Although levees are breached in the backwater reach as well as in the normal flow reach and the damage resulting from a levee breach in the backwater reach of the main river can be as serious as that in the main river itself, few studies on the levee breach in the backwater reach has been conducted. Accordingly, we collected data of levee breaches in the backwater reach that occurred in recent years, classified the collected breaches into two types according to the direction of flooding water flowing out of the breached section and examined characteristics of each of the types and mechanism of widening of the levee breach opening in the backwater reach.
