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Invisible mending British Waterways may be the biggest purchaser of English oak in the world, but maintaining the system involves more than high quality joinery. Dave Parker reports from Staffordshire

Britain's canal network, asserts BW Midland & South West regional engineering manager David Bligh, 'is one of the last bastions of the

true civil engineer.'

He goes on: 'We're involved in almost everything, from the maintenance of thousands of historic structures to the design of new bridges - some of them very innovative.

'And we don't just operate in fresh water. At Sharpness Docks on the Gloucester & Sharpness Canal we're responsible for some sizeable marine structures as well.'

Based at BW's Peel's Wharf offices near Tamworth, overlooking the Coventry Canal, Bligh and his 17-strong regional team are responsible for nearly 30 major canals totalling 800km in length, and some 4,000 structures.

'These include 400 locks, 380 road bridges and 18 tunnels,' says Bligh, 'plus weirs, culverts, aqueducts, and nearly 600 accommodation bridges'

There is also the 25ha Rotton Park reservoir in Edgbaston, built by Telford to supply the Birmingham canals with much-needed water which itself is fed by a complex cross-catchment culvert system.

To keep track of this mixed bag, BW recently introduced a system of categorising all waterways structures. Based on a 'linear asset survey', observations every 100m along every canal are logged into handheld computers, identifying any need for more detailed inspections. The system covers all BW's near 20,000 structures and 3,000km of canals.

One reassuring statistic thrown up by the survey, Bligh reports, is that only 220km of 6,000km of canal bank warranted a second look. 'We're always very conscious of embankment safety,' he adds.

Maintaining and restoring historic structures, Bligh says, often involves using the latest and most advanced engineering techniques. 'Our objective is always to make sure that after we've completed our work no-one will be able to tell we've been there. And if we need to use innovative processes to achieve that objective, we will.'

Even such mundane problems as the disposal of material dredged from silted-up canals can have innovative solutions. Although this sludge is specifically exempted from the new Landfill Tax, the new Waste Management Regulations now outlaw the previous practice of 'informal arrangements' with local landowners or the use of BW's own tips.

This could mean paying to have the dredged material disposed of to licensed tips. 'However, we now analyse the sludge and if it is unpolluted and we can show it will bring an agricultural benefit, we can spread it on farmland at a rate of 5,000t/ha,' says Bligh. 'That's about 300mm thick!'

Nationwide, BW has more than 150 craftsmen producing around 100 sets of new timber gates every year for the network's 1,549 locks. But Bligh says any appearance of unthinking conformity with tradition is misleading.

Oak, and other hardwoods, are seen as cheaper and more practical than steel. This does not mean that BW will continue reproducing the traditional designs ad infinitum, he adds. 'We'll soon be wiring up a traditional oak gate with stress gauges and transducers in an effort to improve the basic design, hoping for less operating effort, a better seal, and reduced wear.'

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