Comparison of 1D, coupled 1D–2D, and 2D shallow water numerical modeling for dam-break flow analysis of Way-Ela dam, Indonesia

Abstract

This study analyzes the flood inundation area using shallow water numerical modeling with HEC-RAS 6.3 software by comparing 1D, coupled 1D–2D, and 2D approaches. As a case study, the 2013 Way-Ela dam-break event in Indonesia is selected. Way-Ela Dam naturally formed by landslides in 2012, collapsed due to a piping mechanism after a heavy rainfall event. To estimate the breach outflow hydrograph, an empirical parametric model based on regression formula is used. Compared with the observed data, the numerical results show the 2D model produces the most accurate results among others, with reasonable computational time, while the 1D model, despite being computationally very efficient, misinterprets the flood extent map. The coupled 1D–2D model produces results similar to that of the 2D model; however, this coupled approach, which is expected to be more computationally efficient than the 2D one, interestingly yields a significantly longer calculation time. Some possible reasons are thus discussed. Additionally, comparisons for the water level and velocity are also presented in several locations to point out the difference between each model. Our finding informs the selection of an appropriate hydrodynamic model for dam-break simulations, balancing the result accuracy and computational cost.