我国砒砂岩区属于多营力复合侵蚀区,其中水力侵蚀是各侵蚀物质输移的主要载体。选取位于裸露砒砂岩剧烈侵蚀区的二老虎沟小流域为研究区探讨砒砂岩区小流域场次洪水产流产沙特征,细化区域水蚀过程。2018年8月采集了小流域两层泥沙沉积旋回样及对应的侵蚀物质来源,结合泥沙沉积旋回样对应的降水、径流、泥沙数据进行了分析。以洪峰所在时间将两次洪水事件命名为20180716(1号)和20180719(2号)。结果 表明:流域雨前土壤含水量及雨型差异是决定流域产流开始时间和初损量的主因。1号洪水径流量、输沙量分别为2号洪水对应的该值的2.7倍及3.4倍。粉粒、中砂粒、细砂粒为二老虎沟小流域坝地沉积旋回样的主要粒径,占比达70%。两场次洪条件下小流域泥沙淤积状况存在差异,与1号洪水的沉积旋回样相比,2号洪水的沉积旋回样粒径粗化。黏粒、粉粒、极细砂粒占比减少,细砂粒、中砂粒、粗砂粒的含量增加。利用Weibull分布拟合了二老虎坝地泥沙沉积旋回主要物质来源(地表覆土及裸露砒砂岩)的理论分布曲线,在此基础上根据最小二乘准采用差分进化算法求得沉积旋回层的物质来源比例,结果显示砒砂岩为两场洪水沉积旋回样中的主要侵蚀运移物质。
The Pisha Sandstone area in China is an erosion zone affected by multiple forces, with water erosion being the main erosion force as well as the transport carrier of erosion materials. In order to better understand the processes pertaining to regional water erosion in a region of intense erosion made of Pisha sandstone and frequently affected by floods, an analysis of the characteristics of the runoff and sediment yield in the Erlaohugou watershed was conducted during flood events in this study. In August 2018, we carried out sampling of erosion materials and two sedimentary cycles in the region. The precipitation, runoff and sediment data corresponding to sedimentary cycles were analyzed. Hereafter, the flood which the flood peak the 20180716 was chosen as the reference as NO.1, and the flood which the flood peak 20180719 was chosen as NO.2. The initial soil water content and the pattern of rainfalls are the two main factors that determine the starting time and the initial loss of the runoff. The runoff and sediment transport of NO.1 are 2.7 times and 3.4 times of the value corresponding to NO.2, respectively. The types of dominant sediment in the sedimentary cycles are medium sand, fine sand and silt, accounting for 70%. The siltation in the basin changed depending on changes of the flood conditions. Compared with the sedimentary cycle of NO.1, the particle size of the sedimentary cycle of flood NO.2 is coarsened. The proportion of clay, silt and extremely fine sand decreased, while the content of fine sand, medium sand and coarse sand increased. This study also considered the use of the Weibull distribution to establish theoretical distribution curve of the particle size distribution of the erosion materials(surface soil and bare Pisha Sandstone)in the Erlaohugou watershed. On the basis of this, the proportion of erosion materials in the sedimentary cycles is obtained by differential evolution according to the least square criterion, and it is found that Pisha Sandstones are the main erosion materials in the sedimentary cycles.
