A Method for Assessing Spatial Patterns of Rainfall-Intensity Duration Thresholds for Shallow Landslides

Thursday, 18 December 2014
Reiko Akiyama1, Atsuhiko Kinoshita1, Taro Uchida2, Teruyoshi Takahara1 and Tadanori Ishizuka1, (1)PWRI Public Works Research Institute, Tsukuba, Japan, (2)National Institute for Land and Infrastructure Management, Tsukuba, Japan
It is important to predict time of landslide occurrence for mitigation of landslide disasters. Several physically-based models have been applied for assessing spatial pattern of landslide susceptibility. However, it is still difficult to predict both time and location of landslide occurrence using physically-based model. A new model which is called “idH-SLIDER” (revised H-SLIDER for assessing rainfall intensity duration thresholds.) has been proposed to assess the time and location of landslide occurrence. We combine a hillslope hydrology model proposed by Rosso et al.,[2006] and infinite slope stability analysis to assess rainfall intensity duration thresholds for each grid. The hillslope hydrology is modeled by coupling the conservation of mass of soil water with the Darcy’s law used to describe a seepage flow. Application of this model can be derived from rainfall event in 21.July, 2009 in Hofu city, Japan. Several parameters, including soil depth, geometry and etc. are composed of our detailed field survey. By integrating the field survey data and the collected rainfall data, it is possible to calculate rainfall intensity duration thresholds. There are: (1) It is realizable to set an appropriate value for cohesion of soil and reproduce the time and location of shallow landslide during the rainfall event. (2) Only few grid cells where observed rainfall data exceeded our calculated rainfall intensity duration thresholds. It has been proved by calculating the rainfall data of last 37 years. (3) Those results integrate with the historical landslide patterns evaluated by aerial photograph interpretation. And the result could be matched ultimately.(4) In result of sensitive analysis of soil thickness and soil mechanical and hydraulic parameters, it is clarified that condition of soil thickness is thicker or soil cohesion is weaker generated missing ratio increasing. According to these results, the method which has been proposed is suitable for reproducing the spatial pattern of rainfall intensity threshold and predictable time and location of shallow landslides triggered rainfall with rainfall data and few parameters.