DAM BREAK ANALYSIS USING TWO DIFFERENT MODELS

Abstract

Dam break analysis is a study conducted by assuming a hypothetical dam break failure to estimate the potential flood hazard that would result downstream of the dam. In this study, two well-known models have been employed, namely, the MIKE11 and the HEC-RAS to simulate hypothetical dam break failure scenarios of the Bhavanisagar dam which is located in Erode district of Tamil Nadu State, South of India. This analysis is useful to assess different dam failure models to mark the potential inundation areas for planning emergency evacuation measures downstream of the dam. These two models showed a variation in their simulations as the result of using different numerical solution schemes for flood routing in the downstream reach of the dam. Therefore, the performance evaluation of the dam failure models is carried out by comparing the flood wave and its features simulated using these models. MIKE11 and HEC-RAS models were subjected to the same input conditions and also have identical breach shape (trapezoidal), the size and time to failure of the breach. The channel routing was carried out using the one-dimensional Saint Venent equations. The overtopping failure mode was adopted by taking the final breach elevation above the dead storage level. The salient characteristics of the flood hydrographs simulated at different locations downstream of Bhavaisagar dam are compared with each model simulations to understand the variation through the relative performances, such as breach flow, peak discharge, maximum water level, time of occurrence and attenuation ratio etc. The outflow hydrographs estimated immediately below the dam by these two models are different, with the HEC-RAS model discharges being higher in the rising and falling part of the hydrograph immediately after the peak is reached. But the simulated time to peak discharge of outflow hydrographs estimated immediately below the failed dam nearly remain the same for both the models simulations. The peak elevation profile of the HEC-RAS simulations which tracks the peak elevations reached along the downstream of the breached dam shows a relatively higher flood elevations than the corresponding profile given by the MIKE11 model.