大戸川における2，3の観測について

Abstract

This paper describes the some results of observation in Daido River which is nowcarring out in order to investigate the behavior of the natural stream channels, especiallythe flow structure, sediment transport and riverbed variation.The Daido River is a typical alluvial stream carring a large amount of sedimentload, since the main part of the geological structure in its mountainous catchmentconsists of much weathered granite. The area of its drainage basin is 189.7 km2 andthe mean gradient of the total plain course is about 4 x l0~. The maximum flow rate inflood seasons, according to recent records, is about 105m5/s and the amount of sedimenttransport is estimated at 105m3/year.The authors intended to measure the dimensions of bed scour by two types of simpledevices. The one was a 2.7 in-long iron rail with a movable ring of 15cm in diameterand the other a lm-deep pole of 10cm square tiles 5mm in thickness. Both devices wereset in six sections of the straight reach at intervals of 20 m and alternatively at eightpoints in a section to compare their efficiency of measurement. For the curved reach, the former type devices were set in five sections at intervals of 100m. Unfortunately, the results were not successful, and the defects of these devices were pointed out.The measurement of the bed load transportation is very diffcult in natural streams.In the Daido River, the most of the bed load carring into the main river Seta depositedat the confluence, and therefore the rate of bed load transportation could be obtained bymeasuring of the total volume of the deposited sediment. The observed values werecompared with the calculated ones by various formulas for bed load transportation.Furthermore, the water-stage hydrograph and the celerity of flood peak in some floodseasons were examined.