著者

吉良 八郎 石田 陽博 畑 武志

出版者

神戸大学

雑誌

神戸大学農学部研究報告 (ISSN:04522370)

巻号頁・発行日

vol.11, no.2, pp.301-318, 1975

被引用文献数

3

---

In Japan, about two thirds of its land are the mountain districts, and its topographic and geological features are inevitable to erosion and collapse. The land is a zone frequented by typhoons with erosive dangerous rainfall. Thus the erosion rate is more than four times of the world average, and the production of sediment and its runoff are very important problems. When a group of dams for flood control and water utilization is constructed across sand-drifting river for the development of a river basin, the phase of the river channel will change so as to be in a new state of equilibrium. At the upper stream of dam sites sedimantation occurs due to the change in the state of river flow. The sedimention has some advantages, but it is essentially a loss to the flood control and water utilization owing to the reduction of storage capacity. It also causes rapid increase of interior flooding by the aggradation of river bed and the rise of groundwater level. On the other hand, at the downstream of dam sites degradation of river bed occurs due to the scouring or sorting caused by the variation of river flow, or by the kinetic energy of flow. In this way river bed approaches the final equilibrium gradient, and its final profile has a static equilibrium bed slope on which the tractive force is identical with the critical tractive force. Studies on the mechanism of sedimentation, such as the rate of sediment inflow and sediment distribution, are necessary to solve the sediment problem in order to establish a sedimentation policy. Observations on the state of sedimentation are a prerequisite. Observation data of sedimentation at 354 dam sites including electric-power dams, irrigation dams, water supply dams, flood control dams and multiple purposes dams are collected here in 1971,and the respective features are analyzed. Data are obtained as the sediment accumulation at many dams in the country. Thus the sediment indices in Japan, such as original storage capacity C(m^3), amount of total sediment Q_s(m^3), total rate of sediment accumulation R_s=100(Q_s/C) in percent, mean annual sediment accumulation r_s=R_s/Y in percent, specific sediment accumulation q_s=Q_s/FY(m^3/(km)^2,year), and time in years since the completion of the dam Y in years, are survayed macroscopically and quantitatively. And the features of respective reservoir are investigated. By studying in detail the sediment indices on the basis of the sediment accumulations at dams, the variation of characteristics can be estimated for respective regions, river systems or years.