Evaluation of erosion vulnerability for river levee material using physicochemical properties of soil focusing on torrential rainfall due to climate change

摘要

Recently, the occurrence of natural disaster due to climate change has beenincreasing. Hurricane Katrina which occurred on August, 2005 caused severe damage to someareas in New Orleans leading to collapse of sea dike and river levee. The collapse of river levee iscaused by the overtopping and then river levee material is easily eroded by flowing water on theriver levee. Recently, the numbers of torrential rainfall have markedly been increasing in Japan.Those increasing frequency of heavy rainfall also induced collapse on the river levee in Niigataprefecture on July, 2004 and the effective assessment the vulnerability of erosion is paramount.Erosion mechanism caused by overtopping and boiling depends on physico-chemical soilproperties of soil such as liquid limit, natural water content, grain size, soil particle density andcohesion. This study made an attempt to evaluate the vulnerability of erosion of some river leveematerials by using these soil properties and to propose a method for evaluating the vulnerability ofriver levee material. It is indicated from these evaluations that the river levee materials in Kantoarea are stronger ageinst erosion than those in Kyusyu area. The results are demonstrated on themaps of the evaluated vulnerability of erosion and the method of countermeasure against theclimate change induced damage in therepresentative river levees in Japan were proposed.