抄録
It goes without saying that present our country are ruined by soil erosion, landslips and river floods, etc., No problem is more urgent to conservate our lands. It is very important to study the landslips and river floods in the Japanese today.
The writer carried out the investigation of mechanism of landslips and their present situations and their influences to the river at the upper, drainage area of the Watarase River.
Conclusions of this paper are as follows:
Landslip. have taken place usually at the upper parts of the Watarase drainage area, and many of there are not found in Palaeozoic regions but in granite or agglomerate regions. But, palaeozoic and quartz prophirite rigions of the vicinity of Ashio town habe been waged by the damage from poisonous smoke of Ashio copper mine.
Types and scales of the landslips are different from rock's properties and scales of landslips in granite regions are the largest and those of palaeozoic regions of the most upper drainage area are very small.
The factors in these landslips are as follows:
Resistabilty to weathering from rocks and lower liquid limit of soils are original factors. On the other hand, the natural factors which are the structure of the geological profile, tie influence of rejuvenation, the degree of slope, the slope from. and the effect of vegetation cover are the natural occasional ones. And the human factors which are management of the forest and accelerate to natural erosion, Hence, these factors cause to landslips.
Great boulders from these landslips are accumulated on the river bed, so run off of the river increases quickly, and they cause to floods.
It is the basis of the flood control to checkk the landslips and wasted lands in the drainage area of the Watarase River.
