线格子法を用いた河床堆积物の粒径分析法の再检讨.pdf

人と自然 Humans and Nature, No.7,33-41, October 1996 原著論文 線 格 子 法 を 用 い た 河 床 堆 積 物 の 粒 径 分 析 法 の 再 検 討 加 藤 茂 弘1)・井 上 耕一一一一川TS2)・,自丿 津 弘3) Re-examination of the Analysis of Grain Size Distributions of the Coarse River-bed Material by the Line-Grid Method. Shigehiro Katoi-i1 1, Koichiro Inoue2) and Hiroshi Shimazu3 The line-grid method is a sampling technique which determines the size distribution of coarse river-bed sediments. We first estimated the range of the error of this method and determined the minimum number of sampling particles necessary to obtain objective accuracy . The error of the mean diameter(/3), with 80 percent reliability, is given by the following relationships | ft | 1.28n~1/2CvX , where n is the number of particles, Cv is the coefficient of variation, and X is the mean diameter. Based on our data, the value of Cv is estimated to be less than 1.3 with regard to the alternate bars in many Japanese rivers. Therefore, at least 300 particles are sufficient for most samples from coarse river-bed sediments, when the error( ft ) is within 10 percent of the mean diameter(X). Secondly, we propose the most suitable procedure in selecting a gravel sampling site to be as follows- 1) An alternate bar along the studied reach of a river is first classified into four areas (A, B, C, and D) by observing the sedimentary structure of its surface sediments; 2) Next, based on the micromorphological characteristics of the bar, it is classified into I , II , and III zones; 3) The combination of the two divisions thus leads to systematic classification of bars into 7 types or more. After this procedure, sampling lines are set up on the A area of the I zone or the B area of the II zon