猪名川流域における開発とそれにともなう水文環境の変化

抄録

The Ina River Basin, situated in the northwestern suburbs of Osaka City, has been actively developed for residential area and golf links. The purpose of this paper is to clarify what effects development in this basin has on the water quality and the run-off of the Ina River.
By the way, in this paper an index of such development is calculated by the following equations which were proposed by Masami Ichikawa.Lm=Σaili/Σai (1)Lf=Lm/Lw (2)where Lm is the mean distance from the centers of the impervious areas to the stream guaging station, ai is the area of the i-th impervious land surface, li is the distance from the i-th impervious area to the guaging station. And Lf is the factor of the length of the impervious areas, Lw is the longest straight distance along the stream.
The writer calculates another index of development with the following equation. It is considered that the phenomenon that the longer the distance from the developed areas to the guaging station is, the less the effect of them appears in it.Ld=Σai/li (3) where Ld is the index of development, ai and li is similar to those of the (1) equation.
When the said equation is used, its object is only residential areas and golf links, which are under development every year and not the achieved ones. Its reason is that there is a tendency that the annual run-off ratio increases when development of the residential area and others is under development in the Ina River Basin, and it decreases after achievement of development.
The results of this research can be summerized as follows:
1) Run-off
a) When the writer correlated the annual run-off ratio with the two indexes of development in the Oi subdrainage basin which are multiplied by the standard deviation of the monthly precipitation every year, it became clear that the index, dealed with development of the golf links and the residential area. This shows that development of the golf links is the important factor which alters the annual run-off ratio. In the writer's opinion, the increase of the run-off ratio was caused by a decrease of the interception by lumbering the trees and that of the infiltration by the denudation of the surface soil, both of which were connected with development of the golf links. But with the completion of the golf links, the flatness of the hill and the partial recorvery of the vegitation by replanting the lawn will increase the temporary storage, and eventually decrease the run-off ratio.
b) Though the writer also tried to confirm the effect which development had on the annual run-off ratio in the Gunkobashi subdrainage basin with the similar method to that in the Oi subdrainage basin, he couldn't obtain the nice result. But it is thought that an increase of the annual run-off ratio for three years (1969-71) was doubtlessly caused by the residential area in this subdrainage basin which was remarkably developed at that time.
c) When the writer correlated the rising ratio of the hourly water-level, which was calculated by quantifying the variation of the water-level at Gunkobashi, with the indexes (Lf, Ld) of development, which was calculated every year, he could obtain the high coefficients of correlation, 0.9106 (Lf) and 0.8693 (Ld). This shows that the variation of the hourly water-level is closely connected with development.
d) The peak water-level before development appeared at first at Obe of the upper stream and next at Gunkobashi of the lower stream, but after development it appeared at first at Gunkobashi and next at Obe. It seems that this sight of the peak water-level was a result of development of the residential area, but the direct causuality is not clear.