Combined basin-scale and decentralized flood risk assessment: a methodological approach for preliminary flood risk assessment

Abstract

In this study, we focused on a combined basin-scale and decentralized (localized) approach (municipalities) to riverine flood risk mapping and assessment in the Gidra River Basin (Slovakia). The methodology applies direct spatial and probabilistic relation among the physical processes of riverine flooding with a given vulnerability. Flood hazard mapping at basin scale was based on ungauged conditions. First, we calculated the design peak discharges using the 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 Hydrologic Engineering Center´s River Analysis System (HEC-RAS) hydraulic modelling. The modelled flood extent, flow depth, and velocity were considered as hazard indicators. The results were expressed in terms of flood hazard (FHI), vulnerability (FVI), and risk index (FRI): the highest values were obtained for municipalities located in the northern-central part of the investigated area. The proposed methodology can constitute a conceptual basis for updating the Preliminary Flood Risk Assessment (PFRA) in Slovakia.