2.3. Flood Mapping Model
One of the important criteria for risk assessment is vulnerability, which was calculated in SVA by the qualitative approach. This study tries to make the combination of the vulnerability of assets with the source of danger, which is a flood due to dam destruction. Thus, it is necessary to assume different scenarios for the dam break due to terrorist attacks and obtaining outputs. The outputs of the breaking dam were used for simulating the flood loaded on downstream lands to obtain the flood mapping, including the cross-section and velocity of the flood in the downstream floodplain area. Using HEC-RAS as open-source software that is compatible with GIS provides advantages to merge data from security sources with hydraulic and flood data. This software also allows designing culverts, bridges, side weirs, spillways even if necessary while the countermeasures are provided.
To model the flow of the flood, the boundary conditions should be introduced to HEC-RAS software. Boundary conditions (B.C) include upstream and downstream B.Cs that contain a certain flow rate and water surface balance, or water surface ramp (angel) and critical depth. Figure 7 demonstrates the simulation processes of flood mapping in HEC-RAS software and the transition of outputs to GIS.