Abstract
Field measurements have been carried out at the mouth of the Nanakita River, the catchment area being 229km2, with the object of finding difference of topography change between small and large rivers. The cross-sectional area at the mouth attained to its equilibrium state very rapidly as compared with large rivers. Another distinct difference can be seen in the water level rise, or wave set-up, measured in the mouth. Furthermore, time-variation of the water level inside the river showed remarkable reduction of the amplitude and also phase shift behind the tidal variation in the ocean. On assuming a triangular or parabolic section, the width and the maximum depth at the gorge section are determined to minimize the difference between computed and measured water level inside the river.
