淤地坝坝系泥沙粒径组成与变化特征研究

Study on the Composition and Changeable Characteristic of Sediment Particle Size in Check Dam System

了解小流域淤地坝坝系泥沙粒径组成与变化特征是认识和评价淤地坝拦减粗泥沙作用的基础和前提.本文通过对黄土丘陵区王茂沟小流域不同泥沙源地和淤地坝坝系沉积泥沙的取样与分析,研究了坝地泥沙粒径组成的变化过程与特征.结果表明：淤地坝泥沙沉积过程中,黏粒含量均小于10%,沙粒含量在30%-40%,沉积泥沙的粒径组成大都以粉粒为主.除草地外,流域内不同侵蚀源地泥沙粒径组成的差异不大.尽管流域内各座淤地坝之间泥沙粒径组成有一定程度的变化,但最上游与沟口坝地的粒径组成没有明显差异,流程远近与各级粒径含量变化不相关.王茂沟流域现有淤地坝坝系是粗细均拦,淤粗排细作用不明显.

Understanding the composition and changeable characteristics of sediment particle size in check dam system is the foundation and prerequisite for studies on the role of check dams in retaining and reducing coarse sediment（ 0. 05 mm） in a small watershed. Based on the analysis on the particle size from different sediment sources and check dams in the Wangmaogou watershed in the Loess Hilly Area,the changeable process and characteristics of sediment particles in the check dam system were studied. The results showed that the silt particle（ 0. 002 -0. 05 mm） accounted for more than 50% of the sediment in the check dams,the content of clay particle（ 0. 002 mm） and coarse particle（ 0. 05 mm） took about less than 10% and30% - 40% of the total,respectively. In the watershed the difference of soil particles among various sediment sources is not large except for the grassland,and the difference between dam lands and the sloping farmland is very small. Though the composition of soil particle among check dams is different,it has nearly no any difference between the first dam in the upstream and the last one in the downstream in the watershed,and the flow distance is not related to the change of particle size at all levels. So,the existing check dam system has retained both the fine（ silt and clay particles） and coarse particles sediments,and the role of check dams in retaining the coarse sediment and discharging the fine is not obvious in the Wangmaogou watershed.