Flood inundation mapping in small and ungauged basins: Sensitivity analysis using the EBA4SUB and HEC-RAS modeling approach

Abstract

Flood mapping is an important part of flood risk analysis and management as its result is the visualization of flood hazard in terms of flood depth and extent. However, flood mapping strongly depends on the selected modeling approach. Furthermore, model input data usually incorporate uncertainties that may vary significantly in time and space. In this study, the EBA4SUB (Event-Based Approach for Small and Ungauged Basins) hydrologic model and the one-dimensional HEC-RAS (Hydrologic Engineering Center's River Analysis System) hydraulic model were selected for evaluating their sensitivity, in terms of simulated flood area (FA) and volume (FV), to different combinations of input parameters. Results of hydrologic modeling highlight the great variation of design peak discharges which strongly influence the modeled FA and FV. The sensitivity of FA and FV to excess rainfall determination was several times larger than the sensitivity to the routing propagation for two assumed gross rainfall distributions (rectangular and Chicago), which highlights the importance of the correct estimation of soil and land use properties affecting the infiltration estimation. Moreover, the sensitivity of FA and FV to the roughness parameter was 1.5-2 times greater than the sensitivity to the cross-section parameter, yet, stressing the importance of input parameters for hydraulic modeling.