Synthetic dykes: the Dutch wave of the future?

Radio Netherlands Worldwide 15 Feb 11;

Most of the Netherlands’s coastal defences consist of dykes made of large angular blocks of basalt. However, in one location, a dyke has been coated with an experimental layer of synthetic material. Not the most romantic of materials, but effective in coping with the ever-rising sea level.

The experiment is being conducted on a dyke off the coast of the province of Zeeland. For the past three years the dyke has been covered in a top layer of crushed rock mixed with a synthetic adhesive. The new type of coating is actually performing better than expected: three years of continuous wave action and severe winters featuring storms, snow and ice, have not resulted in any discernable wear.

The world famous Dutch defences against the sea have so far – let’s be honest - not been very subtle. Better protection almost invariably means higher dykes, more concrete and more asphalt. However, the sea level keeps rising, forcing the Dutch to come up with smarter ways of keeping the water out. And, if at all possible, cheap and environmentally friendly.

Huge quantities of synthetic material
As regards the latter issue – possible environmental damage – the synthetic dyke raises a number of questions: How environmentally friendly can it be to introduce large quantities of synthetic material into the environment? What if all coastal defences were covered in this material, wouldn’t that already constitute a huge amount of pollution? Johan Rasing from BASF, the German chemical company that developed the material, quickly puts paid to that notion:

“This synthetic material is a polyurethane, a completely stable product. Chemists call this type of material inert. It does not react with any other material and will not leach out. It will stay the way it is, forever.”

This in marked contrast with the concrete or asphalt currently forming the coating of the nation’s sea dykes, which will continue to leach toxic substances for many, many years. The new coating – called Elastocoast - features numerous open spaces between the pieces of crumbled rock: a veritable paradise for mussels, seaweeds and all kinds of lichen which can easily find a foothold there, and give the dyke quite a natural look.

Safe?
The real question is whether such an open structure, featuring no less than 50 percent hollow space, could ever be strong enough for a dyke. Could such a dyke ever be safe? Kees Lazolder from engineering firm Arcadis explains that it’s all about these cavities:

“Those hollow spaces are key, because the waves break on the surface and their force disappears in the cavities of the material. It is a very effective way of cushioning the impact of the wave. It extends the lifespan of the material and allows it to absorb the impact of much more powerful waves.”

Could this high-tech material possibly be applied in other parts of the World where governments simply don’t have the money to build state-of-the-art coastal defences? John Rasing and Kees Lazolder both immediately admitted that Elastocoast is slightly more expensive than either asphalt or concrete, but added that because of its long life-span might prove more economical in the long run.

Malaysia
All of the above makes the synthetic dyke a Dutch export product which can easily face the global competition. Mr Rasing has an example:

“My colleagues are currently working on a project in Malaysia which involves a total surface of 18,000 square metres. That is quite a large section, of about a kilometre-and-a-half long and 15 metres wide.”

The only serious disadvantage to the new coating is not the synthetic material, but the stone enclosed in it. According to Kees Lazolder:

“If that is not available locally, don’t even think about it. The transport costs would be prohibitive.”