The Selectivity of Soil Particles in Relation to Flow Characteristics in Rill Erosion

Rill erosion is an important form of water erosion on cultivated slopes. Rills are flow paths that are created by concentrated flow on hillslope and causes higher rates of soil loss. The amount and type of particles transferred through the rills or the selectivity of the particles may be affected by various factors, especially the flow rate. This study was conducted to investigate the rill erosion and the particle selectivity under the flow characteristics. Field experiment was done in a rainfed land with a slope gradient of 10% in the rills/furrows with 6 m in long under different flow intensities (2, 2.5, 3, 3.5 and 4) using a randomized complete block with three replications. Field measurements were performed using a flow rate of 3 lit min-1 at intervals of 5-min for 60 min. Rill erosion and the particle selectivity were determined along with flow characteristics for various flow intensities. Significant correlations were found between flow intensity and flow characteristics (velocity, shear stress and power), rill erosion and the selectivity of particles. With an increase in flow rate, flow characteristics increased in the rills and enhanced rill erosion as well as the selectivity of sand and clay, whereas the selectivity of silt decreased in the rills. Silt showed the highest sensitivity to selection by concentrated flow, so that flows with lower shear stress could erode it from the rills. Wholly, this study revealed that the flow rate is the most flow characteristics influencing rill erosion and the selectivity of soil particles.