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 The rejuvenation strategy led to a diverse floodplain vegetation distribution that largely complies to the historical reference for the Waal River.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.

Mapping Vegetation Density in a Heterogeneous River Floodplain Ecosystem Using Pointable CHRIS/PROBA Data

“…Concomitantly, these newly developed river floodplains also serve as nature restoration areas, where succession of vegetation leads to highly valued ecosystems [9]. However, floodplain vegetation causes resistance to the water flow within the river floodplains [10]. Because of the complex structure of floodplain vegetation and the accumulation of material caused by sedimentation processes, flood flow velocities decrease and the water surface increases during flooding events [11].…”

The temporal and social dimensions of river rehabilitation: towards a multi-dimensional research perspective.

“…Outcomes of such processes are highly predictable, since cyclic processes or dynamic equilibria by definition return to their starting point or fluctuate around an attractor. This strong belief in cyclicity as the main guiding principle can also be observed in many river rehabilitation approaches (e.g., Baptist et al 2004;Smits et al 2000a;Vera 1997). In these approaches,`cyclicity' is regarded as an indispensable management concept.…”

River, delta and coastal morphological response accounting for biological dynamics

“…Biomorphodynamic stochastic and deterministic models have been recently developed, but most of these models (Brookes et al 2000, 2004, Hooke et al 2005 do not take into account the active role of vegetation and, in turn, the effects of morphological changes on the vegetation growth. Recently, Corenblit et al (2007) introduced a "fluvial biogeomorphic succession" concept, coupling landform and riparian vegetation evolution in bi-directional modelling.…”