| Sumari: | On January 1, 2006 flash flood disaster (in Indonesia is known as banjir bandang) occurred in Putih River, Jember District of East Java Province. This disaster resulted in more than 80 people were killed and hundreds were injured. The disaster was caused by natural dam break. The natural dam was formed by landslide due to heavy rainfall. After the January 2006 disaster, new cracks and crevices were found in the upstream area of Putih River. Based on this condition, repetition of similar disaster in the future is likely to occur. Therefore, it is required to conduct mitigation efforts in order to reduce the prob-able casualties in the future. One of the mitigation efforts is conducted by simulation of the past event. The understanding of past event from the simulation result can be used as reference to arrange plan and action of mitigation efforts. Modeling simulation of the January 2006 flood was conducted by 1-D models. Flood hydrograph was approximated by using Nakayasu method. The daily rainfall data recorded from the neighboring rainfall stations were transformed to hourly rainfall data by implementing the Alternating Blok Method. The rainfall intensity was calculated using the Mononobe formula. The natural dam model was interpreted from field observation and related references. Flood hydrograph induced by dam break process was approached by modeling flow over a growing opening. Model calibration was conducted by varying roughness coefficient, height of dam and breach parameters. Two marks of maximum elevation of flood at 5.996 km (RS 6 + 984) and at 12.980 km (RS 0 + 000) downstream of the natural dam were used for control points in the model calibration. The calibration process has shown that the height of natural dam was significantly influencing to the changes of flood flow surface elevation at the control points. The result of flood simulation in reconstructing the January 2006 flood showed that the simulations are able to approximate the disaster event both for water surface elevation and the flood arrival time.
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