# GIS-Based Flood Assessment Using Hydraulic Modeling and Open Source Data: An Example of Application
## 3 Results
### Hydraulic Modeling  
The following section details the hydraulic modeling procedure used in this study. Figure 5 presents the longitudinal profile of the analyzed section of the Cigher River, illustrating the variation in elevation as a function of distance for different flow scenarios (S1-S4) and associated critical levels. The \"EG\" lines (energy line) and \"WS\" lines (water surface) show how energy and water levels vary in each scenario, highlighting critical points. The dotted lines indicate critical levels, which are useful for assessing flood risks or hydraulic issues. As flow increases, the \"WS\" and \"EG\" levels rise, indicating greater energy but also increased risks of erosion and flooding. The \"ground\" line marks the terrain elevation for comparison with water levels. Figure 5: Longitudinal profile of the Cigher River and elevation variations for different flow scenarios; (**a**) the longitudinal profile of the riverbed, showing the elevation along the main channel; (**b**) elevation variation along the river for different flow scenarios (S1–S4), where WS S1–S4 represents water surface levels under different hydraulic conditions and the blue color symbolizes the water level in the first scenario. Figure 6 illustrates in 3D the 32 cross-sections (ST) of the Cigher River section, represented in the four scenarios (S1--S4) and grouped into segments (ST 1--8, ST 9--16, ST 17--24, and ST 25--32). From Figure 6, a progressive increase in water level and the area covered by water can be observed from S1 to S4, with high-flow scenarios (S3 and S4) indicating complete filling of the riverbed. The upstream segments (ST 25--32) have a smaller cross-sectional area and transport capacity compared to the downstream segments (ST 1--8), where the river is deeper and wider. This representation underscores the need for monitoring to prevent exceeding maximum capacity, particularly in narrower or shallower areas, and highlights how flow rates influence the river's capacity under various scenarios. Figure 7 provides visual representations of some cross-sections along the analyzed river segment (representative examples). These illustrations serve as useful tools for understanding the spatial distribution of key parameters and improving the assessment of river behavior. Figure 6: A 3D analysis of the river’s longitudinal profile under different hydraulic scenarios. The figure shows variations in the riverbed and bank geometry across different cross-sections (ST 1–32) and scenarios (S1–S4). The green lines represent the bank station limits, while the cyan-blue areas indicate the extent of the water surface under different flow conditions. The red points in the images (Figure 7) indicate locations on both the left and right banks of the river, offering insights into the river's geometry and morphology. Additionally, the blue color represents the water level in S1, providing a clear visualization of the  
Figure 7: Examples of cross-sections in different scenarios, highlighting hydraulic and morphological variations (STx—cross-section; S1–S4—hydraulic scenario; WS—water surface; EG—energy grade line; “ground”—terrain elevation; “bank station” indicates reference points located on the riveranks). hydraulic profile of the river at various points along the analyzed segment. The solid lines represent the water level according to the four generated scenarios. In Figure 7, the images on the right depict water velocity. It is observed that the highest values are located in the central part of the profile sections, specifically in the Thalweg area. The comparative analysis of parameters across the four scenarios reveals the following:  
* water velocity (Vel Chnl) increases consistently from S1 to S4 as the discharge increases. For example, at ST32, velocity rises from 0.56 m s\({}^{-1}\) in S1 to 1.11 m s\({}^{-1}\) in S4, while at ST1, the increase is even more pronounced, from 1.96 m s\({}^{-1}\) in S1 to 2.53 m s\({}^{-1}\) in S4;
* water level (W.S. Elev) increases with each scenario due to the rising discharge.