independent

Sunday 20 April 2014

Tried & tested: how other countries have built effective flood defences

Left: Flood defences in the  Netherlands Right: A massive water discharge tunnel on the outskirts of Tokyo
Left: Flood defences in the Netherlands Right: A massive water discharge tunnel on the outskirts of Tokyo

Ireland will need to follow the examples of these countries if it is to build effective flood defences

NETHERLANDS

SOME of the best flood defences in the world are to be found in the low-lying coastal country of the Netherlands.

The measures taken to bulk up their protection followed the catastrophic loss of more than 1,800 lives in the North Seas floods of 1953.

Work is continuous to improve its network of locks, sluices and barriers – with efforts to make the defences bigger and river-widening projects undertaken thanks to new technology.

A mix of natural dunes, dikes, dams and storm surge barriers protect its coast.

Around 67pc of the population live within dike rings, or embanked areas, which are a series of polders surrounded by a flood defence dike. It is estimated 0.1pc of the entire gross domestic product of the country – more than €500m – is spent on its network of flood defences.

RHINE DELTA

A centuries-old policy involved raising the crest levels of the dikes to protect from flooding.

However, in 2000, this was abandoned in favour of 'Room for the River'.

This has involved widening cross-sections by placing the dikes further away, enlarging the river channel and by lowering the lands close to the river to reduce flood levels.

BELGIUM

Moves were made to opt for the cheaper and more environmentally friendly method of natural floodplains over dams in Belgium. It proved successful and it was estimated to be cheaper than building a large dam near the city.

JAPAN

A mammoth feat of engineering protects the Japanese city of Tokyo from floodwaters and the incessant rains brought on during typhoon season.

On the outskirts of the city, it has a massive water discharge tunnel (above) built at a cost of €2.2bn.

This involves a series of five massive sinkholes, or water tanks, designed to catch the run-off from the flooded rivers. The holes measure in at up to 74m high and 32m wide. The concrete tunnel transports the water through a tunnel that lies 50m underneath the river basin, and pours into a massive reservoir. Turbines then funnel the water out through sluice gates into the nearby Edo river.

NEW ORLEANS

In the aftermath of the devastating Hurricane Katrina, at an estimated cost of €10.7bn, a network of levees, floodwalls and pumps was erected to stop the low-lying parts of the city being swamped.

Irish Independent

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