TOGO Masami Professor, Hosei University, 社会学部, 教授 (70061231)
INOUE Tomoo Assistant, Professor Hosei University, 第二教養部, 助教授 (50193595)
SATOH Norihito Professor, Hosei University, 文学部, 教授 (90097147)
|Budget Amount *help
¥2,400,000 (Direct Cost: ¥2,400,000)
Fiscal Year 1988: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1987: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1986: ¥1,300,000 (Direct Cost: ¥1,300,000)
This paper deales with the variation of river-bed in the outer zone in south-west Japan--especially the characteristics of the river Shimanto in Shikoku--. The resull of the survey are summarized as follows.
1) It shows area of the most abundant rainfall and high frequency of floods in Japan. So,design flood of R.Shimanto has been determined 14,000m<@D13@>D2/s since 1890 and its quantity belongs to no.three in Japan now.
2) According to the geological structure and crustal movement,the longitudinal profile of R.Shimanto has been slowly graded, meander has increased and hed-rock has appeard in middle and upper course.
3) In spite of the heavy rainy region mentioned above the sediment yield is a very low in flood and it may be transported by solution and suspension. As a result of our observation, We can safely say that it may be transported 2-3x10^5m^3/year.
4) Judging from the accumulation layer of the alluvial plain in the lower course of R.Shimanto, the speed of the deposition is about 0
.002m per year.
5) The variation of the river-bed of the Shimanto between 1968 and 1985 shows -0.035m in hight. But in this period, as we can see,drastic sand and gravel mining in most rivers of Japan,if we calculated except like this sand and gravels it shows -0.016m per year and by measurment after 1975, prohibited sand and gravel mining, it shows -0.003m per year. So,we could classify the Shimanto river as belonging to the degradutional type.
6) As a result of obserbvation of other river-beds in the outer zone, we can recognised that R.Mononobe shows 0.039 m 0.01m/year, the Niyodo river shows 0.027 0.01m/year, the kino river shows -0.016m 0.01m/year and the Ohyodo shows 0.008m 0.001m/year. So, according to the Variation of the river-beds of allmost all rivers in the outer zone, we can classified 2 types, i,e, the unchanging and degradational type.
7) Recently, according to the remarkable degradation of the river-bed of the Shimanto,salt intrusion length from the sea become longer than before, distribution of sea-fish changed, and the danger of new flood types appeard.
8) Further examination is required to determine contineously the depth and the solution and suspension of deposited materials in bottom of the Tosa bay.
This can be accomplish more frequent and thorough surveys and thoroug use of methods. Less