The collapse of caldera walls of Mt. Bawakaraeng on 26th of March 2004 in South Sulawesi is one of the largest mass movements in the history of Indonesia. The collapsed material, calculated at approximately 232 million m3, covers 8 km of the upstream part of Jeneberang River. The main purpose of this research is to evaluate the magnitude of the impact on the change of basin and how the impact decreases over time. A given amount of rainfall produces less discharge after the collapse and peak flows which normally occurred in the months of January are now found in the months of March. Before the collapse, every daily amount of rainfall corresponds to 0.6 value of daily discharge, though in 2006, it decreased to 0.45. Daily discharges are mostly low flows (less than 5 mm/day) except in the year of the collapse (2004). After the collapse, medium flows occurred more frequently and high flows (flow of over 90 mm/day) occurred in less frequency and lower values. Analysis of turbidity and discharge relationship at Bili]bili Dam located 31 km downstream of the collapse may be applied to understand the sediment exhaustion and the basin's potential rates of recovery. Bili]bili Dam's maximum turbidity rate increased significantly from 407 Nephelometric Turbidity Units (NTU) to 125,159 NTU after the collapse and turbidity's respond to discharge alters after the collapse. Peak turbidity rates normally fall faster than the discharge falling limb; nonetheless after the collapse, both values fall by approximately 50% daily.


Key wordsFBawakaraeng, change of basin, Jeneberang River, Bili]bili Dam, turbidity