Project part-financed by the European Union (European Regional Development Fund)

The Interreg IVB North Sea Region Programme

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Vorder- und Hinterwerder

Crux of the matter

The compensation measure ‘Tidal habitat Vorder- und Hinterwerder’ is a flagship measure, because several experienced partners worked together during the planning and implementation stages, the social status of nature conservation was very strong at that time and there were no conflicting plans to be considered.
The tidal waters at Vorder- and Hinterwerder were flooded longer than projected by the hydraulic models used. To optimize future measure planning and implementation processes, the hydraulic calculations undertaken during the planning stages should be analyzed in order to improve the predictability of tidal influence on potential project areas along estuaries. This is crucial in order to estimate e.g. the degree of siltation and thus the maintenance effort to expect.
The monitoring results show that reconnecting river and floodplain by opening summer dikes is principally possible within certain limits. The opening of summer dikes initiates the development of habitats which have been in place on a large scale before the first deepening and straightening measures took place at the Weser River (e.g. intertidal habitats, shallow water areas and back waters). An essential precondition in view of developing shallow water areas was reducing the tidal range on the project area by suitable constructional measures (summer dike opening, in- and outlet structure installation). It has to be accepted that there is no permanent connection between river and polder during the entire tidal cycle.
Although the aimed at habitats were successfully developed, a lack of natural morphodynamics has to be accepted. As a consequence, certain habitats cannot exist in the long term without anthropogenic management. This concerns for example intertidal mudflats and shallow water areas which silt up and overgrow in the course of the development. Eroding forces can only be expected on a small scale. The present frame conditions (e.g. dike safety, shipping) and the small scale of measures prevent or at least restrict the recreation of natural eroding forces which contribute to preserve different habitat structures. Thus, there is development need to be stated for concepts balancing decreased tidal ranges and close-to-nature morphodynamics in a way to minimize management efforts.

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Important to know

Reports / Measures / Tools

Report: Management measures analysis and comparison