Size sorting in rill detachment for a typical silt loam on the Loess Plateau

Abstract

Soil detachment is the initial subprocess of soil erosion, and provides sediment for subsequent sediment transport and deposition. Understanding the size sorting mechanisms during soil detachment is crucial for advancing our knowledge of soil erosion. To investigate these mechanisms, a typical silt loam from the Loess Plateau was selected, and PVC rill flume tests (3 m × 0.1 m × 0.05 m) were conducted at four slopes (9°, 12°, 15°, and 18°) and five flow discharges (3, 5, 7, 9, and 11 L min⁻¹). The results indicated that the effective median particle size (D₅₀) of the detached sediment was smaller than that of the original soil, whereas the ultimate value was larger. The effective D₅₀ decreased with increasing slope but exhibited an initial increase followed by a decrease as the flow discharge increased. The sediment primarily consisted of effective fine and coarse silt, with a higher content of effective fine silt than the original soil. Under the experimental conditions, a flow discharge of 7 L min⁻¹ was identified as the critical point at which the influence of the flow discharge on the selectivity of effective particles began to stabilize. During rill detachment, most fine or medium-to-coarse sand particles were agglomerated by clay and fine silt particles. Particles smaller than 21.66 μm or larger than 119.38 μm were prone to detachment. These findings could enhance the understanding of sorting mechanisms during rill detachment, and provide a theoretical basis for preventing and mitigating of soil erosion on the Loess Plateau.