(과학) 인간이 만들어 낸 세계최대 물결

출처: http://www.bbc.com/news/science-environment-34151723

11 September 2015

The world's biggest manmade wave 인간이 만들어 낸 세계최대의 물결

By Rebecca MorelleScience Correspondent, BBC News, Netherlands

Science correspondent Rebecca Morelle explains how the artificial waves are created

At the Deltares Research Institute, just outside the city of Delft in the Netherlands, engineers are carrying out the final tests on their new machine.

In a huge concrete tank, colossal wave after colossal wave crashes down with an ear-splitting roar.

This is the Delta Flume, and it can create the largest artificial waves in the world.

We had a wave of over 5m, but we're hoping to get some larger ones

Dr Bas Hofland, Deltares

"Yesterday, we had a wave of over 5m, but we're hoping to get some larger ones," Dr Bas Hofland, a coastal engineer explains.

The new facility cost 26m euros and took two years to build.

It holds 9 million litres of water, pumped in from a reservoir at 1,000 litres a second.

The facility took two years to build and cost 26m euros

The waves are created by a 10m-high steel wall, that pushes the water back and forth.

By making adjustments to this movement, waves can be made to order: from the choppy waters of stormy seas to a single tsunami surge.

They then travel along a narrow 300m-long tank.

At the end, scientists can place full-scale flood-defence technology, such as dams, dykes and barriers, to see if it can cope with whatever nature can throw at it.

"Certain things we cannot make smaller, certain things we want to model at full-scale," explains Dr Hofland.

"Grass on a dyke, or clay, or sands - they are things you cannot scale down because the properties change."

The Netherlands was devastated by the 1953 floods - nearly 2,000 people lost their lives

The Dutch have good reason to be interested in protecting their country from the sea: two-thirds of the land is at risk from flooding.

And they have first-hand experience of the horror that can happen when flood defences fail.

In the winter of 1953, a high tide and treacherous weather combined to create a devastating storm surge in the North Sea.

In the Netherlands, 1,500 sq km of land was flooded, and nearly 2,000 people were killed.

In the UK, too, sea walls were breached, and more than 300 lost their lives. The death toll at sea was more than 200.

It was a turning point: the fight back against flooding became a priority.

The Oosterscheldekering storm surge barrier has been holding back the waves

In the Netherlands, this meant the construction of Delta Works, a network of dams, locks, dykes and barriers to protect the most vulnerable parts of the country.

In Zeeland, in the southwest of the country, Dr Bregje van Wesenbeeck shows me the Oosterscheldekering storm surge barrier.

It's a huge structure, joining two peninsulas. Open for most of the time, its sluice gates can close if sea conditions turn.

The further you plan ahead, the harder it is to predict what is going to happen

Dr Bregje van Wesenbeeck, Deltares

The coastal ecologist says while the Netherlands is better protected than many countries, it still needs to future-proof its systems.

"But the further you plan ahead, the harder it is to predict what is going to happen," she explains.

The UN's International Panel on Climate Change's 2013 report warns that in 2100, global mean sea levels could rise by between 28cm and 98cm.

Another study published by scientists in the Proceedings of the National Academy of Sciences found in the worst case, 600 million people could be flooded annually and this could cost $100 trillion per year globally.

"Your flood risk protection measures need to be adaptive and not very rigid. You don't want to lock yourself in," says Dr Van Wesenbeeck.

"For example, for the storm surge barrier there's a bit of a challenge, because it is kind of rigid, so if there is large sea-level rise we need to adapt it."

She adds that "softer", natural systems, such as sand dunes or the grass-covered dykes, are easier to adjust, and can be built up quickly if required.

The machine can generate any kind of sea conditions to put sea defences to the test

It is these different kinds of systems that will be put to the test in the Delta Flume, which will open in October.

Scientists say that generating ever-bigger waves is the only way to find out if flood defences can cope with increasingly turbulent seas.

Because if their forecasts are correct, our future could be a much wetter one.