A CASE STUDY ON OLD RIVERBED AND DISASTER BY EA RTHQUAKE AND INUNDATION

Abstract

 This paper is a case study about the Yahagi river basin, the greater part of which is located in the granite area. Hence, the sandy ground is dominated over the riverbeds and the alluvial lowlands along the Yahagi river. The sandy ground along the old Yahagi riverbeds had attacked by liquefaction during the past earthquakes, followed by their larger damages. Also, the old riverbeds and hinter-lowlands are easily suffered by inundation due to heavy rains.
 In this study, the old riverbeds and hinter-lowlands in the Yahagi river basin were picked up and analyzed through literatures and investigations, together with discussing their formation processes, and examining the disaster damages by liquefaction and inundation. As the results, it was found that, although the overflow risk from the main course of Yahagi river has been mitigated due to lowering the riverbed, countermeasures against drainage behind levees on tributary rivers became important issue. Moreover, the dangerous locations in detail due to earthquake and inundation were revealed, together with pointing out that the disaster danger area was increasing alon g with land development, and also the retarding basins are required along the area of old riverbeds and old hinter-lowlands in the Yahagi river basin.