[H-GM02] Geomorphology

[HGM02-P04] Topographic Features of Shallow Landslides around the Medieval Mountain Castle Sites –A Case of Heavy Rainfall in Hiroshima City in 2014–

*Taiyo Kajita¹, Tsuyoshi Hattanji², Takuro Ogura³, Doshida Syoji⁴, Takahisa Furuichi⁵, Tanaka Yasushi⁶ (1.Graduate School of Science and Technology, University of Tsukuba, 2.Faculty of Life and Environmental Sciences, University of Tsukuba, 3.Graduate School of Education, Hyogo University of Teacher Education, 4.National Research Institute of Fire and Disaster, 5.Forestry and Forest Products Research Institute, 6.Faculty of Letters, Komazawa University)

Keywords:artificially modified topography, heritage, slope hazard, land fill, LIDAR

Heavy rainfall on August 20, 2014 caused many shallow landslides in granite mountains in Asaminami and Asakita districts of Hiroshima city, Hiroshima Prefecture, Japan. The medieval mountain castle sites are located on the granite mountains where shallow landslides densely occurred. This study focused on topographic features of shallow landslides around the two medieval mountain castle sites. Topographic features of a total of 66 landslides were analyzed by using the 1-m DEM before and after the disaster. The area of the castle sites was identified with survey maps of the castle sites reported by local historian, and the landslides were classified based on their location in relation to the castle structure. There are three landslides including the part of the castle sites, two of which had larger depths (3.1-3.2 m) at the castle sites area and another had a smaller depth (1.8 m). In this case, the depth of landslides depend on the structure of the original castle sites. There were two landslides where valley-like artificial structures called hori within those source areas, both of which had very large depths (3.5-7.9 m). The cause of the relatively deeper landslides was artificial movement of debris during the construction and use of the castle structures, and the concentration of water due to the modification of topography and subsurface structures. For the seven landslide cases that contained castle sites except for hori within the source area, their topographic attributes were almost same as those of landslides on natural slope, suggesting that the contribution from castle sites was small in this case.