Vogels en rivierdynamiek: Welke perspectieven biedt natuurontwikkeling langs de rivieren?

In order to cope with exceptional peak discharges in the river Rhine and avoid further dike-construction works, scenarios to enlarge the winterbed of the river are currently being investigated. These do not only address the purpose of safety, but also allow ecological rehabilitation of some of the original river dynamics. Ecological rehabilitation is included in the targets concerning management policies along the rivers Meuse and Rhine and their tributaries. One of the measures to achieve a larger winterbed includes artificial lowering of the forelands. In two already artificially lowered floodplain areas along the river Rhine (Wall), an extensive study was carried out to monitor the ecological effects of the measures in a series of drier and wetter years. This paper discusses some of the effects to be expected when floodplains in the winterbed are subject to more dynamic water tables. It is clearly demonstrated that waterbirds and waterside birds (e.g. waders, gulls) may profit from the generally wetter conditions in the lowest parts of the floodplain and/or in years with higher discharges (Tab. 1, Figs. 4-8). On the other hand, both feeding and nesting conditions (particularly for ground-nesting terrestrial birds) may become far less favourable and some characteristic and scarse birds of less dynamic riverine landscapes (e.g. Corncrake, Corn Bunting) may even go extinct as a result of the measures. If widening the winterbed by lowering the floodplain level will be the only way to assure safety in the Dutch river area, compensation for losses of important natural values should be offered outside the floodplain, behind the dikes. Here, ground-level is often lower than in the floodplain in the actual winterbed, and thus opportunities exist to establish compensation areas.