Sensitivity Analysis of the Two-Dimensional HEC-RAS Model to Governing Equations in Flood Hazard Mapping: A Case Study of Khorramabad River

Vayskarami, Iraj; Haghizadeh, Ali; Fathabadi, Aboalhasan

doi:10.22111/jneh.2025.50364.2086

Sensitivity Analysis of the Two-Dimensional HEC-RAS Model to Governing Equations in Flood Hazard Mapping: A Case Study of Khorramabad River

Document Type : Research Article

Authors

¹ Ph.D. student of Watershed Management Engineering, Department of Range and Watershed Management Engineering, Faculty of Natural Resources, Lorestan University, Khorramabad, Iran

² Associate Professor, Department of Range and Watershed Management Engineering, Faculty of Natural Resources, Lorestan University, Khorramabad, Iran

³ Associate Professor, Department of Range and Watershed Management Engineering, Faculty of Agriculture and Natural Resources, Gonbad Kavous University, Gonbad, Iran

10.22111/jneh.2025.50364.2086

Abstract

Despite significant advances in hydraulic models, the incomplete understanding of flood processes and the spatial-temporal variations of model inputs (such as topography and surface roughness) has limited the accuracy of flood predictions. In this study, the impact of computational equations on the accuracy of the HEC-RAS model in mapping flood hazard zones was examined. To this end, water flow variables for discharges of 15, 34, and 1000 cubic meters per second were simulated over a 3-kilometre stretch of the downstream river of Khorramabad. The sensitivity analysis results indicated that this model is highly sensitive to factors such as Manning's roughness coefficient, the dimensions of the computational grid, and the method used to solve the governing flow equations. Among various hydraulic properties, water surface elevation exhibited the least sensitivity to the computational equations. The model's accuracy in simulating the discharge measured in March and November 2024 was significantly better when using the wave dispersion method. Conversely, for the flood event in March 2019, the dynamic wave method yielded more accurate results. The analyses were conducted by evaluating the measured parameters (depth, velocity, and flow width) and the simulation results of four observation sections, using statistical indicators RMSE and MAPE. The results indicated that in most sections, the flood extended to the banks, and at the bridge section (Section D), greater depth and velocity were observed due to lateral constraints. Overall, when the channel cross-section has a sufficiently high capacity for the inflow discharge, the wave dispersion method is the preferred choice. Conversely, for high-recurrence discharges and in situations where the flow extends into the floodplain, the dynamic wave equations would be the superior choice.

Keywords

Main Subjects

Hydrology & Hydrogeology

References

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