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Boskalis jaarverslagen 2012

Marker Wadden: groundbreaking ecological design for restoration

In March 2016 Boskalis starts work on stage 1 of creating one of the largest nature restoration projects in western europe: the Marker Wadden. the project will transform the ecologically impoverished Markermeer into a dynamic area with a rich animal and plant life through the creation of nature islands using sand, clay and fine sediment. “Building with nature techniques play a key role in the project,” says Hendrik Postma, director at Boskalis Nederland.

Lake Markermeer was created in 1976 when the Houtrib dike between Enkhuizen and Lelystad was completed. The dike had a major impact on the underwater environment of the lake. Fine sediment that was previously carried away by the current to Lake IJsselmeer now fell to the bottom of Lake Markermeer where it settled like a blanket, making the water of the lake turbid. As a result fish and bird populations have declined dramatically over the last decades. “With the creation of the Marker Wadden we want to rebalance the ecology,” says Roel Posthoorn, Marker Wadden project director at the client, the Dutch Society for the Preservation of Nature (Natuurmonumenten). “Together the Markermeer and IJsselmeer form the largest freshwater clay lake in western Europe. At present it is just a huge lake of untamed and unused turbid water between Lelystad and Amsterdam. Over the past few years we have developed a vision to give Lake Markermeer a sustainable future, using the Dutch Wadden Area as a source of inspiration.” Thanks to a contribution from the Dutch Postcode Lottery as well as support from the national government and the provincial authority of Flevoland, Natuurmonumenten now has the opportunity to realize this vision. The Dutch Department of Public Works is responsible for the contract management.

Resonance

The ideas of Natuurmonumenten resonated with the vision of Boskalis, one of the founders of the Building with Nature philosophy. “That means that in designing shipping channels, ports or offshore wind farms we not only look at the hydraulic engineering part, but are able to include the ecological aspects right from the planning stage,” explains Postma. “By developing ecological knowledge we are better able to predict natural processes. Applying that knowledge to our designs helps us to overcome resistance and speed up the preliminary process stage.” Postma emphasizes that this approach can be applied to almost any project. “But the Marker Wadden project is a Building with Nature project par excellence. The landscape and the ecology have been given top priority from the very start. Our approach is based on the question of what provisions were needed to create a healthy habitat for plants and wildlife. Once that had been established it was then up to us, in our role of hydraulic engineer, to realize the plans. The interaction between the various parties to coordinate the wishes and practical possibilities culminated in this groundbreaking design.”

Approach

“The objective of the parties involved is to select as smart as possible an approach that focuses on the creation of a common platform and the quest for optimization and innovation. One of the innovations we are introducing on this project is ‘building with fine sediment’. This will allow us to develop a high-quality nature area using simple methods, Postma continues.” Stage 1 of the project comprises the creation of the first large island and a marshland with vegetation, shallow ponds, creeks and channels. Boskalis will construct a new area of around 300 hectares, both above and below the waterline. To protect it from storms we will construct beaches, sand banks and low dunes, linked by a rock dam. We will provide for gradual transitions from land to water, as well as creating various levels under water. This will allow the sediment to settle in shallow areas and creeks, thus creating a natural water purification system. In addition a special trench will be constructed to collect the fine sediment from Lake Markermeer. This ‘sediment trap’ will make the turbid water clear again. The captured sediment will be used to construct more islands in the future. “That is a unique aspect of this work, because the material is essentially too soft for building an island. This will be resolved by building ring dikes of sand to contain the sediment, which will then develop into a nature area. That is one of the Building with Nature applications that make this project so interesting,” says Postma.

Paradise

Posthoorn expects the Markermeer nature to stage a quick recovery. “The natural embankments will allow mussel beds to develop again. Water plants will start growing again, fish will resume their spawning and birds will return to the area,” he says. The Marker Wadden will not only be a paradise for birds and fish, but also for nature lovers. The plans provide for the construction of a yachting marina as well as long walking trails, observation posts and children’s play areas. “The preparations for the first phase are in full swing, execution will start in March 2016,” says Postma. “It will take about 12 months for the first island to rise above the waterline, after which the development can start.”

Click here to watch the animation of the Marker Wadden project.

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