Journal of the Japan Society of Erosion Control Engineering,
Vol.57,No.3,,2004
Reconnaissance of the gigantic landslide occurred on Mt. Bawakaraeng in the south Sulawesi state of Indonesia and unstable debris sedimentation (prompt report)
Satoshi TSUCHIYA, Syozo KOGA, Katsuo SASAHARA, Munehiro MATSUI, Mitsuo NAKAHIRO, Humito WATANABE, Hironao SHIMA, Kazuhisa YOSHIDA
Abstract
A gigantic landslide occurred on the caldera wall of Mt. Bawakaraeng (2830m) located in the uppermost reach of the Jeneberang River in South Sulawesi, Indonesia, on March 26, 2004. The huge mass of debris yielded from the gigantic landslide of Mt Bawakasraeng traveled about 7km down the upper reach of the Jeneberang River with 500 m to 800 m in width. Ten persons were killed and 22 others were unaccounted for in the accident. Twelve houses and one school were crushed or buried in the debris, and the damage was expected to run into around 2,214 million Rp. The volume of the slide mass caused by gigantic landslide is estimated at about 240 million cubic meters with a head width of 1,600 m, a height to 700 m to 800 m, and a thick of approximately 200 m. The other hand, the debris deposit has a totally volume of 272 million cubic meters on the upper reach of Jeneberang River, and 160 million cubic meters deposited within the caldera. The main cause of the landslide occurrence has been still unidentified It was the 782 mm of cumulative rainfall during March 1 to 26 before the landsliding, and any earthquakes were not recorded around the day of occurrence, March 26. About three months have elapsed after the day of occurrence, and recorded a cumulative rainfall of 430 mm. However, there has been generated the V-shaped or U-shaped valley deepening with the size of 50m to 150m in width, 30m to 80m in depth because of these materials easily being eroded. The eroded sediment volume up to now is estimated 14 million cubic meters by the site investigation. In next rainy season, there could be a great possibility of strong erosion and huge sediment transportation with debris flows. We recommend the implementation of urgent structural counter measures, such as excavation of riverbed, rising and construction of Sabo facilities, and non-structural counter measures, for example the early warning system, and establish of hazard map.
Key words:gigantic landslide, debris flow, caldera, Sulawesi, Mt. Bawakaraeng
Japan Society of Erosion Control Engineering
Sabo Kaikan, 2-7-5 Hirakawa-cho, Chiyoda-ku,
Phone +81-3-3222-0747 Fax +81-3-3230-6759
http://www.jsece.or.jp/
Mail jimu@jsece.or.jp