Process of Levee Breach by Overflow at the Full Scale Chiyoda Experimental Channel

The increased occurrence of storm disasters caused by typhoons and local downpours in recent years has given rise to concerns over the possibility of large-scale floods resulting from river overflow. Levee breaches cause particularly severe damage, and in Japan, more than 80% of such accidents in the past have been attributed to overflow. Previous studies on overflow-induced levee breaches have not revealed the mechanisms of these issues on a full-scale 3D basis (i.e., side-overflow taking river flow on the riverside land into consideration). It is important to clarify these mechanisms in terms of disaster prevention and for the purpose of bringing progress in future studies on overflow-induced failure. Levees (levee crown width is 3m in 2010 and 6m in 2011, levee height is 3m, levee length is 80m) were built in the Chiyoda Experimental Channel (full-scale experimental channel; width is 30m, length is 1,300m, maximum discharge is 170t/s) in Hokkaido Japan, and a three-dimensional experiment on levee breach by overflow. The findings of the experiment are as follows: After the beginning of overflow, levee breach widening did not begin until after most of the levee section had collapsed. And in case of 6m of the levee crown width, that time in becomes long. It was also considered that, even if overflow occurred, extremely serious damage (e.g., sudden increase in levee breach width and overflow discharge) was unlikely unless the majority of the levee section collapsed.