During the period 1965 to 1968, determinations were made of salinity, temperature and velocity in the Kitakami River.
The salinity concentration of bottom layer is much higher than the surface layer at the lower end of the river. Consequently, the water of surface layer is fresh water and that of the bottom layer is salt water (Fig. 2).
The salt wedge type of the Kitakami River shows fine negligible mixing. This phenomenon is rare, because in the rivers empting into the Pacific Ocean, it is generally moderate mixing. The salt wedge type is caused by the level difference between the low water and the high water, but it is also caused by discharge, too (Fig. 3).
The salt wedge length affected by an influence of discharge. When discharge decreases into about 70m
3/sec, the salt water intrudes into upper stream, about 8 km point from river mouth. But, when discharge increases into about 400 m
3/sec, the salt water is restricted to the vicinity river mouth (Fig. 6).
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