尼龙网方格沙障风沙流携沙粒度的空间分异特征

Spatial Distribution of Grain Size in Aeolian Flow in Nylon Net Checkerboard Barrier

为了探究塔克拉玛干沙漠腹地尼龙网方格沙障对风沙流携沙粒度的空间分异作用,于2015年4—6月,选取裸沙地和尼龙网2种下垫面,利用方口集沙仪和全方位集沙仪分别收集风沙流中垂直高度层中2~100cm和16个方位的输沙量,利用BT-2001激光粒度分布仪对沙样进行粒度组成分析。结果表明:沙粒的粒度频率曲线形态表现为单峰分布特征,与下垫面沙粒组成有关。在垂直方向上,沙粒的平均粒径在L1(裸沙地)、L2(沙障前部)处随着高度的增加沙粒平均粒径减小,L3(沙障中部)处平均粒径先增加后趋于稳定;风沙流进入沙障后,分选性变差,偏度增大,峰度减小;L1和L2处沙粒随平均粒径的减小,分选性变差、细尾越来越明显、沙粒粒径分布范围变窄,且L1处分选系数、峰度和偏度与沙粒平均粒径在双变量图上的变化率大于L2处。在水平方位上,沙粒的平均粒径在T1(裸沙地)-T2(沙障前部)-T3(沙障中部)的过程中先增后减,在T2处,分选性最好,偏度系数和峰度最小;3个观测点的粒度参数与平均粒径没有明显的相关关系。

The research on grain size is of great importance in aeolian geomorphology. On one hand, grain size characteristics of the surface sediments not only reflects the wind for transporting and sorting but also records the wind strength formation of the aeolian process. On the other hand, it embodies that terrain and other obstacles have made a big change on the sand flow transport processes. Thus, studying the spatial dis- tribution of grain size in aeolian flow in the hinter land of Taklimakan Desert is extremely important. To re- veal spatial distribution of grain size in aeolian flow, two kinds underlying surface, bare sandy land and ny- lon net checkerboard barrier, were selected in this study. Using two kinds of sand collectors （one was set to observe sand flow in the vertical height, the other was set to observe sand flow in the horizontal direction） to measure sediment runoff of sand flow in 2-100 cm and 16 directions. And then the grain size of sand samples was analyzed by BT-2001 Laser grain size analyzer. The results show that the shape of frequency distribution curves of grain size is unimodal. In the vertical height, the average grain size of sand grains at the L1 and L2 decreases with the increase of height. At L3 average grain size increase before it is stable. With the degree of depth in the sand barrier, sorting is worse; skewness increase, kurtosis reduces. With the decreasing of mean grain size, sorting is deteriorating. The thin tail of frequency distribution curves be- comes more and more obvious. Grain size distribution is narrowed at the L1 and L2. At L1 the change rate of mean grain-size to standard deviation, skewness, kurtosis is greater than at L2. In the horizontal direction, the average grain size of sand have the first increase after a decrease during T1--T2--T3. At T2, sorting is the best, skewness and kurtosis are minimum. Size parameters and the average particle diameter have no significant correlation in the three points.