矩值法和图解法计算山区河流沉积物粒度参数的差异

在宜昌市山区小河莲沱溪采集一组以粗砂和极粗砂为优势粒度组成的沉积物样品,在筛析法进行粒度分析的基础上,用矩值法和图解法分别计算沉积物的粒度参数,并对两种方法所得的结果进行对比.两种计算方法得到的平均粒径和分选系数十分接近,基本上可以互相替代.峰态呈一定的相关性,但不可互相代替.偏态较为离散,不具有明显的相关性.分析发现...

The Difference between Moment Method and Graphic Method for Calculating Grain-size Parameters of Sediments in Mountain Streams

Taking a set of sediment samples which consist of coarse sand and very coarse sand with preponderant grain-size from a mountain stream named Liantuo in Yichang area,then on the basis of grain size analysis with the sieve analysis method,to calculate the grain-size parameters of sediments with the moment method and graphic method separately;the results of the two different methods are compared.The average grain diameters and sorting coefficients of the two methods are very close;they could almost replace each other.The kurtoses of the two sets of data have a correlation but they couldn’t replace each other;but the skewness of them is dispersed;they didn’t have an obvious correlation with each other.Analysis proved that the reason which created the difference has a relationship with the counting principle of the two different methods and the grain composition of the coarse grained sediments.The coarse grain skewness calculated by the two methods don’t have an obvious correlation with each other;the skewness values derived from the graphic method has indicated the tail of grain-size;while the skewness value derived from the moment method has reflected the whole characteristics of grain-size.For the kurtosis values derived from the two methods,when the fraction distribution curve of the sample is unimodal and centralized,the difference between the results derived from the two methods are insignificant;while when the fraction distribution curve of the sample is double-apices and the times peak frequency value is comparatively high;the results derived from the two methods are quite different.The calculation of the graphic method doesn’t take the grain-size characteristics of the tails of both ends into consideration;it may lead to calculating error of the grain-size parameters,however,the moment method is more scientific and the calculating results are more exact.So in the process of integrating and assimilating the information,the difference lies in the calculation of the grain-size parameters derived from the two methods should be taken into account.