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Floods paralyse Prague metro after doors left open

DELAYS IN closing massive underground steel flood barriers are thought to have led to catastrophic flooding in Prague's Metro system last week.

Two thirds of Prague's Metro system has been paralysed following inundation of 18 or more stations, bringing the Czech capital to a near stand still.

Flooding in the metro coincided with widespread inundation of the city's historic centre leading to 70,000 evacuations, building collapses and widespread infrastructure damage.

Much of the water had subsided as NCE went to press, leaving the city coated in muddy sludge.

It was initially thought that human error was to blame for the catastrophic flooding of the Metro.

Its tunnels are fitted with massive steel barriers, designed by Soviet engineers to withstand nuclear bomb blasts.

These should have been able to hold back pressures many times greater than that exerted by the 30m head of flood water, said Petr Vozarik, technical director of specialist Metro contractor, Metrostav.

Massive lead-lined steel doors are fitted inside the tunnel at either end of each Metro station.

In some of the stations, further blast protection barriers of lighter construction were installed between the ticket hall and platforms.

These were designed to remain standing under a 10m head of water which would exert a force of 10kN/m 2. In the event support frames gave way whenwater reached 10m, suggesting that designs had no margin for error.

Engineers in the Czech Republic have become increasingly concerned about the quality of construction carried out during the last 20 years of Soviet rule which ended in 1989.

But it is widely rumoured that Metro staff did not close the barriers fully, never believing the flood waters would rise so high.

It is thought that operators delayed the decision to shut down the metro for as long as possible to keep the city's population moving as people prepared for the flooding to start.

But the scale of flooding took many officials in the city by surprise. Initial modelling forecast the River Vltava would reach a one in 20 year return height. This was subsequently raised to one in 50 years and then one in 100 years.

In many parts of Prague flood defences were provided with an additional 600mm margin to account for freak events in excess of a one in 100 year return period.

The Vltava overtopped even this, submerging Prague's streets in more than 2m of mud-laden water, and taking everyone, including Metro staff, by surprise.

Across all sectors, the government is having to spend large sums on stabilising or replacing low grade structures, said Mott MacDonald Praha managing director Jiri Petrak.

It is also feared maintenance has been neglected.

Fire crews and Metrostav workers were still pumping out the water-filled Metro tunnels as NCE went to press. It has so far been impossible to carry out inspections of the network.

As the water was sucked from ticket halls and escalator shafts, it became clear that water rushed in with devastating force, stripping away mechanical and electrical equipment in its path.

It is expected that cleaning and repairing damage to the Metro will take months - few expect it to be operational before spring 2003 at the earliest.

Loss of the Metro, on which around 2M journeys are made every weekday, has forced people into their cars, gridlocking the city's already overladen main roads.

INFOPLUS www. nceplus.co.uk/magazine /flooding

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