Analysis for a Landslide Dam Outburst Flood in Ambon Island, Indonesia

Abstract

In July 2012, a landslide dam subsequent to the large-scale collapse of a mountain edifice occurred on Ambon Island in the eastern part of Indonesia. A height of the dam was approximately 140 m and a volume of dammed water was approximately 250 million m 3 . The dam failed about a year after its formation in July 2013, and a large-scale flood wreaked havoc on the downstream area. In this disaster, the information on the topographic changes before and after the dam failure was obtained from digital maps (DEM) based on satellite images and field measurement. Furthermore, field surveys examined the various conditions of the sites around the landslide dam and a process of the outburst flood was recorded on video. Simulation of a landslide dam outburst flood was conducted using LADOF model that reproduces the process of overflow and erosion of a landslide dam outbreak and the calculation result was verified by field measurement data. The results are as follows. (1)The peak flow rate of the landslide dam outburst flood determined by simulation was approximately 17,000 m 3 /s. (2)The occurrence and duration of the flood, longitudinal profile of the dam, inundated area and flow depth obtained from the simulation almost agree with the actual results obtained from field measurement. (3)The phenomena whereby the progress of longitudinal erosion caused the collapse of the stream bank and rapidly expanded the river channel width could be confirmed by analysis of the video images.