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

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