Flood Disaster along Kariyata River Caused by Heavy Rainfall on July 13, 2004, Niigata Prefecture, Central Japan-The Relation of the Current Processes of the Flood to the Landforms-

Abstract

A huge flood disaster was caused by a heavy rainfall around the Chuetsu area of Niigata Prefecture on July 13, 2004. The flood breached the levees in many places along Ikarashi-, Kariyata-, and Chigoshimizu Rivers, so that many houses were swept away and wide areas were under muddy flood water in Sanjo and Mitsuke Cities and Nakanoshima Town.In this study, we describe the damages sustained by the flood in Nakanoshima Town area and the southern area of Mitsuke City along Kariyata River, and discuss the current processes of the flood at these areas. It is clear that a surge of the flood attacked houses near by the point of levee breach at Nakanoshima Town, judging from the evidences such as the directions of scours and the traces of flood current toward the houses. The preferred orientations of inclined or fell -down houses , traffic signs, fens, etc., indicated the direction change of flood current. Though the primary surge ran powerfully toward southwest, the flood flowed westward being led to the lower topography until the direction changed toward northwest by an obstruction of natural levee. On the other hand, in the southern area of Mitsuke City, the flood current direction was restricted so much by the narrow valley plain that its flood strength increased much more. As the levee of Chigoshimizu River also breached, the older levee, which remained between the present one and fluvial terrace, was collapsed immediately. The flood current did not only lose its power when it had reached at the lowest terrace but also run up beyond the terrace and destroyed some houses standing on it.

Influence of Microtopography and Alluvial Lowland Characteristics on Location and Development of Residential Areas in the Kuji River Basin of Japan

“…Differences in the height or deposition conditions of sand gravel in a deposition plain indicates the history of floods, from which we can determine the inundation frequency or duration by classifying the MT of the plain [28]. The relationship between MT and flood damage has been researched in the field of geography, focusing on the relationship between and MT and flood records [29][30][31]. Generally, the degree of safety against flood inundation is high in slightly elevated areas such as terraces and natural levees but low in former river beds or backmarshes.…”