The experiment was conducted in four replicates with a total of 352 experimental units. The study of this subject using the particle size distribution curve showed that there was a clear difference between the curves in the two soil surface cover conditions. The sediment particles size distribution curves were below the original soil particles size distribution curve, suggesting an increase in the mean diameter of the particles in sediments and an increase in the transport of coarse particles such as sand at the end of the experiment. The increase in geometric standard deviation in the sediment was strongly dependent on soil texture and slope and, contrary to the expected, homogeneity of sediment particles was not significantly affected by the removal of raindrop impact, and by increasing the slope in all soil texture classes, sediment particles heterogeneityincreased, likely due to increase in flow velocity and flow power. The highest non-homogeneity of sediment particles was observed after precipitation in silty soil.