Back analysis of debris flow in Umyeon Mountain using Flo-2D software

Abstract

Mountain areas are highly prone to debris flows, which can lead to many dangerous and destructive events. Knowledge of possible inundation areas, the thickness of deposits and the velocity of the debris flows during the debris flow event are all useful to define, especially to find any vulnerable areas and identify mitigation measures that should be taken in order to protect existing infrastructure. In order to obtain accurate and acceptable results, the input parameters must also be highly accurate. Real parameters that are suitable to characterize the involved material are the most accurate way of finding believable debris flow scenarios. Most simulations of this type are done without considering the area reduction factor (ARF), but area reduction factor is actually an important parameter to show the blockage affecting a debris flow due to the obstruction of buildings. Building obstructions might have an effect on the velocity of debris flow, impact pressure on buildings, and the overall depth of the debris flow. In this study the widely used Flo-2D model is applied. For this study, sensitivity analysis was carried out to figure out the most sensitive input rheological parameter. Extensive back analysis was performed and the results were compared with the field observed data. Among all the simulations, the one that most closely fit the occurring event was chosen. Originally, the chosen rheological parameter was used to execute the simulation without considering the area reduction factor, and then the simulation was executed a second time while considering the area reduction factor. After the simulations, the results were analyzed to check the differences in velocity, depth, area of inundation and impact pressure due to blockage of buildings. This analysis showed that results which consider the area reduction factor are more accurate and more useful for the purposes of mapping debris flow hazards, and furthermore that the modeled depths and velocities are more accurate and follow better field conditions.