Flood Risk in Rivers: Climate Driven or Morphological Adjustment

Flooding remains one of the major natural disasters that threatens human lives and property. Flood management has taken a new look, whereby flood risk in rivers is now viewed as driven by not just climate change but also by river channel morphological adjustment which have been overlooked in the past. This study aimed at evaluating the contributions of channel morphological adjustment to flood risk in rivers using river Elbe in Germany as a case study. To achieve this, an inundation model for the June 2013 flood event was developed using the LISFLOOD-FP model. A total of thirteen additional flood inundation models were ran at varying scenarios of river width, bed elevation and channel friction coefficient under a fixed discharge series. The results of these simulations revealed that, variability in river channel morphology constitutes an integral part of flood risk in rivers, hence a complementary driving factor to flood risk in addition to climate change. Thus, the assumption of a constant river channel morphology during flood modelling should consequently be open to question for flood hazard management. Flood frequency analysis for the Elbe basin was also presented. Discharge data spanning an interrupted period of 61 years (1958-2018) from 10 gauges along river Elbe were analysed for various return periods. It was concluded that any discharge rate having a return period of 5 years (2544 m(3)/s) and more would likely exceed the water carrying capacity of the Elbe river. The study proposes potential measures for effective flood modelling in rivers and can also serve as important tool for informing and supporting environment related decision making in flood risk management, land use regulation and floodplain management in the study area.