Characteristics of rainfall-induced slope-failure distribution focused on geographical, vegetational and geological features: a preliminary case study for Japanese recent extreme events.
Abstract
A heavy-rainfall hazard occurred in Setouchi region, Japan from July 5 to 7, 2018. It was caused by a seasonal rain front followed by Typhoon Prapiroon. This rainfall induced numerous slope failures, debris flows and river flooding in a wide area of western Japan.
This study surveyed the dominant cause of slope failures in two basins in eastern Hiroshima, Japan. They are located in Seno-river basin and Kurose-river basin. In these areas, the precipitation reached 385 mm in three days, which was 1.6 times as much as the average of total precipitation in July. Locations of slope failures were visually identified in aerial photograph. A 30-m resolution digital surface model (ALOS World 3D- 30 m), vegetation distribution map and geological map provided by Japanese national institutions are analyzed to obtain geographic setting of each slope-failure site. In Seno-river basin which contains a lot of mountains, a large number of slope failures were located at >40 degrees of slope. In Kurose-river basin, those were located around 25 degrees of slope. These degrees were lower than that of previous studies. Spatial heterogeneity of long-term and frequent heavy rainfalls possibly contributes for the contrast. In both areas, high proportion of slope-failure area is identified in north-facing slopes. The slope failures were most prone to occur at natural bare field in Kurose-river basin and secondary forests in Seno-river basin. Furthermore, in the same tree species, afforestation areas caused more slope failures than natural forest areas. These results suggest that tree roots contributes for stable slope construction which prevents from slope failure. Besides, slope failure happened frequently at rhyolite and granite. Our future study combining these characteristics will contribute for integrated prediction of slope-failure distribution at upcoming extreme rainfall events in Japan.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMNH0010001N
- Keywords:
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- 1821 Floods;
- HYDROLOGY;
- 4313 Extreme events;
- NATURAL HAZARDS;
- 4333 Disaster risk analysis and assessment;
- NATURAL HAZARDS;
- 4341 Early warning systems;
- NATURAL HAZARDS