2017 年 69 巻 6 号 p. 3-14
This paper examines the efficiency of an index derived from a distributed landslide conceptual model (DLCM) at demonstrating the influence of rainstorms on shallow landslides compared with two other indices : the soil-water index (SWI) and antecedent precipitation index (API). SWI is derived from a three-layer tank model, and its absolute value is defined as the sum of the water depths in each tank. API is used for estimating the influence of antecedent precipitation on landslides based on the half-life period. Both of these indices have been applied widely and used for an early warning system in Japan. The validity and efficiency of both have been confirmed based on many actual operations. The DLCM is based on the vertical and shallow lateral infiltration flow due to three-dimensional topography, and a safety factor is estimated using infinite slope stability analysis. The calculation of the vertical infiltration flow in this model is incorporated into the concept of the half-life period in API. The index derived from this model shows the temporal fluctuation of an unstable area. The three indices were applied to the western area (approximately 10 ㎢) of Izu-Oshima Island, Tokyo, Japan, where typhoons Wipha (2013) and Ida (1958) caused severe sediment disasters. The comparison of the index derived from the DLCM with other two indices gave the following results : Result 1 : The very strong positive correlation between the DLCM-derived index and two other indices was confirmed, supporting the efficiency of this index. Result 2 : Applying the DLCM index to the early warning system, the official announcement of a sediment disaster alarm would be set to the occurrence and disappearance time of an unstable area. This methodology is simpler than the current early warning system in Japan.
