Flood inundation mapping in small and ungauged basins: sensitivity analysis using the EBA4SUB and HEC-RAS modeling approach Matej Vojtek, Andrea Petroselli, Jana Vojteková and Shahla Asgharinia 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. Matej Vojtek (corresponding author) Jana Vojteková Department of Geography and Regional Development, Faculty of Natural Sciences, Constantine the Philosopher University in Nitra, Nitra, Slovakia E-mail: mvojtek@ukf.sk Andrea Petroselli Department of Economics, Engineering, Society and Business Organization (DEIM), Tuscia University, Viterbo, Italy Shahla Asgharinia Department of Innovation in Biological, Agro-food and Forest Systems (DIBAF), Tuscia University, Viterbo, Italy Key words | EBA4SUB, flood, HEC-RAS, inundation, sensitivity analysis, ungauged basin INTRODUCTION Flood mapping is a crucial element of flood risk manage- ment since it provides the delineation of flood depth and extent in flood-prone areas. The creation of flood maps is usually performed using a combination of hydrologic and hydraulic models that is particularly challenging in case of small and ungauged basins where the calibration of advanced hydrologic models is difficult due to lack of observed discharge data (Grimaldi et al. a; Szymczak & Kre ˛ z ˙ alek ). In order to estimate the design peak dis- charge or the design hydrograph for ungauged basins, different hydrologic models are usually applied (Petroselli et al. ). In particular, simple conceptual models rep- resent a reliable compromise between the physical representation of the investigated hydrologic processes and the limited number of adopted parameters (Mlyn ´ski et al. ). Regarding the hydraulic part, the first important issue concerns the selection of the modeling approach to be used which mainly depends on the objective of the study and flow conditions. In general, one-dimensional (1D) and two-dimensional (2D) hydraulic models are commonly used allowing the simulation of steady or unsteady flow. 1D models consider discrete cross-section profiles for defin- ing the channel and floodplain shape and assume that water moves only longitudinally along the river direction. How- ever, the limitation of 1D hydraulic models is that they are not able to provide information on the character and direc- tion of flow as well as the way of flowing off the obstacles. 1002 © IWA Publishing 2019 Hydrology Research | 50.4 | 2019 doi: 10.2166/nh.2019.163 Downloaded from https://iwaponline.com/hr/article-pdf/50/4/1002/584667/nh0501002.pdf by guest on 06 June 2020