Combined basin-scale and decentralized flood risk assessment. A methodological approach for preliminary flood risk assessment

In this study, we focused on a combined basin-scale and decentralized approach (municipalities) to riverine flood risk mapping and assessment in the Gidra River Basin (Slovakia). The methodology applies a direct spatial and probabilistic relation among the physical processes of riverine flooding with a given vulnerability. First, we calculated the design peak discharges using a rainfall generation model and rainfall-runoff model–in particular, the Stochastic Rainfall Generator (STORAGE) and the Continuous Simulation Model for Small and Ungauged Basins (COSMO4SUB). After that, we used the obtained flood scenarios for hydraulic modelling with the Hydrologic Engineering Center’s River Analysis System (HEC-RAS). The modelled flood extent, flow depth, and flow velocity were considered hazard indicators. The results were expressed in terms of a flood hazard index (FHI), flood vulnerability index (FVI), and flood risk index (FRI): the highest values were obtained for municipalities located in the northern-central part of the investigated area.