Assessment of flood hazards due to overtopping and piping in Dalaman Akkopru Dam, employing both shallow water flow and diffusive wave equations

Abstract

This study was carried out to determine flood propagation using shallow water equations (SWEs) and diffusive wave equations (DWEs) to reveal how the flood modeling results differ in terms of flow depth, flow velocity, and hazard level. The solution methods were tested based on the hypothetical failure of the Dalaman Akkopru Dam resulting from two failure mechanisms: overtopping (OT) and piping (PP). A 2D hydraulic model was constructed using HEC-RAS to determine the propagation of flood waves due to the failure of the dam by the mechanisms selected. Froehlich equations were applied to predict the breaching parameters of the dam. After calibration, the hydraulic model was run to determine the possible flooding magnitude in the towns of Ortaca, Dalaman, and Dalyan. The flood arrival times, maximum flow depths, flow velocities, and hazard classes were obtained for the Dalaman, Ortaca, and Dalyan city centers, and the Dalaman International Airport from the hydraulic model results. The modeling results showed that the inundated area is similar for both the SWEs and DWEs solutions, while the flow depth and velocity results are significantly different due to the neglected convective acceleration terms of the SWEs when deriving the DWEs. Considering the modeling results, even though the DWEs provide a computational cost advantage, the reliability of the solutions should be examined against the SWEs. Hazard maps were generated for both solution methods and failure mechanisms. The results revealed that most of the settlements in the basin have H5 and H6 hazard classes with a high risk of structural damage. Therefore, the installation of early warning systems and evacuation of district centers were suggested as mitigation measures. A feasible evacuation plan for the neighborhoods, taking into account the flood arrival time of the failure scenarios, is needed.