Numerical simulation on a tremendous debris flow caused by Typhoon Morakot in the Jiaopu Stream,Taiwan

In August 2009, Typhoon Morakot brought a large amount of rainfall with both high intensity and long duration to a vast area of Taiwan. Unfortunately, this resulted in a catastrophic landslide in Hsiaolin Village, Taiwan. Meanwhile, large amounts of landslides were formed in the Jiaopu Stream watershed near the southeast part of the Hsiaolin Village. The Hsiaolin Village access road (Provincial Highway No. 21 and Bridge No. 8) was completely destroyed by the landslide and consequent debris flow. The major scope of this study is to apply a debris flow model to simulate the disaster caused by the debris flow that occurred in the Jiaopu Stream during Typhoon Morakot. According to the interviews with local residents, this study applied the destruction time of Bridge No. 8 and Chen’s house to verify the numerical debris flow model. By the spatial rainfall distributions information, the numerical simulations of the debris flow are conducted in two stages. In the first stage (before the landslide-dam failure), the elevation of the debris flow and the corresponding potential damages toward residential properties were investigated. In the second stage (after the landslidedam failure), comparisons of simulation results between the longitudinal and cross profiles of the Jiaopu Stream were performed using topographic maps and satellite imagery. In summary, applications of the adopted numerical debris flow model have shown positive impact on supporting better understanding of the occurrence and movement of debris flow processes.