Sabo-logical studies on the self-adjustment of the river channel

To carry out Sabo works effectively，the felation among the grequency，the channel characteristics and the history of sediment movement must be understood clearly.In this study，the process of sediment movement of the Oi river in central Japan and of the Saru River in Hokkaido has been investigated.The main results are summarized as follows：1.As we made an analysis of sediment yield from the viewpoint of the basin scale(Large Space Scale)。The volume of specific sediment yield of the oi river basin was2000to6000(m^3/Km^2/year)，which was10to30times the volume of specific sediment yield of the Saru river basin.2。The basic caracteristics of sdiment movement both the OI river and the Saru river are similar.In case of Higashigochi experimental torrent，the sediments which exceeded 150，000立方公尺in volume deposited on the riverbed of the observation reach by the flood due to typhoon no，10，on august1-3，1982。Since then，rapid erosion of the riverbed ensued and the riverbed has been recovering its former profile，and also the channnel has been nearly regaining its former shape and from。And also it seems that thus changes happen in the Saru river.3。As described above，it seems that a natural torrential river adjusts its channel slope and channel geometry to approach a dynamic equilibrium condition for given external constraints，such as water and sediment discharge，valley slope and width，geological constraints and others.4。In the scouring process after large deposition，changes of the volume of riverbed variation per unit peak discharge can be expressed by the@equation of S(T)=-exp(-t)，where S is the volume of riverbed variation per unit peak discharge，t is the order of flood occurrence which is expressed as1，2，…，or is the constant。

To carry out Sabo works effectively, the felation among the grequency, the channel characteristics and the history of sediment movement must be understood clearly. In this study, the process of sediment movement of the Oi river in central Japan and of the Saru River in Hokkaido has been investigated.The main results are summarized as follows: 1. As we made an analysis of sediment yield from the viewpoint of the basin scale(large space scale). The volume of specific sediment yield of the oi river basin was 2000 to 6000 (m^3/Km^2/year), which was 10 to 30 times the volume of specific sediment yield of the Saru river basin.2. The basic caracteristics of sdiment movement both the OI river and the Saru river are similar. In case of Higashigochi experimental torrent, the sediments which exceeded 150,000m^3in volume deposited on the riverbed of the observation reach by the flood due to typhoon no, 10, on august 1-3,1982. Since then, rapid erosion of the riverbed ensued and the riverbed has been recovering its former profile, and also the channnel has been nearly regaining its former shape and from. And also it seems that thus changes happen in the Saru river.3. As described above, it seems that a natural torrential river adjusts its channel slope and channel geometry to approach a dynamic equilibrium condition for given external constraints, such as water and sediment discharge, valley slope and width, geological constraints and others.4. In the scouring process after large deposition, changes of the volume of riverbed variation per unit peak discharge can be expressed by the equation of S(t)=- exp(- t), where S is the volume of riverbed variation per unit peak discharge, t is the order of flood occurrence which is expressed as 1,2,・・・・, or is the constant.