Effect of rock fragment content on erosion processes of disturbed soil accumulation under field scouring conditions

PURPOSE: Soil and water erosion from high rock fragment content disturbed soil accumulation severely threatens ecological security. Evaluation of the quantitative influence of rock fragment content on soil erosion processes was the basic research for soil and water conservation. MATERIALS AND METHODS: Field simulation scouring experiments were conducted on the disturbed soil accumulation experimental plot. A 10 × 1-m² plot with 28 gradients was established on Changwu Experimental Station in the Loess Plateau, China. Tap water was applied at the top of the plot with the four different flow discharge rates of 1.3 × 10⁻⁴, 1.7 × 10⁻⁴, 2.1 × 10⁻⁴ and 2.5 × 10⁻⁴ m³ s⁻¹ to simulate surface runoff processes. The experimental plots underlying surfaces were filled with different rock fragment content of 20%, 40% and 0%. The soil used in these experimental plots was a silty loam from the disturbed soil accumulation formed by expressway construction in the loess plateau areas. The disturbed soil accumulation site was located near the G70 Fujian–Yinchuan expressway and the vegetation cover was very low. The mean diameter of rock fragments was 22 mm in these experiments, and the rock fragments were unsmooth, angular crushed stone taken from the quarry in the Changwu County. RESULTS AND DISCUSSION: The results showed that rock fragment content of 20% and 40% could significantly decreased runoff and sediment (P < 0.05), although there was no significantly different between 20 and 40%. The rock fragments decreased mean flow velocity by 43 to 55% in mean flow velocity compared to the pure soil. Furthermore, the flow was laminar flow in the rock fragments slope. The rock fragments significantly decreased flow shear stress (52–89%), stream power (63–89%), unit stream power (41–59%), runoff kinetic energy (67–88%) and unit energy of the water-carrying section (81–89%) compared with the pure soil. With increased rock fragment content, the rill erodibility decreased. The rill erodibility was estimated to be 1.4 × 10⁻³ s m⁻¹, 0.7 × 10⁻³ s m⁻¹ and 0.5 × 10⁻³ s m⁻¹, under the condition of pure soil, rock fragment content of 20% and 40%, respectively. CONCLUSIONS: Low rock fragment content (< 40%) in disturbed soil accumulation significantly decreased runoff and sediment. With the rock fragment content increased, the rill erodibility was decreased. Appropriate rock fragment content could be used to control soil erosion on disturbed soil accumulation in practice. The important parameters from this study will be helpful for disturbed soil accumulation erosion prediction model establishment.