FIELD SURVEY AND NUMERICAL SIMULATION OF FLUVIAL INUNDATION AND SEDIMENT DEPOSITION DUE TO DYKE BREACH OF CHIKUMA RIVER

Abstract

 Severe damage was found in the Hoyasu area, Nagano City, due to the dyke breach of the Chikuma River and its fluvial inundation and sedimentation, which deteriorated agricultural crops and the cultivated lands. Through a field survey, it is found that the deposited sediment consisted of silt and clay with fine particles, and the thickness of deposition was 20 cm or more around the breach point. Next, through numerical simulations of bed load and suspended load, the maximum flow depth and overall sediment deposition could be reproduced. However, the accuracy of the model should be more improved to predict the sediment deposition more precisely at each point. Furthermore, an assumed area map of sediment deposition was suggested by overlapping the maximum thickness of deposition calculated from several breach points.