Experimental study of sediment transport processes and size selectivity of eroded sediment on steep Pisha sandstone slopes

Abstract

The Pisha sandstone area on the Ordos Plateau of China is the primary source of coarse sediment (with a particle size d > 0.05 mm) of the Yellow River. Sediment size distribution and selectivity greatly affect sediment transport and deposition. Hence, sediment transport processes and size selectivity by overland flow on Pisha sandstone slopes were investigated in this study. Experiments were run with Pisha sandstone soil (bulk density of 1.35 g cm−3) under rainfall intensities of 87 and 133 mm h−1 with a 25° slope gradient, and the duration of simulated rainfall was 1 h. Sediment and runoff were sampled at 2-min intervals to examine the size distribution change of the eroded sediment. The particle composition, enrichment rate, fractal dimension, and time distribution characteristics of median grain size (d50) of eroded sediment were comprehensively analyzed. Statistical analyses showed that Pisha sandstone slope generated a large amount of coarse sediment during the erosion. >40% of eroded sediment particles were coarse sediment, which will become the main sediment in the lower reaches of the Yellow River bed. The particle size of eroded sediment tended to gradually decrease with the continuous rainfall but remained larger than the initial value of Pisha sandstone soil after refinement. The fractal dimension was positively correlated with the slope flow velocity, while the d50 was negatively correlated with the slope flow velocity. Overall, these findings indicates that the selectivity and transportation of sediment particles on the Pisha sandstone slopes is mainly influenced by the hydrodynamic parameters of overland flow. The reason for the large amount of coarse sediment generated during the erosion in Pisha sandstone area is not only related to the large porosity and a small cohesive force of sand, but also related to the hydraulic conditions of the Pisha sandstone slopes. In the Pisha sandstone area, we should control soil erosion mainly by reducing the initial erosion dynamics, such as reducing splash erosion, increasing soil infiltration and surface resistance. This study provides a methodology and data references for studying the particle selectivity characteristics of eroded sediment and provides a scientific basis for revealing the mechanism of erosion and sediment yield in the Pisha sandstone area of China.