Evaluation of effects of rainstorm conditions on the timings of landslides occurrences based on return period

Yasuhiro SHUIN, Norifumi HOTTA and Masakazu SUZUKI


In this paper, we propose an estimation method associated with the effects of different rainstorm conditions on the timings of landslides occurrences. This method uses three-layer tank model calculating soil water index (SWI) which has been widely used in Japan in order to predict the timing of shallow landslide occurrences. The novelty of this method is due to use an each tank storage value. This method was applied to three landslides. One is shallow landslides occurred on 10 July 2010 in Shobara-city Hiroshima prefecture, and the others are deep seated landslides occurred on 6 September 2005 in Shiiba village and Misato town (former name : Saigo-village) Miyazaki prefecture. The results of this study were as follows : 1) Landslides occurred after the time when a tank storage value exceeded the past maximum storage value ; 2) In the comparison between a tank storage value and past maximum value, to use the return period (RP) of a tank storage value is valid ; 3) The difference of rainstorm conditions is able to be recognized as the difference of RP of each tank layer storage value ; 4) The timing of shallow landslides occurrence depended on the RP of the first-layer tank, and the timings of deep seated landslides depended on the RP of the second-and third-layer tanks. These results of this study suggest that it is possible to predict the timings of landslides occurrence despite differences in landslide scale.

Key words

return period, soil water index, three-layer tank model, shallow landslide, deep-seated landslide