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結氷河川の解氷現象は，水位の急激な上昇を引き起こすアイスジャムの発生の可能性がある．河川結氷時の河道内工事や流量観測を実施する際には，作業計画および安全面から，解氷現象に関する知見および河道内の氷板厚を計算する技術が求められている．結氷河川における解氷現象を解明するために，氷板厚を連続的に測定し，熱フラックスを用いた氷板厚計算モデルを用いて，放射・対流，積雪，流水の3因子が氷板厚の変動に与える影響を評価した．本計算モデルを基にして，積雪と晶氷の影響を係数α，河氷の融解の影響を係数βに織り込み，気温，水温，有効水深から氷板厚を計算する実用的な計算式を開発した．さらに，気温から水温を計算し，有効水深を一定値とすることで，気温データのみから氷板厚を計算可能であることを示した．

Formation of bars indicates meandering of flow and deposition or erosion in river bed. It is necessary for river improvement and water utilization to clarify this phenomenon.Therefore many researches have been conducted on bar formation. In our previous study, it was found that the channel formation process was influenced by the form of hydrograph and duration of discharge recession period. The purpose of this study is to determine the influence given to channel formation by difference of discharge recession pattern in detail. Experiment conditions are case of constancy and variation in discharge recession speed.It is found that the channel formation process is strongly influenced by gradient of hydrograph at discharge recession period. That is, the relationship both discharge and gradient of hydrograph(discharge recession speed) is important for the channel formation process.channel width is able to estimated by the stable channel width theory proposed by Ikeda. In addition, it is found that the active.

River bank failure causes a heavy disaster. Many experiments had been conducted. Full-scale hydraulic experiment is very few, because of it has a limit to conduct in terms of space and budget. Therefore, many experiments were conducted in small scale and they need to be compared with the actual phenomenon. The large scale hydraulic experiment on river bank failure was conducted at Chiyoda experiment flume in 2008. We conducted small scale experiments on river bank failure and examined the reproducibility of the small scale experiments by comparison with the Chiyoda experiment. Fine-grained soil strongly influences the widening process of bank failure. In order to reproduce the results of experiment at Chiyoda experimental flume on dike failure, it is necessary to remove the fine material from the material of scaled dikes. And it is found that the time scale of widening process of bank failure follows the Froude similarity law.

It is important to clarify the formation, break and flow of river ice on frozen rivers. The aim of this study is to clarify ice break and flow phenomena during river ice breakup, as these phenomena are the initial stages of ice jam. With regard to the break of river ice, we developed a method of judging ice break by comparing the stress caused by the flowing water and flowing ice, and the allowable bending stress of the river ice. The ice flow is expressed using the continuity equation that considers the change in amount of ice, and the equation of motion that considers the effect of the flowing water. This one-dimensional mathematical model showed that although there is a problem with the reproducibility of ice jam, it is possible to reproduce ice break and flow phenomena by comparing the freezing conditions from the results of the calculations, with those of aerial images of the actual river.