Abstract
This paper analyses the composition of channel network, especially parameters of Horton's laws, and discusses the characteristics of drainage basins in Japan. Basic data are collected from 180 partial drainage basins in the whole country and 19 full drainage basins in Hokkaido.
Horton's laws of drainage net composition hold well in drainage basins of Japan as well as in drainage basins of other countries. Parameters of Horton's laws vary slightly from area to area and from geology to geology. Ranges of values of the bifurcation ratio, the drainage area ratio, and the stream fall ratio are about the same between the partial drainage basins and full drainage basins. There are some differences in the ranges of values of the stream length ratio and the stream slope ratio between the partial drainage basins and the full drainage basins. These values of the full drainage basins are greater than those of the partial drainage basins. It is considered that these differences are due to more frequent meandering of rivers in middle and lower parts of drainage system. The linear relation is found between the bifurcation ratio and the drainage area ratio, and the slope of its regerssion equation is nearly 1.0. It is interesting that the drainage area ratio is always about 0.4 greater than the bifurcation ratio.
The average of the bifurcation ratio of drainage basins in Japan is 4.24, which is greater than a theoretical value of 4.0. The average of the stream fall ratio is about 1.0 for drainage basins in Japan. Drainage basins are considered, in general, to be in the stage of maturity in stream channel development in Japan. As the stream channel is liable to develop on an originally inclined land surface, the frequency of excess stream is greater in Japan than in other continental countries. Although the stream bed is nearly in dynamic equilibrium, it tends to be slightly aggraded, especially in fresh volcanic rocks areas.
