沖積河川における河床砂れきの特性の変化について

Abstract

The authors investigated characteristics of the bed materials of the Hira River flowinginto the west side of Lake Biwa of which the basin area is 11.58km2. It was found that thedistributions of size frequency of the bed materials were classified three patterns, such asskew distributions in an upstream reach of the river, distributions with binoininal peaksin a middle reach and log-normal distributions in a downstream reach. Changes of thesedistributions of size frequency of the bed materials with distance can be explained bythe sorting effect of running water.An equation for calculating the distribution of size frequency of the bed materials isproposed on the basis of the assumption that the sand and grayel of maximum size in thebed materials are in the critical condition for movement. Calculated values of the maximumand median sizes, standard deviation and skewness of the bed materials are in good agree-ment with observed ones.