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

The Interreg IVB North Sea Region Programme

The authors are solely responsible for the content of this report. Material included herein does not represent the opinion of the European Community, and the European Community is not responsible for any use that might be made of it.
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Project description

This pilot project realized in the frame of TIDE includes a feasibility study on the restoration of a dike foreland in Werderland (Bremen, Niederbüren). The foreland restoration is planned to be partly realized as a compensation measure after national environmental law for coming main dike reinforcements at Weser and Lesum (right bank). According to present knowledge, the expected compensation requirements due to the necessary reinforcement measures are not claiming the entire potential project area (Figure 2). In terms of sustainability and effective use of available resources and means, the study however aimed at developing an overall concept suitable to be realized in partial steps.

The study development can be described as iterative process with the involvement of a stakeholder group consisting of client (SUBV), water management, nature conservation and federal waterways administrations (NLWKN, WSV) as well as dyke and nature conservation associations (BUND Bremen).
The following development targets were defined for the potential project area:
  • Functional development of tidal floodplains with focus on fish fauna (especially migrating species like Sea lamprey (Petromyzon marinus) and European river lamprey (Lampetra fluviatilis)
  • Development of typical estuarine, tidally influenced foreland habitats (shallow water zones, flooding pools and fresh water mudflats, alluvial forests and reeds)
  • Highest possible enhancement in terms of nature conservation according to guidelines on impact regulation after nature protection law for the federal state of Bremen (UNIVERSITÄT HANNOVER, INSTITUT FÜR LANDSCHAFTSPFLEGE UND NATURSCHUTZ 2011)
  • Long term functionality with low maintenance effort
After analyzing the present situation, evaluating other comparable compensation measures (e.g. Vorder- und Hinterwerder) and discussing the constructional and technical boundary conditions, six development scenarios were deduced. The main differences between these scenarios are:
  • Extent of shallow water zone
  • Composition of water regime (contact period between shallow water zone on project area and river and height of overflow barriers)
  • Percentages of aimed at habitats (shallow water zone, mudflats and reeds)
As a result, a preferential scenario and a sub scenario were specified. The preferential scenario (Figure 3) includes the lowering of bank reinforcements over a length of 350 m (-2.42 m MHWL). Furthermore, a subplot of the project area on a ground level up to 1.35 m above sea level is prepared in order to promote long term establishment of fresh water mudflats and a 2 ha shallow water zone as habitat with various functions to the benefit of fish fauna (spawning, residence, resting, overwintering) is created. The contact period between river Weser and shallow water area comprises 4.5 hours per tidal cycle. The mudflat areas at the outer border of the project area adjacent to the river Weser are flooded approximately 8 hours per tidal cycle.
Plantings are only intended on a small scale in order to promote spontaneous development. Initial plantings of softwood species in the north of the project area will be compared to an unplanted area to the south. The observation of both areas is expected to allow general conclusions on the effectiveness of initial plantings.
In order to protect the main dike of the river Weser, a line of willow plantings is used to catch flotsam. As a co-benefit, the decomposing flotsam promotes structure diversity in favor of insects and small animals.
The remaining area not affected by alteration and profiling activities is left to natural succession. Mowing or grazing is not foreseen.
The preferential scenario can be implemented in partial steps.
The sub scenario (Figure 4) comprises the removal of bank reinforcement and the installation of an additional overflow barrier.
The study ends with estimating the enhancement potential according to the guidelines on impact regulation after nature protection law for the federal state of Bremen. Even more crucial than this habitat related assessment is the expected functional benefit in view of adjacent Natura 2000 sites.
The study results are principally applicable to comparable projects in the fresh water zone of the Weser estuary and other estuaries of the North Sea region.

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Report: Management measures analysis and comparison