Dam it: Dutch bolster sea defences

Molenaar: Childhood memories

By Douglas Herbert, CNN.com Europe writer

ROTTERDAM, Netherlands (CNN) -- Half a century on, Simon Molenaar still flashes a proud smile when he recalls his father's valiance as a volunteer in the defence of Rotterdam.

Molenaar's childhood memory is not of the Nazi aerial bombardment of the city in May 1940, nor of the five-year German occupation that followed.

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Rather, the enemy Molenaar's father rallied to repel -- alongside thousands of his stalwart compatriots -- was water.

"The army put up sandbags, there were people in the streets protecting the dyke," Molenaar reminisced. "I wanted to see it and my father let me come along."

In 1953 -- 13 years after Germany's wartime onslaught -- a violent storm surge off the Netherlands' south-west coast unleashed a flood that killed more than 1,800 residents in the low-lying delta.

Molenaar, a former chemical industry worker, today gives tours of a massive storm surge barrier that went operational in 1997 on the tip of the Netherlands' Nieuwe Waterweg, or New Waterway.

The barrier is a legacy of a major flood-prevention programme called the Delta Plan, undertaken after 1953.

Engineers fortified dykes and bolstered other water defences against a future disaster.

In addition to the New Waterway barrier, the Eastern Scheldt barrier was opened in 1986 to help protect residents around the ports of Antwerp and Rotterdam without choking commerce.

But experts say the challenges confronting Dutch engineers are far from over, as global warming pushes water levels inexorably higher.

Already, 60 percent of the land in the Netherlands lies an average of 3.5 metres below sea level, making Dutch water management at times akin to wringing water from an insatiable sponge.

"What we expect will happen is that there will be a rise in the sea level of 20 to 25 centimetres in the next 50 years," said Harman Dijk, of the Rijkswaterstaat, a national ministry created in 1798 to battle the rising waters.

"It's not a big deal at the moment, but we don't want it to be a big deal in the future," Dijk said. "So we are making plans to prevent the Netherlands from flooding again."

Alongside the anticipated rise in sea levels, Dijk said, the country's land is predicted to sink by about 40 centimetres over the same period -- resulting in a potential net rise in water levels of up to 65 centimetres over the next half-century.

Henk Saeijs, a professor of water quality policy at Erasmus University in Rotterdam, says the trend is no less alarming when viewed over a longer timeframe.

Sea levels around the Netherlands, Saeijs said, rose by an average of 60 centimetres in the last century, a substantial increase from the 20-centimetre average rise recorded in each previous century over the past 1,000 years.

At the same time, the land itself sank by about 60 centimetres in the last century -- a trend abetted by urban engineers who have pumped water out of the country's peat to create drier conditions for building.

Dijk says the current network of dykes is built to withstand a surge of 15,000 cubic centimetres of water per second.

That is sufficient, he said, to fend off the maximum discharge of 13,000 cubic metres of water per second that the Rhine -- one of four major rivers in the Netherlands -- could churn up in a violent storm surge.

Engineers say the current system of dykes can withstand floods of a type that occur once every 100 to 400 years, while the storm surge barriers provide additional protection against a more freakish deluge occurring once every 1,000 to 4,000 years.

The massive storm surge barrier at the tip of the Netherlands' New Waterway is almost as long as the Eiffel Tower is high, and weighs about four times as much.

If a storm surge were to raise water levels by 3.2 metres or more above Amsterdam mean level -- the nationwide standard for flood watchers -- the barrier's two giant retaining walls would be swiveled on massive ball joints into the New Waterway, sealing off a 360-metre width of water.

Molenaar said the New Waterway barrier, built at a cost of 840 million Dutch guilders ($324.8 million), protects about one million people living inside Rotterdam and on its immediate outskirts.

Engineers predict they will only have to close the barrier once every 10 years under current conditions. But in the future they expect more frequent closures -- perhaps at five-year intervals -- as water levels rise.

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Dutch Ministry of Transport, Public Works and Water Management
Waterland
Environmental Defense: Dams Around the World
IISI Worldsteel:The New Waterway Storm Surge Barrier

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