Interpretation of Flood Zone Mapping using HEC-RAS Hydraulic Model for the Bennihalla Stream through 1D Flow Analysis

Abstract

Food hazard research has since been important in the last two decades and continues to be relevant in future climate scenarios to develop realistic solutions to disaster risk. For more detailed and accurate outputs, studies on flood hazards are conducted through simulations using high-resolution digital elevation models (DEMs). It is very essential to provide more accurate maps to analyse the flood prone region by selecting suitable best input data which is nothing but the DEMs. The study utilizes daily maximum discharge data were collected from 2003 to 2020, where in 2007 peak flood of 3174 m3/s has been occurred which resulted heavy flood inundated area. In this study for the maximum flow has been used and integrating the Shuttle Radar Topography Mission (SRTM) and Cartosat Digital Elevation Model (DEM) as input for flood-zone mapping using the HEC-RAS tool. By simulating various scenarios using HEC-RAS, the study anticipates significant outputs, including flood extent predictions, water surface profiles, and submergence areas for different return periods. The regression analysis showed that both the SRTM and Cartosat models have high R-squared values, indicating a good fit. The SRTM model has a slightly higher R-squared value (0.867) compared to the Cartosat model (0.838), suggesting that it explains more of the variance in flow area. In terms of velocity, both models show a significant negative relationship with flow area, with the SRTM model exhibiting a stronger influence. The Cartosat model demonstrates a significant positive relationship between top width and flow area, unlike the SRTM model. Correlation analysis corroborates these findings, with the Cartosat DEM showing a significant positive correlation between top width and flow area. The Cartosat DEM also shows lower RMSE (1158.42) and MAE (910.32) values compared to the SRTM DEM, indicating more accurate predictions of stream flow. Paired t-tests indicated no significant difference in water surface elevation (W.S.Elev) and Froude number (Fr no) between the two DEMs. However, a significant difference was found in energy grade elevation (E.G.Elev), suggesting discrepancies in capturing this parameter. There was no strong evidence of a difference in top width (Top Width Act), although the result was near the threshold of significance. The analysis highlights the importance of DEM resolution in hydrological modeling. The Cartosat DEM's higher resolution contributes to its superior performance, capturing significant variations in stream flow related to elevation changes more accurately than the SRTM DEM. Based on the lower error metrics and stronger model coefficients, the Cartosat DEM is recommended for stream flow analysis in this study. The detailed flood hazard maps generated from this study will be instrumental in developing effective flood management strategies for the Bennihalla River, thereby mitigating the recurrent threat to the local villages.