The mechanism of three-dimensional levee breach by overflow (i.e., lateral overflow with consideration of river flow riverside land) has not been clarified in past studies. Elucidation of this mechanism is very important for disaster prevention as well as for the future progress of studies on levee breach by overflow. We conducted experiments of levee breach in three-dimensions by overflow using the Chiyoda Experimental Channel. The results of the experiment are as follows: Until the beginning of levee breach, phenomena near overflow area was similar to one by front overflow. It means that we can apply knowledge from anamnestic levee breach experiment involving front overflow to until the beginning of levee breach. After the beginning of levee breach, it related to unit width discharge and levee breach speed.

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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.

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