Author(s): Fukuoka Shoji; Abe Tomonori
Linked Author(s): Shoji Fukuoka
Keywords: Gravel bed rivers; Braided channel; Field experiment; Grain size distribution; Large gravel; Dike breach; Inundation discharge hydrograph
Abstract: For flood control measures in a steep braided channel, it is important to understand the effect of bed material on the river-bed variation and to estimate inundation discharge hydrograph due to dike breach. In this study we carried out a field experimentation on riverbed variation and dike breach in the floodplain of the Joganji River, which is a very steep braided channel. We investigate the river-bed variation characteristics of low water channel in a steep braided channel and clarify the bed material grain-size group that controls stability of the riverbed. Furthermore, we affirm the role of gain-size distribution and large gravels on riverbed variation by comparing these results with those of field experiments on the Joganji River in 2004. The grain-size distribution of a gravel-bed river's low-water channels can be approximately estimate by measuring grain-size distribution at one location at a minimum and determining D60 for other locations. The authors have developed a computational method for predicting inundation discharge hydrographs with a high degree of accuracy using two-dimensional unsteady-flow analysis in which temporal changes in water surface profile (including at the dike-breach point) are given, but without taking into account temporal change in dike-breach cross-sectional shape, etc. This method was tested in field experimentation simulating a dike breach. The experimental results showed the method to be effective in predicting inundation discharge hydrograph due to dike breach. Furthermore, when used in combination with analysis of river inundation, the method can serve as the technological foundation for a system of predicting inundation with a high degree of accuracy.
Year: 2007