A novel assessment of the role of Danube floodplains in flood hazard reduction (FEM method)

Abstract

During the last decades, river floods accounted for enormous damages especially in highly developed and/or densely populated regions worldwide. Moreover, due to anthropogenic alterations of hydrology and river morphology (climate change, land use changes in the catchment, channelling and constricting rivers) and due to the ongoing accumulation of values (such as settlements, infrastructure facilities, etc.) in flood prone areas, this amount of damages is likely to rise in future. Integrated flood risk management is legally in force and aims at reducing the negative effects of floods by combining structural and non-structural flood protection measures. Non-structural measures such as the preservation or restoration of floodplains are considered by the EU Floods Directive as an effective tool for reducing flood risks. For most of the rivers, however, very little is known about the effectiveness of floodplains in regard to hydrological and hydraulical flood hazard reduction. This lack in knowledge often obstructs the integration of these natural flood retention processes into the concepts of integrated flood risk management. In the present study, the Austrian Danube was investigated along its entire 350 km length, determining reaches and floodplains with high relevance for flood water retention and thus for reducing flood hazards downstream. A novel analysis based on one-dimensional and two-dimensional hydrodynamic-numerical modelling, using hydrological and hydraulic parameters defined under the so-called floodplain evaluation matrix method (FEM; Habersack et al. in Nat Hazards, in print, 2013), was carried out to evaluate retention effectiveness on various spatial scales. The results illustrate the magnitude and the variability of flood retention and hydraulic parameters with respect to different hydrological settings (flood wave shape, recurrence probability).