Cyclic floodplain rejuvenation of lowland rivers

After the flooding problems along the rivers Rhine and Meuse in the Netherlands in the last decade, water management authorities emphasised on the need for new flood management strategies based on dealing with the dynamics of the river systems by providing room for rivers. Moreover, these strategies have to provide opportunities for ecological rehabilitation of the river floodplains and riparian wetlands as well. One of these strategies is the cyclic floodplain rejuvenation (CFR) strategy: cyclic intervention in the morphological and ecological development of the river floodplains and secondary channels in order to maintain the flood protection levels and to mimic natural rejuvenation processes of a river by lowering the floodplains and reconstructing the lateral channels. The CFR strategy was investigated for an 80 km stretch of the Waal branch of the river Rhine in the Netherlands. A complex of models and tools was applied, including hydraulic, morphologic, vegetation and habitat models to analyse, at one hand the impact of morphological and ecological processes on the flooding risks and ecological quality of the floodplains in time and on the other hand to assess the impact of CFR measures on the flooding risks and biodiversity. Results show that room CFR measures will reduce the flooding risks significantly for several decades. In river stretches without hydraulic bottlenecks, cyclic interventions within 30 years interval are only necessary in 15% of the total floodplain area of the river Waal. Species of dynamic floodplain and river habitats will benefit from cyclic rejuvenation measures.