Planning and Design
Because the Eastern Scheldt is so famous for diving, the underwater life is well-documented. Especially the Deltaworks provide an interesting habitat to organisms preferring a hard substrate. Wave attack on the foreshore can be powerful, hence soft sediment is not suitable as construction material. ‘Ecoreef’ structures can withstand present design conditions and offer shelter and breeding space for different species. By using ‘ecoreef’ structures for foreshore strengthening, the project combines educational, ecological and touristic functions, i.e. people, planet and profit are served.
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.
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.
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 partners’ approach to enriching the foreshore involved creating as much habitat variation as possible. The 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.
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 armour stone 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.
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 with dimensions up to 23 m, and linear elements up to 60 m long. Combining these Concepts made it possible to achieve variety at a larger scale.
In the final landscape plan, the combined modular system produced delineated spaces and areas that will 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.).
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).
Stakeholder and tender strategies
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.