Long term change in landslide area in Ikawa Lake catchment using aerial photographs and GIS

概要

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The change in the landslides largely affects the sediment yield of a mountainous catchment, however quantitative studies analyzing these changes at the scale of forested mountainous catchments still remain scarce. This paper aims to study the long-term change in the landslide area in Ikawa Lake catchment located at the upper Ohi river basin in Shizuoka Prefecture, central Japan from the year 1964 to 1997. Landslide data at the interval of about five years from 1964 to 1997 were derived from the visual interpretation of aerial photographs. The extracted data were mapped using the GIS software. The analysis showed that the year 1964 had the largest area of landslides whereas the year 1975 had the highest number of landslides. The landslides covered about 2 percent of the area of the Ikawa Lake catchment on average. The landslide area in general is in decreasing trend, the average annual rate of decrease being 195 m2 /km2. The area of a landslide becomes approximately half in about 10 years after its occurrence. The amount of continuous rainfall was found mostly related to landslide occurrence, which caused an episodic increase in landslide area. From the analysis of the aerial photograph, it was found that deforestation and road construction in the study area from 1964 to 1997 caused many new landslides, which is now in decreasing trend.
社団法人砂防学会の論文