Development of a 2D hydrodynamic model for flood assessment and alert system for the lower Narmada basin, Gujarat (India)

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The study develops a 2D hydrodynamic model using HEC-RAS to assess flood hazards and generate inundation maps for the lower Narmada basin in Gujarat, India. The model effectively simulates flood dynamics by integrating data, i.e. digital elevation models, stream gauge data, and land use and land cover information. Results indicate strong model performance, with R² and RMSE values of 0.92 and 0.12 for calibration and 0.77 and 0.08 for validation. Approximately 326.45 km² of the basin is severely inundated during major flood events, with agriculture being most affected. The model's outputs, including depth maps, velocity maps, and water arrival time predictions, provide critical insights for flood management. Floodwaters take 110 h to reach nearby areas and 361 h to reach validation points from upstream dam releases, offering an 8-h window to alert residents of potential overflow conditions. This information is vital for early warning systems and evacuation planning.

• The case study focuses on developing a hydrodynamic model for a multi-reach criteria basis with a single outlet in the basin.

• The case study also covers details of the adjoining tributaries flow in regions filled with water frequently.

• The Hydrological Engineering Center's River Analysis System hydrodynamic model is used for inundation mapping and early warning systems, mainly relying on open-source data.

• This is the first study of the effect of flood inundation in the lower basin after the dam site reached its ultimate constructional height in 2019.

• The 2D flood assessment model was validated in a data sparse region observed dataset of water depth.