Abstract
To make clear the character of the flood by the Kanogawa Typhoon, the writer studied the transformation of the river beds and the flood in the lower stream area of Kano gawa.
The results of the survey are summarized as follows:
1. Kano gawa runs northward in its middle and lower stream, deepening in alluvial plains.
2. In comparison with the cross sections of the river beds three times during measured 1941 to 1958, a lowering of the river bed is found in many parts.
3. Meanwhile, according the cross sections before and after the Kanogawa Typhoon at each point of 200m interval along the river, the quantity of the accumulated silt, sand and gravels in the river bed in the lower stream area below Ohhito (26km S. from the mouth of the river) is calculated as the amount of 5_??_6×105m3. The great part of the these matters accumulated in the limited part, and its quantity corresponds comparatively well to that of the silt, sand and gravels brought out from the up-side of depositional one.
4. The erosion of the river bed is particularly marked in the part where gradient changes suddenly and in the up-side of the broken bank. Namely the erosion took place even in the area of the lower stream. Accordingly it is not right that the area of the lower stream of the Kano gawa is a depositional one.
5. The movement of the river bed gravels are not altogether remarkable even in such a great flood by the Kanogawa Typhoon.
6. Though the quantity of silt accumulated by the flood in thd protected lowland cannot be calculated exactly, it is estimated to be between 2_??_10×105m3. It is understood that this quantity includes mud from the broken banks (3×105m3), silt of the river beds away at the breaking of embankments and silt produced by erosion in the protected lowland.
7. It is impossible to consider that, during the great flood of the Kanogawa, all of the debris from mountainous areas of the drainage of the Kanogawa have been transported and accumulated directly into the lower drainage area.
