JWSS - Journal of Water and Soil Science

Today, the preparation of flood zoning maps is one of the basic and important issues in the study of development projects in the world; it is considered before any investment by the related organizations. In this paper, flood zoning was performed using the two-dimensional model HEC-RAS and GIS in order to assess the risk of the construction of a railway station near the bank of the Iranshahr River, in a range of 2500 meters. Two-dimensional hydraulic application could create a more accurate flow pattern in comparison to the one-dimensional model used in the previous studies, especially in the flood plain areas. In this paper, due to the important role of the topography of the area in ensuring the accuracy of the calculation, a Digital Elevation Model (DEM) was used with very high precision (about 2 meters), as obtained from aerial photos. The results of this study indicated the onrush of flood, depth and flow velocity in different return periods. Based on the comparison of water surface profiles in the floodplains with the return period of 100 and 25 years, the maximum difference between the water levels was 0.5 m, which seemed to be reasonable by considering the low slope of the studied area. The results of this paper, therefore, showed that the location of the railway station was in medium risk and the outskirt of floodplain.

Hydrodynamic models proposed for simulating flow hydraulic in rivers assume the flow in one direction and simulate the hydraulic parameters based on the one-dimensional Saint-Venant equations. In this research, a two-dimensional HEC-RAS model was used to simulate the flow in the Karun River, between Mollasani and Farsiat stations. Geographic information system (GIS) and river cross sections were used to prepare the altitude map using the satellite image of the study area. Modeling results in river bends showed that the maximum velocity occurred in the outer bend, which coincided with the flow mechanism in the bends. Based on the results, grid type and density have little effect on flow depth modeling. However, the characteristics of the mesh used had a great influence on the velocity distribution, so that the regular high-density mesh had the best accuracy in simulating the flow velocity. Statistical analysis showed that the RMSE for the flow discharge and flow depth were 17.95 m³/s and 0.05 m, respectively. In addition, the Nash–Sutcliffe efficiency index was calculated to be above 0.9 for the discharge and flow depth, which could be considered as a desirable value.