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 Building with Nature Guideline > Projects > Eastern Scheldt dike foreshore ecological upgrading, NL

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Eastern Scheldt dike foreshore ecological upgrading, NL

Location: Zeelandbrug close to Zierikzee, The Netherlands,

Date: 2009 - 2010
Involved parties
: Ministry of Infrastructure and the Environment (Rijkswaterstaat), Deltares, GiMaRIS and Van Oord
Technology Readiness Level
: 7 (successful pilot case)

Environment: Estuaries

Keywords: Habitat enrichment, Ecology, Fish/Shellfish

Building with Nature designTraditional design


Over a technically stable foreshore design, specialized shapes of rock armour stone are created so that a modular system is obtained, creating variation on different scales. Generally, a wide variety of niches is obtained, which enables the organisms to settle, breed, grow, hide and hunt.


A traditional mono-functional design compromises a plain slope stability, created by recycled material, against currents and wave attack, such as steel slag. The top layer is flat and hardly provides places for organisms to settle or recover. The result is a low overall bio density and a limited landscape variability.

 

In this project, the design of the foreshore strengthening has been enriched by placing armour stone in different shapes and depths. The variety of habitats improves the ecological conditions around the 'Zeelandbrug', one of the most important recreational diving sites of Northwest Europe. 

 

Initiation Phase

At several locations along the Eastern and Western Scheldt, the dike foreshore needed to be strengthened in 2009. The tender requirements for this D&C contract to ensure dike stability were originally focused on economic aspects only. This lead to a straight, technical design, making use of the relatively cheap and technically effective material steel slag, a stone-like residue of steel production. Notwithstanding the fact that from the point of view of environmental protection law there was no necessity to adjust the technical design, the special ecological value of two locations in the Eastern Scheldt was recognized by the Contractor. 

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Planning and Design Phase

Because the Eastern Scheldt is so famous for diving, the underwater life is well-documented. Many photographs record the former condition. Especially the Deltaworks provide an interesting habitat to organisms preferring a hard substrate. Due to its natural characteristics, the Eastern Scheldt provides for shelter and breeding conditions. Wave attack on the foreshore can be powerful. That is why the foreshore needed strengthening and soft sediment is not a suitable material to work with here. The 'Ecoreef' structures for ecological development can withstand the present design conditions. The project combines educational, ecological and touristic functions, i.e. people, planet and profit are served. 

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Construction phase

Van Oord was the contractor responsible for the execution of the project. The design was made digitally visible for the crane operator on the dredger, which enabled him to accurately place the armour stones bucket by bucket, despite the prevailing currents. After placement of the material, a bathymetric survey demonstrated that elements had successfully been brought into position.


Operation and maintenance

The technical design meets the requirements for safety, obviously the main objective of the dike and foreshore strengthening works. Flood safety provided by the structure can be assessed in the future following standard procedures. For the ecological aspects, maintenance requirements in the sense of engineering interventions is not necessary for the underwater landscape.  

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Lessons Learned

The following lessons were learned from this project:

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References

http://cml.leiden.edu/students/about/oosterschelde-biodiversity.html

 

 

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