|BwN Building Blocks||BwN Toolbox||Pilots and cases||BwN Knowledge|
At several locations along the Eastern and Western Scheldt the dike foreshore needed to be strengthened in 2009. The requirements for this D&C contract to ensure dike stability were originally focussed 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. The environmental impact of steel slag was widely challenged, mainly by action groups who claimed that the ecological effects of the large-scale application of this material, especially the effects on the flora and fauna living on this material, have not been studied completely.
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. Van Oord Dredging and Marine Contractors and the Ministry of Infrastructure and the Environment have therefore joined forces with applied research institute Deltares and GiMaRIS consulting marine researchers to design and construct an underwater ecological landscape on a scale unparalleled in the world.
The partners' approach to enriching the foreshore involved creating as much habitat variation as possible. The engineering design called for a variety of different materials, gradients and shapes to create differences in height, hiding places, and variations in the exposure to and shelter from currents and waves. To ensure flexibility, the engineers came up with a modular system of building blocks consisting of round, criss-crossed and atoll-shaped piles of stones and linear elements, all in varying sizes. Combining these building blocks made it possible to achieve more variety at a larger scale.
|Building with Nature Design||Traditional Design|
Over a technically stable foreshore design, specialized shapes of rock armour stone are created so that a modular system is obtained that creates variation on different scales.
A traditional monofunctional design compromises a plain slope created by recycled material stable against currents and wave attack, such as steel slag. The top layer is rather flat and hardly provides hiding places for organisms to settle or recover. The result is a low overall bio-density and a limited landscape variability.
General Project Description
Title: Eastern Scheldt 'Ecodesign Structures'
Location: The Netherlands, Zeelandbrug close to Zierikzee
Date: start (2009) - end (2010)
Initiator: Ministry of Infrastructure and the Environment
Contractors: Deltares, Gimaris and Van Oord
Abstract: In this project the design of the foreshore strengthening has been enriched by placing amour 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.
Topics: habitat enrichment, ecology-fish/shellfish, building of nature.
The primary aim of the underwater landscape 'Ecodesign Structures' is to enable a quick recovery of the underwater ecosystem after the dike strengthening works.
The design is based on ecological principles, which call for a variety of materials, gradients and shapes to create differences in height, hiding places, and variations in exposure to and shelter from currents and waves.
To ensure flexibility, engineers came up with a modular system of building blocks consisting of round, criss-crossed and atoll-shaped piles of stones and linear elements, all in varying sizes. Different combinations of these building blocks made it possible to achieve variety at a larger scale. In the final landscape plan, the combined building blocks produced delineated spaces and areas that will gradually fill with fine sediment. Adding extra alternative materials to these spaces in the future will turn them into valuable new habitats.
The recovery and ecological value of these ‘Ecodesign Structures’ has been documented by voluntary divers. They report the presence of the rare lumpfish (Cyclopterus lumpus) and seahorse (Hippocampus hippocampus).
Instead of ecosystem degradation due to a traditional design, new opportunities arise with the chosen design. If divers come from abroad to dive here, it must be possible for local entrepreneurs to make money out of this. Moreover, the concept can be exported to other countries.
In addition to the 'Ecodesign Structures', three steel structures have been placed at the planning site. They are meant to support the 'Sepia Project', a project to protect the Sepia that enter the Eastern Scheldt in spring to mate.
In response to the public interest to respect the diving spot, Rijkswaterstaat financed the pro-active design. Information panels make the public aware of the vulnerable ecosystem present under water. The larger the support group, the more prominent the issue will be on the political agenda.
Planning and Design
Public interest, especially of the foundation 'Stichting de Oosterschelde' and diving clubs, raised awareness of the importance of the diving spot at the Zeelandbrug. Taking this into account Rijkswaterstaat agreed on the 'Ecodesign Structures' underwater landscape to enable fast ecological recovery and to enrich the ecosystem.
Deltares, Gimaris and Van Oord thought out a technically and economically feasible, effective and ecologically responsible solution, as ideas handed in by the divers, which combined soft and hard substrate, were economically not feasible.
BBecause 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 Schledt provides for shelter and breeding conditions. Wave attack on the foreshore can powerful. That is why the foreshore needs 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.
The design stimulates ecological functions. The diverse morphology creates a wide range of velocities. Velocity and morphology are important factors for the settlement of benthic organisms. Some can stand a high velocity better than others. Moreover, some organisms tend to avoid competition and rather adapt to another niche provided, which means that a range of different conditions is ecologically important. The material armourstone creates caves of different sizes and shapes, such that also prey-predator strategies vary widely. The tide accounts for a lot of variation in velocities and wet-dry transitions, and irregular paddles remain during low tide. Migration processes are also encouraged by the tide and the structure stimulates migration. Generally, a wide variety of niches is obtained, which enables the organisms to settle, breed, grow, hide and hunt.
The project can be seen as a no-regret, because the risk is low. The ecological condition of the Zeelandbrug with the traditional foreshore strengthening could hardly deteriorate. Yet, the goals for the 'Ecodesign' were ambitious: maximum biodiversity at minimum costs. Pilot research must reveal which shapes have the highest benefit/cost ratio in terms of ecological value. The design has to be economically and technically feasible, including maintenance and monitoring. Because the money spent will support the tourist sector, the costs can be seen as an investment.
Before the tender was issued, the ecological value of the Eastern Scheldt was already recognized. Following the 'Building with Nature' principles, the contractor had pro-actively indicated the possibilities to create additional value for underwater habitat development.
After discussing the project with various stakeholders, the Ministry recognised that the ecological value of the locations chosen could not be ignored and that it was possible to achieve a win-win situation.
After the contract was awarded, Van Oord and the Ministry investigated the options for nature conservation within the project context. The Ministry called in Deltares and GiMaRIS for advice, and the two organisations ran a workshop for a large group of stakeholders, among which several diving clubs, the aquaculture sector and even protest groups like the 'Stichting De Oosterschelde'.
Special engineering process
The engineering process was highly innovative not only because of the exceptional aim that had been identified, but also because of the way the various parties interacted. Ecologists from Deltares and GiMaRIS optimised the ecological aspect of the engineering design, while Van Oord kept a close eye on the technical feasibility. The Ministry looked at what could be accomplished within the relevant contract and budgetary constraints. Creative input from all four partners made it possible to optimise every aspect of the design, from biology to costs and technical realisation.
As stated before, the engineering design called for a variety of different materials, gradients and shapes to create differences in height, hiding places, and variations in the exposure to and shelter from the current. To ensure flexibility, the engineers came up with a modular system of building blocks consisting of round, criss-crossed and atoll-shaped piles of stones, all with dimensions up to 23 m, and linear elements up to 60 m long. Combining these building blocks made it possible to achieve variety at a larger scale.
Filling delineated spaces
In the final landscape plan, the combined building blocks give rise to delineated spaces and areas that may gradually fill with fine sediment. Extra alternative materials will be introduced tentatively into these spaces to see whether they can be turned into valuable new habitats. In this way several options to stimulate ecological processes can be investigated and evaluated from different perspectives (financial, ecological, attractiveness to divers, short-term and long-term, etc.).
Operation and Maintenance
The technical design meets the requirements for safety, obviously the main objective of the dike and forseshore 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. The risk of uncontrolled and undesired natural development is not an issue here, since nature development is the primary objective of the landscape. Of course it is interesting to compare the newly developed ecosystem with that in a conventional dike foot landscape. Rijkswaterstaat will include this in the monitoring campaigns out for the entire project. Furthermore, 'Stichting Anemoon' has started a voluntary monitoring campaign enabling divers to upload their photos for ecological monitoring.
The ecological design was not required by the client, Rijkswaterstaat. Moreover, the material used for the dike strengthening at Zeelandbrug received some negative publicity. By involving the stakeholders and interdisciplinary experts a feasible design approach could be found. Technical and ecological feasibility could be taken into account right from the beginning. On top of this, tendering procedures had to be adjusted to enable this ecologically effective and feasible design to be implemented.
To succeed with the project, the Forming interdisciplinary specialisms was essential to the project’s success. Moreover, several publications made the public aware of the principles of habitat enrichment and how the 'Ecodesign Structures' contribute to this and create added value.
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 succesfully been brought into position.
The development of the underwater ecosystem is monitored by divers, who take photographs at the marking stones. A rapid recovery was observed as well as a high biodiversity. Also rare organisms (see general description) appear to have settled within the landscape.
The following lessons were learned from this project:
- Think pro-actively. Even if habitat enhancement is not required by law, it may produce an added value that justifies the investment.
- Authorities responsible for flood safety are not responsible for other uses of dikes and foreshores, other than that they may not negatively influence the flood protection function. Designs made from this single perspective may be less suitable for other functions such as diverse habitat provision and recreational diving.
- Involve stakeholders in an early stage. Listen carefully to antagonists as well as protagonists and seek together for the best solution.
- Work interdisciplinary. The integration of ecology and/or geomorphology with hydraulic engineering can provide an innovative, beneficial and effective solution on the long term, integration of governance expertise improves the chances of actual implementation.
- Inform the public to enlarge well-informed support.
- The legal issues tackled and the increased awareness of underwater life may be the start of legislation to protect the underwater ecosystem. This will make budgets for underwater ecosystem development available, but it may also lead to formalisation and restricted access.
- The interdisciplinary network of government agencies, designers, contractors, ecologists and volunteering divers proved very effective and may be of use to future projects.