Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

H (Human Geosciences ) » H-DS Disaster geosciences

[H-DS14] Geohazards in humid, tectonically active countries and their precursors

Mon. May 27, 2019 1:45 PM - 3:15 PM 106 (1F)

convener:Masahiro Chigira(Disaster Prevention Research Institute, Kyoto University), Hiroshi YAGI(Faculty of Art, Science and Education, Yamagata University), Satoru Kojima(Department of Civil Engineering, Gifu University), Taro Uchida(National Institute for Land and Infrastructure Management), Chairperson:Chigira Masahiro, Taro Uchida

1:45 PM - 2:00 PM

[HDS14-07] Prediction of shallow landslides and debris flow by rainstorm: dynamic hazard mapping toward disaster mitigation

*Yuki Matsushi1 (1.Disaster Prevention Research Institute, Kyoto University)

Keywords:Soil thickness, Tree roots, Pore-water pressure, Slope stability, Equivalent coefficient of friction

This study demonstrates a strategy for predicting location, timing, and magnitude of rainfall-induced shallow landslides and areas affected by subsequent debris flows. Spatial distribution of soil layers was modeled for evaluating thickness of sliding material on hillslopes, which provides a basis for predicting source area and volume of shallow landslides and simulating subsurface hydrological processes. Soil accumulation in hollows was calculated on a geographic information system using a 1 m-meshed digital terrain model with soil production by bedrock weathering and transport by soil creep. The output was validated by a ground-based survey in the actual terrain in a selected watershed. The shear strength of the bulk soil was evaluated by direct shear tests using undisturbed specimens, and quantification of soil reinforcement by tree roots through an in-situ survey at soil pits. Hydrological monitoring was carried out at representative hillslopes for modeling fluctuation in subsurface pore-water pressure by rainwater infiltration. By coupling all of those data and modeling, we analyzed the hillslope instability, and then compared the output with a landslide inventory map to confirm the accuracy and precision of the prediction. Time-series change in areas of debris flow runout was estimated based on assumed equivalent coefficient of friction as a function of hillslope wetness in the watershed. Such dynamic mapping of geohazard fills a demand in disaster mitigation in local communities for increasing events of heavy rainfall.