Sediment]related disasters in Southern Kyusyu caused by an extreme rainstorm
in July 2006
Osamu SHIMIZU Takashi JITOUSONO
Abstract
During July 2006, a heavy rain in excess of 1,000 mm was recorded over a five]day
period with about 400 mm of maximum daily rainfall in the area where Kagoshima,
Miyazaki and Kumamoto prefectures are close to each other. This is the largest
rainstorm event in this area in the 31]year rainfall record. Due to this rain
many small collapses, 101 to 102 m3 in collapsed sediment, were widespread in
the whole area; and a small number of slope failures, 103 m3 in collapsed sediment,
also occurred and three of them killed three people in northern Kagoshima. Besides,
a deep]seated landslide that yielded ten to twenty thousand m3 of sediment occurred
in Izumi. This is the largest of all mass]movement events by this rain. Major
sediment disasters that overtook this area and/or the vicinity during the last
fifteen years demonstrate that landslides greater than the Izumi's slide by one
to two orders of magnitude were often triggered by rainfall less than this rainstorm.
Thus we conclude that magnitude of sediment movement caused by this rainstorm
was considerably small in spite of the newly established record of rainfall.