Ken’ichi KOSHIMIZU and Taro UCHIDA
For integrated catchment]scale sediment managements, it can be thought that the sediment yield induced by the subsequent expanding landslides due to rainfall is one of key processes. This study presents a quantitative analysis of expanding landslides by surveying the Shukushubetsu River basin, at the foot of the Hidaka mountain range in central Hokkaido, Japan. This area recorded heavy rainfall in 2003, reaching a maximum daily precipitation of 388mm. We extracted the original and expanding landslides from 1963 to 2008 using aerial photographs. As a result, we found that in the period 2003|2008 (after the heaviest rainfall in 2003), the expanding landslide area was 2.7 times larger than the original landslide area. Also, the expanding landslide rate from 2003 to 2008 is 4 times greater than that from 1963 to 2003, while the original landslide rate after the heaviest rainfall in 2003 was similar to that before the heaviest rainfall. Maximum daily precipitation from 2003 to 2008 was not much higher than that from 1963 to 2002. We also found that around 70%of expanding landslide extended to upward or side. Thus, we concluded that due to the heaviest rainfall in 2003 gave a impact on the stability around the landslide scars triggered in 2003, then these affected area was landslide during the relatively small rainfall.
Key wordsFexpanding shallow landslide, heavy rainfall, catchment]scale sediment managements, aerial photography, GIS