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Challenge of Czech floods revealed at joint Scots conference

ICE News

SCOTTISH AND Czech engineers joined forces last month to discuss the infrastructure damage caused by severe flooding in Prague in autumn 2002.

The conference, Flooding 2002, was held in Prague and Edinburgh by the Czech Institution of Structural & Civil Engineers, the Czech Chamber of Certified Engineers & Technicians and the Scottish branch of the Institution of Civil Engineers .

Engineers shared their experiences in assessing structural damage from flooding, implementing flood control measures, and performing remediation work and flood prediction analysis.

In August 2002 over 3km3 of rainwater fell on the Vlatva river basin in Bohemia. Rain fell at 5,200m3 per second, far in excess of the predicted 1 in 100 year flow of 3,700m3 per second.

'This flood was a catastrophe for Prague Metro. The total flood volume was 1.2Mm3 and the damage cost $23.5M, ' said Prague metro engineer Georgij Romancov, presenting a paper on the effect of the flood on the metro.

He said barriers to the metro entrances were used effectively but were only designed for a 1 in 100 year event. This was exceeded during the floods.

In future barriers will be 600mm higher than the highest levels recorded during last year's event.

'Water leaking into the metro was not clean. Many tonnes of waste material was carried by water that had swept the streets of the city centre, ' added Romancov.

Debris and faeces remained in the metro even after the 'filthy stinking' water was pumped out.

Rehabilitation was a gigantic challenge and took engineers seven months to complete.

The first step was to remove the wreckage. Engineers had to work in protective clothing and gas masks while the entire 17km of affected line was cleaned with pressurised water and then disinfected.

Cables and electrical equipment had to be totally replaced with escalators and lifts having to be taken apart to clean and repair them.

Although the tunnel structure was not damaged it still had to be carefully inspected.

Ronnie Falconer from Babtie spoke about a flood defence project closer to home, the $41M Perth flood alleviation scheme.

Its conception was a response to extreme flooding in Perth in the early 1990s causing some $68M of damage.

'The scheme provides protection to the city from direct flooding from the Rivers Tay and Almond and from indirect flooding from local watercourses, ' said Falconer.

Major elements of the project included pumping stations, retaining walls, flood embankments, detention ponds and a massive 84 demountable gates to protect properties and businesses in the harbour area.

'Although the primary function of the scheme was to protect the city from flooding the council has sought to use the scheme as an opportunity to enhance the existing environment, ' said Falconer.

Public consultation was sought at three different stages resulting in the use of natural materials, shallow sloping embankments, the creation of a promenade along the river and minimised disruption to local business.

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