Abstract
The writer conducted an investigation of the relationship between the rainfall accompanying the Kanogawa typhoon and its resultant landslides, including landslides and the transportation of materials produced by landslides, and the scouring and deposition produced by the flood of Sept. 26, 1958 in the upper drainage basin of the Kano River (Fig. 1).
Many investigations have been made of the various forms of damage caused by heavy rainfall, such as landslides, scouring, transportation and deposition produced by flood water, but little work has been done on the relationships between these phenomona from the upper to the lower course in a drainage basin.
The main purpose of this paper, therefore, is to make clear these relationships.
The conclusions of this paper are summarized as follows:
1) In the upper drainage basin of the Kano, many landslides have occurred as a result of heavy rainfall accompanying typhoon No. 5822. The severity of these landslides is especially high in an area from the southwestern to the northeastern part of the town of Yugashima (Fig. 2). These landslides have also coincided strongly with the area of heaviest rainfall even occurring in the area of the same rock type. From these observations, it might be said that there is little relationship between the distri-bution of landslides and of rock types, but that there is positive relationship between the distribution of landslides and of rainfall amount. The area where landslides are most frequent coincides with that the amout of rainfall is from 550 to 700mm. during this period of the typhoon (Fig. 2, Kawamura's Figs. 3 and 4).
2) Many boulder-size terrace gravels were also removed from riversides to stream beds by the scouring of flood water in the upper course from Yokose which is a town of Shuzenji (Fig. 1). Materials produced by landslides are mostly deposited on the mountain-sides and in small mountain stream beds except for landslides extending to the river beds.
3) It has been found by many researchers that the materials produced by landslides were transported only a very short distance, while the writer found that the bulk of the materials—derived from the great landslide in Ikadaba which is situated in the upper reach of the Omi River (Fig. 4, Tab. 3 and Photo 1) and composed of pumiceous sand and gravel was transported very long distance by the water of only one flood.
4) The locality of scouring and deposition by flood water could be determined by geomorphological characteristics such as the relationship between the ratio of river-width to valley-width and the stream gradient (Fig. 6, abscisa: the ratio of river-width to valley-width, ordinate: stream gradient). Geomor-phological factors determining the locality of scouring and deposition by flood water seem to be very important for flood control.
