On the Inundation Disasters by the Heavy Rainfall on August 4th through 7th, 1979, in the Kitakami Drainage Basin, Iwate Prefecture
1980 Volume 32 Issue 3 Pages 127-137
Details
1980 Volume 32 Issue 3 Pages 127-137
From the 4th to the 7th of August, 1979, the active “Bai-u” front passing through Iwate Prefecture in Northeast Japan brought about a heavy intermittent rainfall and it caused inundation disasters along the main stream of the Kitakami River. The damage by the inundation amounted to over 11 billion yen the whole prefecture.
The inundation brought about two types of damage along the main stream of the Kitakami. One of these is directly due to the rising of the Kitakami, which caused a flood over a wide area, stagnant for a long time. This type of damage typically occurred at the lower reaches of the Kitakami Basin, especially in the Ichinoseki area.
The other type is inundation disasters on account of the countercurrents of tributaries and the unworkable draining of channels. Such damage is rather artificial in that the residential sections have been constructed in marshy areas of flood plains, back swamps and abandoned channels. This type of damage typically occurred in the Hanamaki area.
Considering these damages by inundation disasters, the writers will point out some important problems as given below concerning the development of the Kitakami River.
1. The dams constucted at the tributaries drain off to control the water level of their dam-reservoir during a heavy rainfall. This raises the water level of the main stream of the Kitakami. The heavier it rains in the drainage of tributaries, the more damage is caused by inundation disasters along the main stream. In Constructing dams, we need to consider the balance of the water level of all the drainage basins.
2. We can appreciate the value of the “Yusui-chi” project in the Ichinoseki area (“Yusui-chi” means a land for pooling flood water). It should be kept in mind secondary inundation disasters such as the countercurrents of tributaries of the flood through the unworkable draining of channels may be caused by the construction of artificial embankments.
3. The more urbanization progresses and the more residential sections are formed in marshy areas, the greater damage of inundation disasters will occure. It is therefore necessary that the local public bodies consider how to keep off such disasters.
