# GIS-Based Flood Assessment Using Hydraulic Modeling and Open Source Data: An Example of Application
## 3 Results
### Hydraulic Modeling
For instance, at ST32, water elevation increases from 138.9 m in S1 to 140.19 m in S4, while at ST1, the increase is from 112.27 m in S1 to 113.31 m in S4;
* flow area increases significantly with discharge as well. At ST32, the flow area expands from 14.21 m\({}^{2}\) in S1 to 67.43 m\({}^{2}\) in S4, while at ST1, it grows from 4.08 m\({}^{2}\) in S1 to 37.12 m\({}^{2}\) in S4;
* Froude number (Froude # Chl) varies but not linearly with discharge. Overall, the values remain relatively constant across most scenarios, with a slight upward trend at higher discharges. The water depth varies depending on the analyzed flow rate, increasing progressively from scenario S1 (low flow) to scenario S4 (maximum flow). For example, in ST32, the water depth increases from 1.23 m (S1) to 2.52 m (S4), indicating a doubling of the initial value. The same trend is observed in section 23, where the water depth increases from 1.36 m (S1) to 2.56 m (S4). In certain sections, such as section 15, the water depth shows negative values for S1 (\(-\)0.47 m), indicating an area with a higher bed level where the minimum flow is insufficient to cover the entire section. On the other hand, in sections such as 10 and 11, the depth varies between 1.55 m (S1) and 2.49 m (S4), showing a steady increase in water level as the flow increases. Additionally, in sections with greater variations, such as 30 and 29, the increase in water depth is more pronounced, reaching 3.02 m (S4) in section 30. Conversely, in the upper areas of the profile, such as section 1, the maximum depth reaches only 1.51 m (S4). This analysis clearly shows that sectors with variable geometry are more susceptible to significant variations in water depth, which may indicate a higher risk of flooding under extreme flow conditions. Mapping the results of hydraulic modeling is not just a visualization tool but also a critical element for sustainable water resource planning and management, disaster prevention, and the protection of infrastructure and communities. The use of this tool contributes to better preparedness and adaptation to increasing hydrological risks. Figure 8 compares two specific areas (Zone 1 and Zone 2) along the Cigher River, analyzed under the four different discharge scenarios (S1-S4). This image is used to visualize the effects of varying discharges on these zones and to assess flood extent and the river's hydraulic behavior. In scenario S1, the flow rate is reduced, and the water is largely confined to the riverbed without causing extensive flooding. The surrounding land has higher altitudes and is not affected by floods. In scenario S2, an increase in flow rate leads to a slight expansion of the area covered by water, which begins to exceed the minor riverbed; however, the flooding remains controlled. In scenario S3, the higher flow rate results in more extensive flooding, with water inundating areas adjacent to the river, showing a larger coverage of the land by water. In scenario S4, the maximum flow rate causes severe flooding, with water covering a large part of the floodplain, indicating that scenario S4 represents the maximum risk conditions for this area. Figure 8: The hydraulic behavior of the Cigher River: A comparison of flood extent in different scenarios (S1–S4).