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The Galgeplaat is a large tidal flat in the Eastern Scheldt with a surface area of 950 hectares. The construction of the storm-surge barrier in 1985 disturbed the equilibrium between sedimentation and erosion. The Galgeplaat has already lost an area of about 50 hectares and its average height has decreased by more than 30 cm.

Approach

More than 130,000 m³ of sand was deposited in an experimental approach on the Galgeplaat in 2008. New methods were used to reduce turbidity during dredging and deposition. The idea was that the wind and waves would slowly spread the sand so that the surrounding ecosystems on or near the bed would be disturbed as little as possible.

Design

The nourishment operation on the Galgeplaat was designed in a circular pattern. A protective bund of sand approximately 1 m high was built first, forming a ring with a diameter of 450 m. This ring was filled with sand during the flood phase of the tidal cycle and spread by bulldozers during the ebb phase. This allowed for the controlled construction of the nourishment location, preventing an increase in the concentration of suspended matter that would have had an adverse effect on commercial mussel beds in the vicinity.

Outcome

Traditional approaches are effective from a technical perspective but they provide less control over the spreading of fines than the new approach with the circular protective bunds. In practice, most of the sand did remain in place, and the benthic ecosystem has now largely recovered.

Partners

  • Deep sand extraction and ecosystem-based landscaping 30

    Wageningen University and Research

  • Oyster reefs 2

    NIOZ

  • Deep sand extraction and ecosystem-based landscaping 10

    Deltares

  • Deep sand extraction and ecosystem-based landscaping 26

    TU Delft

  • Deep sand extraction and ecosystem-based landscaping 24

    Rijkswaterstaat