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| Purpose: This study aimed to (1) observe the effects of rock fragment content on slope erosion processes and eroded sediment selectivity; (2) acquire the effective and ultimate particle size distributions (PSDs) of sediments from slope erosion; and (3) elucidate the influencing factors and characteristics of eroded sediment particles.
Materials and methods: The test soil used in this study was collected from Beibei, Xiema in Chongqing, China. We collected six separate soil samples with 0%, 5%, 10%, 20%, 30%, and 40% rock fragments. The experiment were conducted on two parallel 5 m × 1 m × 0.4 m troughs. The rainfall simulation experiments were performed in the State Key Laboratory of Soil Erosion and Dryland Farming in the Loess Plateau. After rainfall, we measured the sediment PSDs using MasterSizer 2000. The PSD data obtained after the sediment was fully dispersed into primary particles labeled the ultimate PSD; whereas those obtained without any dispersion treatment was labeled the effective PSD.
Results and discussion: Results revealed that eroded sediment selectivity was represented by clay enrichment. The effective/ultimate ratio of the clay-sized sediments was <1, and this ratio increased as rock fragment contents increased. Silt-sized particles were transported mainly as primary particles because the effective/ultimate ratios of silt-sized particles were closer to 1 than other ratios. The enrichment ratios of sand-sized particles decreased from 0.79 to 0.55 as rock fragment contents increased. The effective/ultimate ratios of sand-sized particles were >1, and this finding suggested that most sand particles, especially those with low rock fragment contents, eroded as aggregates. Clay-, silt-, and sand-sized sediment aggregates were significantly correlated with sediment yield, rock fragment content, and runoff yield strength.
Conclusions: The results showed that the runoff coefficient consistently increased as rock fragment contents increased. The soil loss ratio (SLR) and the erosion rate reduced as rock fragment content increased. The relationship between SLR and rock fragment content can be described well in terms of quadratic function. The silt-sized particles were transported mainly as primary particles. The clay-, silt-, and sand-sized sediment aggregates were significantly correlated with rock fragment content. |
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| Keywords:Effective/ultimate ratio; Enrichment ratio; Eroded sediment particles; Particle size distribution; Rock fragment; Soil loss ratio |
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