紫色土坡面细沟侵蚀过程中泥沙颗粒特性

Characteristics of sediment particles during rill erosion on purple soil slope

为探究侵蚀泥沙粒径分布及分选特征,更好地理解紫色土坡面泥沙分离、输移和沉积过程,该研究以西南地区典型紫色土为研究对象,通过室内放水冲刷试验,开展了不同流量条件下10°和15°坡面细沟侵蚀过程以及泥沙颗粒变化特征研究。结果表明:1)各坡面产流率、产沙率均随冲刷流量的增加而增大,当冲刷流量从4 L/min增加至8 L/min,坡面平均产流率增加了1.35~2.37、1.70~1.97倍,坡面平均产沙率增加了1.31~3.51、7.70~8.58倍,产沙率受坡度影响高于产流率。2)各坡面侵蚀泥沙中粉粒占比最高,介于47%~55%。黏粒的富集率(Enrichment Ratio,ER)<1,团聚率(Aggregation Ratio,AR)>1,表明该粒级的泥沙颗粒在侵蚀过程中发生了损耗,并以团聚体的形式迁移;粉粒的ER>1,AR≈1,表明该粒级的泥沙颗粒发生了富集,并且大部分颗粒以单粒方式被运移。各坡面黏粒与粉粒富集率随流量增加而增大,且在高流量下,细颗粒更易富集。3)体积分形维数变化范围为2.43~2.63。各坡面随着冲刷时间的持续,体积分形维数呈现降低的趋势,且分形维数与黏粒含量、粉粒含量呈极显著正相关关系(P<0.01),与砂粒含量呈极显著负相关关系(P<0.01)。该研究结果有助于阐明坡面侵蚀过程中泥沙粒径的变化规律,可为指纹因子的粒径选择及揭示紫色土坡面流失机理提供数据支撑和理论依据。

Studies of sediment particle distribution and sorting properties at different gradations can reveal hillslope soil erosion mechanisms and better understand the processes of sediment detachment,transport,and deposition on purple soil slopes.In this study,the research object selected was the typical purple soil in southwest China.The indoor water flushing experiments were carried out on the purple soil slopes,with two types of slope gradients:10°and 15°,and three types of flow discharge conditions:4,6,and 8 L/min.The rill erosion processes as well as the various characteristics of sediment particles on the slope were thoroughly investigated.The results showed that:1)the runoff rate and sediment yield rate of 10°and 15°slopes both increased with the increase of flow discharge conditions.Under 6 L/min and 8 L/min flow discharge conditions,the average runoff rate of each slope increased by 1.35-2.37 and 1.70-1.97 times,respectively,compared to the flow discharge condition of 4 L/min.The average sediment yield rate increased by 1.31-3.51 and 7.70-8.58 times.As a whole,the influence of slope gradient on sediment yield rate was greater than that of runoff rate.2)The silt was the main particle composition of the eroded sediment on each slope,ranging from 47%to 55%depending on the flow discharge conditions.The Enrichment Ratio(ER)and Aggregation Ratio(AR)of eroded sediment particles with different grain sizes differed significantly.The ER of clay particles was less than 1,and the AR was more significant than 1,which indicated that the sediment particles of this size were quickly lost in the process of erosion and migrated in the form of aggregates.Furthermore,the ER of silt particles was more significant than 1,indicating that particles of this size were enriched in the eroded sediment.The AR of silt particles was close to 1,which stated that the majority of them migrated as primary particles.For different slopes,the enrichment ratios of clay and silt in eroded sediment increased with the increase in flow discharge conditions,indicating that the rise in discharge would affect the enrichment of fine particles.Under the conditions of high flow discharge,fine particles were more susceptible to enrichment.3)The volume fractal dimension varied from 2.43 to 2.63 in different flow discharge conditions and showed a decreasing trend with the duration of the scouring time.Furthermore,the volume fractal dimension had a very significant positive correlation with clay and silt content and a very significant negative correlation with sand content.The volume fractal dimension values were primarily determined by the clay particle content.The research can help to clarify the laws of the sediment particle size varying with the development of the rill erosion process on a slope.Meanwhile,it can provide data support and a theoretical basis for particle size selection of fingerprint factor and reveal the erosion mechanism on a slope.