Journal of the Japan Society of Erosion Control Engineering, Vol.59,No.6,2007
Long term change in landslide area in Ikawa Lake catchment using aerial
photographs and GIS
Ambika DHAKAL, Satoshi TSUCHIYA and Okihiro OHSAKA
Abstract
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 195m2 /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 1997caused many new landslides, which is now in decreasing trend.
Key words:Landslide area, aerial photographs, MapInfo GIS, deforestation area,
Ohi River
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