Dam breach due to the earthquake, Land sliding inside the dam reservoir, dam overtopping as a result of intense precipitation in a watershed are examples of dangerous risks which flood caused by any of them should be predicted by suitable hydraulic or numerical models in the framework of a risk management plan. In the present research, 2DHec-Ras model has been applied in order to flood modeling of Sattarkhan dam. This dam is in the North West of Iran, located 15 km from the west of Ahar city, in the East Azerbaijan province, Iran. The downstream part of the dam to Ahar city has been studied considering the population and infrastructures in this district according to two different scenarios of dam failure. The first scenario includes piping of flow and dam failure profile with steep side walls while the second scenario consists of inclined sidewalls in the dam breach profile and overtopping of flow as the main cause of breaching. The population centers have been selected in the downstream area of dam according to the field facts. The maximum flood depth reaches up to 9.1 m for the first scenario and 7.1 m for the second scenario at the Islamic Azad University and Tabriz-Ahar road, respectively. The results show the notable risk for some of the population centers in the downstream of the dam. Furthermore, the arrival time of flood, recession time, and maximum velocities in the targeted areas for preparing emergency action plans has been calculated.

The Enhanced HLLC scheme as a robust approximate Riemann solver is used for numerical modeling of three different test cases of mobile bed and stepped mobile bed in dam failure and dam overtopping conditions. The current research has been done in the frame of the finite volume method using shallow water equations along with the Exner equation for sediment continuity. The Ribberink, Wong and Parker formulations have been used for the modelling of bed load movement. A convenient approach based on the Boussinesq hypothesis is deployed for considering turbulence effects in the second case. The affections of stepped and slope condition for the flow bed are considered through a corrected version of the HLLC flux components. Finally, the model is applied for modelling overtopping in the third case. The results of the present model are relatively reasonable by comparing with the experimental data.