大戸川に関する調査研究

Abstract

This paper describes the some considerations on the behavior of the sediment in theRiver Daido which is a typical alluvial stream carrying a large amount of sediment load, since the main part of the geological structure in its mountainous catchment consists ofmuch weathered granite. The area of its drainage basin is 189. 7 km2. The recentrecorded flood occurred in 1953, when a large amount of sediment about 4 x 106 m8 wasyielded and the greater part of the sediment deposited in the flood plain, while the ave-rage of sediment yield is estimated at 10~ m2/year. The characteristics of the disasterdue to the sediment was discussed with relation to the geographical features. Sedimenttransportation in the River Daido was calculated by using Brown formula from 1924 to1959. The result showed fairly good agreement with the observed volume of the depo-sited sediment in the Omine reservoir downstream. Grain-size distribution of the sedimentwas examined of the various places of the hill-side and of the river bed.The distribution of the concentration and grain-size of the suspended sediment andthe structure of the turbulence were observed in 1969 flood. From these observations itwas revealed that the fall velocity of the max. grain-size of the suspended sediment isapproximately equal to the shear velocity, and the average grain-size distribution is nearlyequal to the distribution of the part smaller than max. grain-size of the suspended mate-rial in the yielded sediment at the hill-side.