Language：Japanese   Publisher：Japan Society of Civil Engineers  

The Kamanashi River is a steep river covered with gravel grains, cobbles and boulders. In 1982, the record breaking largest flood occurred and brought large scale sediment deposition in the river channels due to sediment yielding from the upstream mountainous areas. In addition, the grain size distributions became coarser in the upper reaches and finer in the lower reaches due to sorting during the flood. In this study, we developed and applied a flood flow and bed variation analysis method considering the nonequilibrium sediment motions of boulders, gravel grains and sands with large amount of suspended sediments in the 1982 flood. The developed model could explain that the bed materials in the downstream reaches became finer by fine sediment grains transported from the upstream to the downstream due to longitudinal sorting.

DOI： 10.11532/river.26.0_657

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

The Kurobe river has large amount of sediment supply , therefore it is difficult to maintain excavated cross sectional shape. For the purpose of maintaining excavated cross sectional shape, installing sediment flushing channel and training levee has been executed in Otozawa area, since 2017.


This paper indicated the effects of the sediment flushing channel and training levee on promotion of sediment flow based on the results of monitoring and simulations by using a depth-averaged flow and bed variation analysis of 2018’s flood. These results demonstrated that extending the training levee was more effective, and the improved design method was proposed.

DOI： 10.11532/river.26.0_633

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

The accurate flood forecasting technique is required to provide information of flood evacuations for residents in an inundation area. The run-off analysis in the flood forecast technique is usually verified by rating curves of rivers in general. But the rating curves can not accurately estimate discharge hydrograph in rivers where effects of flood storage and bed variations are large on flood flows. And the runoff from the small basins is not sufficiently verified. In the present study, the flood flow and bed variation analysis using observed water surface profiles provides accurate discharge hydrographs of the Hii River and the tributaries of 2013 flood. And parameters of the tank model are identified by using those discharge hydrographs. The flood forecasting technique using the verified tank model accurately predicts the time series of water surface profiles and discharge hydrographs of the 2011 floods in the downstream of the river.

DOI： 10.2208/jscejhe.75.2_i_1291

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Language：Japanese   Publisher：土木学会  

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© The Authors, published by EDP Sciences, 2018. In the sandy Hii River, a large amount of sediment yield from upper river basin had brought developments of braided channels covered with sand waves. In the braided channels, sediment materials on the river beds are capable to move in normal discharge conditions. In recent years, however, the sediment yield decreases due to constructions of check dams and ground sills in the upper river basin. Thus, the river beds downstream of the ground sill have gradually degraded and the main channel widths have been narrowed with the progressing bed degradation. Firstly, we clarified that the effects of non-equilibrium sediment transports around the ground sill during normal discharge conditions on the bed degradation and the channel width reduction by using annual observed data and numerical simulations for bed variations. In addition, we provided the river improvement techniques for mitigating bed degradation and channel width reduction by improving state of non-equilibrium sediment transports passing through the ground sill.

DOI： 10.1051/e3sconf/20184002033

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Language：Japanese   Publisher：土木学会  

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

It is important to establish a practical method for estimating sediment discharge hydrograph in rivers with a large amount of sediment yield during floods. In this study, we develop the practical method for estimating sediment discharge hydrograph by calculating flood flow and bed variation analysis in stages so as to bring the observed and calculated bed aggradation and channel migration closer to agreement. The present method was applied to 1995 flood of the Hime River. As a result, it shows that the present method could estimate sediment discharge hydrograph in rivers with a large amount of sediment yield during floods.

DOI： 10.11532/river.24.0_167

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Language：Japanese   Publisher：公益社団法人 土木学会  

 In the Hii River with braided channels, developments and deformations of sand waves during a flood affect flood flows and sediment transports. The Hii River floodway has a settling pond at the river bifurcation point for reducing sediment discharge to the downstream. For managements of the Hii River bifurcation section and the floodway, reduction of inflow sediment discharge into the floodway is required. The General Bottom Velocity Computation method was employed for computation of flood, which took account of time series of observed water surface profiles. We estimated flood discharges, bed variations and sediment transports in the river bifurcation section and the floodway during the flood of Sept. 2012. In addition, we propose reduction measures of inflow sediment discharge into the floodway.

DOI： 10.2208/jscejhe.73.I_895

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

In the sandy Hii River, sediment supplies from the upper basin have been decreasing due to constructions of check dams. The sediment transport in the Hii River occurs during not only the flood but also the ordinary discharge because of small and uniform sand composing the river bed. Therefore, river bed degradation and channel widths reduction downstream from the Igaya groundsill have developed due to non-equilibrium sediment transports at the groundsill during the ordinary discharges and small scale floods. We proposed proper shapes of the groundsill and river cross-section for mitigating the river bed degradations and channel widths reductions by using the numerical simulation model for long-term bed topographic changes in the river.

DOI： 10.11532/river.23.0_507

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

The Kurobe river forms alternate bars at downstream of the Aimoto weir. In this section, longitudinal dikes have been installed for bank protections of the flood channel. In 1995, a large flood occurred. Meandering pattern and flow attacking points of the main channel have been changed since 1995’s flood. Therefore, most of the longitudinal dikes have become not to work against bank erosions by flood flows. In this study, we considered that improvement of channels at downstream of the Aimoto weir was accomplished by recovering natural pattern of alternate bars. And, we carried out flood flow and river bed variation analysis in gravel-bed rivers in order to investigate the stability of the predetermined channels. As a result, it was confirmed that a proposed river improvement channel was useful and the existing longitudinal dikes were able to work against flood flows.

DOI： 10.11532/river.21.0_177

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Since the elevation of flood plains in the lower Ota River floodway is located in the intertidal zone, tidal flats formed on the flood plains have become important as one of river functions. However, the tidal flats are gradually reducing in size due to bed scouring year by year. So, the cross-sectional shape in the lower floodway has changed gradually and naturally to the ship-bottom shaped channels at present from compound channels in the beginning by flood flows. Therefore, it is necessary to design the riprap for protecting against the erosion of the tidal flats. In this study, we evaluate effects of ripraps on the topographic changes and provide appropriately ripraps design by using numerical simulation for flood flows and bed variations in the lower Ota River floodway. Finally, issues to be considered in the design of a ship-bottom shaped channel which are found in the present study are summarized.

DOI： 10.2208/jscejhe.70.I_1093

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：INT ASSOC HYDROLOGICAL SCIENCES  

A channel network consisting of the Ota River floodway and five branched rivers is formed on the Ota River delta. To estimate bed variation and flood discharge distributions in the channel network of the Ota River delta is important for proper river management. The objective of this study is to develop the calculation method of flood flows and bed variations by using time series of water surface profiles measured in the-channel network of the Ota River delta. We developed a quasi-3D numerical model for the flood flow and bed variation analyses using time series of observed water surface profiles. The unsteady quasi-3D analysis of flood flows and 2D analysis of bed variations using time series of observed water surface profiles are found to provide good explanations for the flood discharge distributions and bed variations of the channel network on the Ota River delta.

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Language：Japanese   Publisher：公益社団法人 土木学会  

A network of channels which consists of the Ota River floodway and five branched rivers is formed in the Ota river delta. To estimate flood discharge hydrographs and bed variations in each channel is important for proper river management. Therefore, we developed a numerical model for the flood flow and bed variation analysis using time series of observed water surface profiles with the networked rivers in the Ota river delta. As a result, the unsteady quasi-three dimensional analysis of flood flows and two dimensional analysis of bed variations using time series of observed water surface profiles is found to provide good results for the flood discharge distributions in the networked rivers in the Ota river delta.

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Language：Japanese   Publisher：公益社団法人 土木学会  

  In the Ota River, we had investigated kind, positions and properties of vegetations and prepared to measure temporal changes in water surface profiles of a flood. In 2005, the largest flood in the past 50 years occurred in the river. Vegetations on sandbar formed inner bank side were destructed by the flood flow. Unsteady 2D analysis of flood flow and bed variation using observed temporal changes in water surface profiles demonstrate the flood flow characteristics, bed variations and mechanism of vegetation destruction. Vegetation destruction was caused by the bed scouring of sandbar. The concept and means for the vegetation management are derived from the present investigation.

DOI： 10.2208/jscejb.66.47

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