Assessment of the effects of cyclic floodplain rejuvenation on flood levels and biodiversity along the Rhine river

Abstract

To reduce flood risks in the Netherlands, measures to increase the flood conveyance capacity of the Rhine River will be implemented. These measures will provide more room for the river and include lowering of the floodplains and excavation of secondary channels. Moreover, these measures provide opportunities for ecological rehabilitation of the floodplains. However, it is expected that floodplain sedimentation and softwood forest development in rehabilitated floodplains will gradually reduce the conveyance capacity and the biodiversity. Therefore, a floodplain management strategy was proposed that would meet both flood protection and nature rehabilitation objectives. This strategy, Cyclic Floodplain Rejuvenation (CFR), aims at mimicking the effects of channel migration by removal of softwood forests, by lowering floodplains or by (re)constructing secondary channels. In this study, the effects of CFR measures on reducing flood levels and enhancing biodiversity along the Waal River were assessed. A one-dimensional hydraulic modelling system was applied together with rule-based models for floodplain vegetation succession and floodplain sedimentation. The model simulations demonstrated that the flood management strategy of Cyclic Floodplain Rejuvenation is able to sustain safe flood levels in the Waal River when about 15% of the total floodplain area is rejuvenated with a return period of 25 to 35 years. The rejuvenation strategy led to a diverse floodplain vegetation distribution that largely complies to the historical reference for the Waal River. Cyclic Floodplain Rejuvenation may be the appropriate answer to solve the dilemma between flood protection and nature rehabilitation in highly regulated rivers. © 2004 John Wiley and Sons, Ltd.