Topographical features of slopes with deep-seated landslides occurred by heavy rainfall at July 2018 in Tajikawa river basin, Otoyo, Kochi, Japan

Abstract

More than twenty deep-seated landslides occurred by the heavy rainfall in July 2018 in Tajikawa river basin at Otoyo, Kochi, Japan. They destroyed a bridge of an express highway and gave much damage to local roads and river structures while gave no damage to human lives. Micro-topographic features in the slopes with the landslides were examined by field investigation and LiDAR DEM with 1 m resolution. It was revealed that the landslide at 2018 occurred within an old landslide and other old landslides near the ridge existed above the landslides at 2018. Fresh cracks and steps were identified just above the upper boundary of the landslides at 2018. These cracks and steps might have been generated due to the reactivation of the old landslides near the ridge by the rainfall.