Dutch poised to protect New York from the sea
Four hundred years after the English explorer Henry Hudson discovered 'by chance' what is now known as Manhattan, the Dutch are returning.Henry Hudson was actually trying to find the shortest route to India, but in 2009 the Dutch have a very different mission. They want to protect the island of Manhattan, and the city of New York, from the rising sea water.
How the new sea defences would lookNew York's sea defences need major reconstruction to bring them up to the present-day standards of those in the Netherlands.
So Rotterdam City Council, the Arcadis engineering firm and Amsterdam's VU University are going to help improve matters. They have decided on a combination of a dam and a flood barrier already in use in the Netherlands.
The plans for the new sea defences in New York's Verrazano Narrows were presented last week and are expected to cost 6.5 billion dollars.
New York's present sea defences allow for major flooding once every 100 years, but defences in the Netherlands allow for such floods only once every 10,000 years.
Pete DirckeIn [pictured right] the few hundred years since New York became a metropolis, it has narrowly escaped disaster a number of times. Rising sea levels make the situation more dangerous, as do the fiercer storms which will result from climate change. If a major storm hits such a big and economically important city, the damage will be in the hundreds of millions of dollars.
Piet Dircke from Arcadis (photo © waterforum.net) illustrates the technical requirements of the new defences:
"It is after all the entrance to the Port of New York and must be able to accommodate the world's biggest ships. At the same time, you have to take care of the bay and maintain its tides for ecological reasons."
Why no dikes?
Jeroen Aerts [pictured left] from the VU University's Institute for Environmental Issues explains:
"The New York coast is enormously long. You could think about constructing dikes all the way along, but that would be hugely expensive because you'd have to start from scratch. What we are proposing is to close off all the openings to the sea with flood defences, in precisely the way it's done here in the Netherlands."
The Verrazano Narrows at 1.6 kilometres are too wide for an ordinary flood barrier, which closes off the opening to the sea with two enormous gates.
The system which has been chosen combines the properties of two sea defence systems in the Netherlands: the storm surge barrier and dam at Oosterschelde in the province of Zealand, a huge construction comprising 18 floodgates which move up and down; and the Maeslantkering storm surge barrier near Rotterdam where two enormous gates open sideways.
The plans were enthusiastically received at a recent international conference on protecting coastal cities, but they do call for an investment of USD 6.5 billion. Jeroen Aerts thinks the money will be found. He even suspects the present economic crisis could actually prove an advantage because of the number of jobs created by this sort of huge infrastructure project.
Mr Dircke also believes in the viability of the project:
"The idea that New York is in real danger has got through since Hurricane Katrina. Policy makers and those in power realise something has to be done. Our plans are very expensive, but doing nothing will end up costing even more. In the end, it's a shrewd economic investment".
The Maeslantkering barrier
This sea defence system is located in the Nieuwe Waterweg ship canal and protects Rotterdam and the surrounding area against storm surges. It comprises two enormous gates at the end of long arms. The arms are hinged to the banks. The gates are actually two floating pontoons which the arms move towards the middle of the waterway. Once in place, they fill with water and act as massive walls in the channel. When the flood risk is over, the water is pumped back out of the gates and they are moved back to the sides of the waterway. The system became operational in 1997, and has only been used once, on 8 November 2007.
The Oosterschelde barrier
This storm surge barrier in Zealand province is 9 kilometres long and comprises huge gates which sink down during major storms. This stops high water from penetrating the Oosterschelde estuary. Under normal conditions, the gates hang above the water, allowing the tide to ebb and flow. This ensures there is no ecological damage to the surrounding area, which is a national park.
Thijs Westerbeek van Eerten