抄録
The Yosasa river of northern Totigi experienced the biggest flood disaster by the heavy rainfall, on August 26, 1998. The natural banks of the Yosasa river have special characteristics for lateral erosion, and therefore, such special phenomena occurred, that flood water seriously eroded the river banks and the width of channel became three to five times as wide as the original one. Some new channels were also formed in the event. In the occasions, numerous sands and gravels, and also tremendous drift timbers, were flushed out. In this paper, the bank erosion by the biggest flood of low frequency in the Yosasa river was studied based on the results of field survey.
