# A Practical Approach on Reducing the Flood Impact: A Case Study from Romania
## 2 Study Area and Data Series
### Methods
The flow paths, banks, channels, and cross-sections necessary for obtaining the flood model have been exported from GIS to HEC-RAS. The terrain model limitations are represented by the resolution (the higher the resolution, the more precise a simulation is) and the absence of some elements, like vegetation, that can influence the flow direction. Still, the flood band offers an important overview of what buildings and terrains are affected. The main advantages of the HEC-RAS are the following:  
* It is an open-source software [45; 46];
* It has the same capabilities as any other software, which is not free of charge [45];
* It has proven its performance in implementing different scenarios worldwide [46];
* It can be used for forecasting [45];
* It is intuitive and easy to learn [46];
* Its internal GIS viewer presents compatibility with other GIS packages [46];
* Is faster when modeling large systems and permits a more precise computation [46]. The main limitations of the HEC-RAS are the following:  
* Users may find numerical instability problems during unsteady analyses [45; 46];
* The quality of terrain data (in terms of both resolution and accuracy) is essential in creating a detailed and accurate hydraulic model [46];
* In 2D, boundary conditions can only be added at the outer edge of the computation mesh [47];
* Lateral coupling in HEC-RAS 2D is currently a somewhat manual and limited process [46];
* Spatially distributed rainfall cannot be added, and infiltration/evaporation cannot be modeled [47]. ArcMap a component of the ArcGIS suite, was employed to construct flood hazard maps for a 1% exceedance probability for the two scenarios and damage quantification. ArcScene was used to generate 3D maps, and HEC-RAS was utilized to model the flood and incorporate embankments that were absent in the standard Digital Terrain Model [48]. The calibration was carried out by comparing the surface of the flooded zone frominundatii.ro with that obtained by the authors in the first scenario. The model was also calibrated by adjusting the roughness coefficient (Manning's coefficient) [49] available in HEC-RAS, considering the terrain features such as floodplains, meadows, rocks, sand, and various soil types. Sensitivity analysis is utilized to determine the variation of the model's output when varying different parameters [50; 51]. Simulations with various flow values were carried out to see how the flood band expands. This way, we could compare the flooded surfaces with a probability of return of 2%, 5%, or 10%. Comparison of this research and the maps provided by inundation.ro show the following:  
* The bridge's opening was considered constant for building the maps available on the site (the same as in our Scenario 1);
* On the website (Scenario 1), the water depth ranges from 2 to 5 m. For example, the thalweg has around 4 to 5 m for a 100-year return period %, almost equivalent to the present study, where the depth for 1% is 4 to 4.5 m;
* Upstream, the flooded surfaces are similar in Scenarios 1 and 2 (Figure 6). Downstream, the two flood bands differ due to different lengths of the embankments. Besides the two scenarios from Figure 6, for the intermediary case one only short comments will be made in the next chapter.