Satoshi NIWA, Taro UCHIDA, Hiroaki IZUMIYAMA, Wataru SAKURAI, Ryoichi OHNO, Hideki TERADA and Yoshifumi SATOFUKA
The purpose of this research is to improve the evaluation accuracy of sediment transport phenomenon in period after large]scale sediment production by one]dimensional riverbed variation calculation. We carried out a reproduction calculation of sediment transport phenomenon over the three years after large scale sediment production for Harukigawa of the Fujikawa river basin. Hirano's model which can express coarse grain formation of riverbed surface layer was applied to the study model, and, regime theory was applied for flow width evaluation. Furthermore, we considered increase or decrease of α value of the regime theory by due to the occurrence of double]row bar and influence of the stenosed terrain. By comparing calculated value and actual value estimated by differential analysis of elevation values at two time periods, according to the proposed method of setting the α value, it is found that accuracy to reproducibility improves with respect to the river bed variation height and the passing sediment volume. In addition, from the past research, three features of sediment dynamics after large]scale sediment production have been clarified. (1) A period in which sediment discharge is active continues for several years to several ten years after large]scale sediment production. (2) Deposit sediment at the time of large]scale sediment production remains in the basin even after the active sediment discharge period. (3) Deposited sediment coarsen with time, by the time the active sediment discharge is over, it is approaching the average particle size at time before large]scale sediment production. By the proposed method, the features of (1) and (2) were reproduced. Moreover, by this method, we could express the tendency of river bed to coarsen.
Key wordsFMountain rivers, Period after large]scale sediment production, Flow width, Regime theory