坡面侵蚀过程中泥沙分选特征及其搬运机理

Soil erosion by water involves the processes of detachment, transport and deposition of soil materials by the erosive forces of raindrops and runoff. There is a need to describe sediment sorting to characterize the on-site and off-site effects of soil erosion. A better understanding of sediment sorting will improve understanding of erosion and sedimentation processes, which in turn will improve erosion modeling. More information on sediment sorting and its dynamics is needed to better understand the behavior and interaction of the different components that make up erosion processes.To address these issues, typical soils from the Loess Plateau were chosen in this project. This project thus will compare the dynamics of soil erosion processes and particle-size selectivity at laboratory and field scales. The methodological approach used here makes use of simulated rainfall for both field- and laboratory-scale experiments. The time variation in size distribution of the exiting sediment resulting from erosion under simulated rainfall was measured in detail using a laser diffraction device, and these data were used to interpret likely transport mechanisms. .Specific objectives of this project were: (i) to determine the quantity and the size characteristics of the eroded sediment at both field and laboratory scales; (ii) to evaluate the erosion processes affecting sediment transport and size-selectivity of this sediment; (iii) to identify different mechanisms affecting particle transport by raindrop and flow; (ⅳ) and to provide a data set useful to the understanding (and potentially the modelling) of fundamental erosion processes, their interactions and their spatial and temporal variability. This research will improve our knowledge of soil erosion processes operating on hillslopes and provide insight into improving the design, maintenance, and usage of slopelands.

坡面侵蚀过程中，泥沙运动形式和输移距离不仅取决于坡面径流水动力学特性，还与泥沙颗粒大小、密度等自身的性质有关。侵蚀泥沙颗粒分布受土壤侵蚀过程及侵蚀方式演变和土壤性质影响。迄今为止，坡面侵蚀过程中泥沙颗粒分布规律仍没有定论,不同粒级的泥沙颗粒搬运机理有待深入。本项目选择黄土高原黄绵土、黑垆土与沙黄土为主要研究对象，以传统的坡面侵蚀过程监测与新兴三维激光扫描技术、激光粒度分析方法相结合，研究坡度、坡长、土壤、降雨、径流等因素对泥沙输移过程及其颗粒组成变化规律的影响，阐明坡面薄层水流和细沟水流中泥沙颗粒的迁移和转化特点；基于对不同粒级泥沙颗粒搬运方式和机理的认知，建立薄层水流和细沟水流的泥沙搬运能力定量表述。研究成果对深化坡面土壤侵蚀内在规律的研究有一定理论意义，为建立具有物理成因的侵蚀模型奠定理论基础。

坡面侵蚀过程中，泥沙输移不仅取决于降雨和径流的侵蚀动力，还与泥沙颗粒大小、密度等自身性质有关。揭示泥沙分选规律及其搬运方式对深入认识侵蚀机理有重要科学意义。由于研究缺乏系统性，陡坡侵蚀过程中泥沙分选规律仍未定论，搬运机制有待深入探讨。本项目选择黄土高原典型土壤为研究对象，以侵蚀泥沙的颗粒分布和变化规律为线索，在较大坡度范围（10-25°），利用激光粒度法研究了坡面侵蚀过程中泥沙粒径分布与变化规律。泥沙颗粒呈双峰分布，<0.15 mm小粒径和>0.50 mm大粒径的泥沙比0.15-0.50 mm泥沙更易被搬运。综合泥沙运动力学原理和薄层水流水动力学特征，发现陡坡条件下大粒径泥沙以滚动方式搬运，小粒径侵蚀泥沙则以悬浮/跳跃方式快速搬运，但这两种搬运机制对中间粒径输移效率均较低。结果阐明了悬移/跃移和滚动搬运机制分别输移不同粒级的泥沙颗粒，确定了坡面细沟间和细沟侵蚀形态下滚动搬运的贡献率在10-25%间，建立了水流功率与滚动搬运贡献率的模型。揭示了缓坡研究结果不适用于陡坡侵蚀环境的根源：只考虑了泥沙的悬移/跃移搬运机制。相关成果发表在Journal of Hydrology、Soil Science Society of America Journal、Geomorphology等本专业重要SCI期刊，共计10篇，其中70%以上属于JCR分区1区，至2017年1月10篇论文SCI他引81次，培养博士2人。