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CityFixer

Cleaning Up Dirty Lakes With Artificial Islands

The Marker Wadden Islands in the The Netherlands will become silt traps and bird sanctuaries.

A rendering showing how the Marker Wadden Islands may appear after completion. (Courtesy Natuurmonumenten in Nederland)

Currently, The Netherlands’ most ambitious environmental project in years isn’t much to look at. Squint your eyes from the shores of the country’s Markermeer Lake right now and all you’ll see is some pumping equipment and, if you’re lucky, the odd geyser of watery mud. What’s going on here is nonetheless groundbreaking—quite literally so. That’s because in an effort to bring vitality back to this large lake just northeast of Amsterdam, The Netherlands has come up with the ingenious solution of building a string of new islands.

Called the Marker Wadden due to their aimed-for similarity to the Wadden Islands that lie just off the country’s northern coast, these islands are gradually appearing above water as I write. Their aim, which I will explain in more detail below, is to provide, across an 800-hectare (three-square-mile) site, a place to stow silt that is currently clogging up the Markermeer Lake and stifling its life. In doing so, it will simultaneously create a structure that will succeed in naturally anchoring further silt after its construction.

Construction began in April, with the first meter of dry land appearing on May 11. The main island, which will ultimately be a maze-like collection of creeks, dunes and reed beds, should be completed sometime in 2018, after which four further islands will be added. This archipelago itself with be protected by an atoll-like ring of rock breakwaters on the windward side and underwater sand dams on the other. It will also be equipped with a harbor from which the public can access walkways placed at a safe distance from the island’s future bird life.

(Google Maps)

The map above shows the Markermeer. The islands will be constructed at the top of the lake, due north of the section where the lake’s holding dam (shown in yellow) makes a sharp bend. The initial island should cost €70 million ($78.2 million) to construct and the subsequent four smaller ones €50 million ($55.8 million), while continuing to develop the islands as a thriving, protected ecosystem will cost another €225 million ($251.3 million). The funds, gathered together from the public purse and the Dutch postal lottery and overseen by state conservation body Natuurmonumenten in Nederland, may sound like a lot of money. Still, if the Netherlands didn’t do something with the Markermeer, they’d be left with a lake at the very heart of the country that was languishing half dead.

To understand the problems the lake faces you need to look back over a recent past that has seen the Netherlands radically reshape itself, greatly increasing its land mass and freshwater areas through reclamation and levee-building. The Markermeer’s history as a lake, you see, is a relatively short one. Until 1932 it formed part of the Zuiderzee, a shallow, brackish bay feeding straight into the North Sea, albeit partly sheltered by a string of islands.

In 1932, this bay was transformed into a freshwater inland lake by the construction of the Afsluitdijk Levee, a huge project that saw the two separate fingers of the country’s northern mainland joined together by a 20-mile causeway. As the bay became a lake it was renamed the Ijsselmeer, but this lake itself was partitioned further in 1975 by the creation of a huge dam. This dam sectioned off a part of the Ijsselmeer to create a new lake called the Markermeer, though to complicate matters further the section of this lake nearest to Amsterdam is for historical reasons referred to as the IJmeer.

The Markermeer as seen from the Marken Peninsula. (Jean Robert Thibault/Flickr)

The initial purpose of the dam was to parcel off a section of lake for the creation of a new polder, which would have seen the lake’s waters replaced almost entirely by dry land. The land reclamation plan was nonetheless abandoned due to public concerns that it could both destroy a vital site for migrating birds and dry out the existing land around it. Future urban development was instead concentrated on the already existing Flevopolder to the south.

Scrapping the polder plan still didn’t stop the Markermeer becoming something of an environmental mess. With the new dam in place, the lake’s wider flow was disrupted and silt built up on the lake’s bottom. By blocking out light and oxygen, this silt has disrupted the food chain, suffocating possibilities for plant life and algae and thus making it impossible for aquatic creatures and the birds who feed on them to survive in healthy numbers, starving the waters and reducing the site’s popularity for bird migration. With an average depth of just 3.6 meters, the lake has veered perilously close to becoming a sort of watery Sahara. If its ecosystem is ever to thrive, it needs to get rid of all that silt.

That’s just what they’re doing now, in a way that’s both ambitious and ingenious. The plan is to use the silt to create the Marker Wadden islands, simultaneously cleaning the water and creating a new habitat for all sorts of plant and animal life.

To do so, the island’s constructors, the company Boskalis, first created a trench on the lake bottom into which the silt can drain. From here they pump it into island-shaped forms arranged along the southern side of the dam. Here’s some footage of the first appearance of one of the islands above water, on May 11.

As the silt shown in the clip piles higher, it will push out water and the island-shaped form will gradually become land which can be contoured to create rises and creeks, with layers of coarser clay. As no major development is planned, most of the soil doesn’t need to be solid enough to take buildings, though there will be a harbor and visitor center at the site. Instead, the islands will be marshy collections of sandbars, mud flats, reed beds and shell reefs, with a shape that changes slightly depending on wind and water levels. As the islands rise, silt swirling around in the lake will settle naturally on the lee side, gradually increasing the size of the landmass while at the same time keeping the water clear.

Once the silt levels in the wider lake have fallen to a point at which mollusks can survive, the waters will become yet clearer thanks to these shellfishes’ silt filtering abilities. If all goes well, The Netherlands will be left with a cleaner, more biodiverse lake that thrives both as a bird migration spot and a watersports center, albeit one with strict no-boating zones to protect habitats.

If the plan works, a lake that was once partitioned off exclusively for land development may become a natural haven once more. As the project’s overseers caution, however, the untried nature of the approach doesn’t mean success is already in the bag. As the project’s manager told the newspaper Parool:

“We have been doing research for decades on the factors that are relevant to the IJsselmeer’s nature, and there are still things we cannot understand at all. You can press on all kinds of buttons, yet things then happen you do not expect.”

The island plan also doesn’t mean that the lake itself, at the heart of a densely populated state, will be entirely free of future development. Right now, the city of Amsterdam is in fact constructing further islands for residential use on the section of the lake that touches the city’s border, while the Flevopolder to its south houses Almere, one of the country’s fastest growing cities. Still, as the lake’s water becomes cleaner and its northern waters repopulate with aquatic plants and the animals that feed on them, The Netherlands has the chance to square intense urban development with a concern for protecting the environment. Let’s keep our fingers crossed.

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