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Out of the box and into the banks

Piling and foundations

Invisible to most residents of Lewisham, the River Quaggy merits a £20M investment in flood protection by the Environment Agency (EA).

Commenced as an emergency work by the National Rivers Authority in 1998, what is now the River Quaggy Flood Alleviation Scheme is the largest of its kind in the UK, and is in its £6.9M final phase.

Designed by EA framework consultant Halcrow and constructed by framework contractor Breheny, the scheme provides flood protection for the densely populated flood plain of south east London.

Two upstream water storage areas and an extensive programme of river course and bank strengthening measures in Lewisham and Lee Green were introduced, designed to a 1 in 70 flood defence standard.

Sub-contractor awson WAM installed approximately 170m of 'W'-section steel sheet piles that it reclaimed as part of its decommissioning package on the DS1/DS2 cofferdam in Canary Wharf.

Colin Russell, director of Dawson WAM, says: 'The recycling of steel sheet piles can happen in a couple of ways.

Even permanent piles are sometimes removed for some reason and, if in a suitable condition, go into the second hand market to be used in temporary applications.

Those in poor condition are recycled as scrap although this incurs significant energy and carbon footprint penalties.

'What we have been able to do as a result of Halcrow's design initiative and the EA's policy on waste minimisation is quite the reverse.

'We have taken a 16 year old temporary pile that has already fulfilled its design life and, because of its sound engineering properties, combined it with careful extraction and refurbishment, and then installed it permanently.' The sheet piles are finished by concrete infill to the in-pans, and brick cladding with bird nesting boxes and planting areas included in the design.

Dawson WAM used a Giken Silent Piler from a floating support platform to perform the majority of the pile extraction in the cofferdam decommissioning programme. The same rig was used to carry out installation in Lewisham.

The River Quaggy Flood Alleviation Scheme is set to be completed in November 2006.

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