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Stuart & Devon's point: we must act on flood defences

Many old anchored structures along rivers and estuaries throughout the UK are failures waiting to happen, say Stuart Littlejohn and Devon Mothersille.

Experts are generally united in their view that the effects of climate change threaten world security to such an extent that billions of people will be at risk from storms and floods in the years ahead.

Water levels reached 150-year highs during August 2002 with associated flooding across central and eastern Europe. As a consequence winter storms are now judged by the insurance industry to represent the largest potential event loss in Europe.

The Association of British Insurers has identified in London alone, 500,000 houses, 200 schools, 16 hospitals and eight power stations located on flood plains. Under these circumstances riverside containment structures, in particular anchored quay walls, represent a first line of defence and are key elements of the UK's infrastructure. Such structures exist throughout the country and can be seen from Inverness and Fraserburgh in the north to Portsmouth and Southampton in the south.

Downstream of the Thames Barrier, 7km of raised river walls are tied back by well over 1000 anchorages to provide lateral restraint and resistance to overturning. These anchorages were designed and installed in the 1970s, often with corrosion protection considered inferior or inadequate by today's standards.

All these anchorages are exposed to an aggressive environment and while the walls have been designed conservatively (such that isolated failures can be accommodated), when two or three neighbouring anchorages fail, a progressive mechanism can develop (akin to unzipping) resulting in collapse. Such a failure occurred on the River Thames in 1990 after a service life of 21 years because of corrosion and overloading.

Efforts over the past two years to persuade the Environment Agency to inspect the physical condition and load-holding ability of at least a sample of river wall anchorages, have been unsuccessful. Without this knowledge of the anchorages, for example, under the stressing head not visible externally but known to be most vulnerable to corrosion, it is impossible to carry out a risk assessment. Therefore, it is difficult to understand how the Agency can even start to determine what priority should be given to this type of work.

To avoid doubt, inspections are required now, otherwise in the event of a collapse and flooding of property – including potential loss of life – there will be accusations that no one in authority was advised of the problem or, worse, could not be bothered to implement a routine inspection programme.

The issue was raised in the keynote address and in several presentations delivered at the International Conference on Ground Anchorages and Anchored Structures in Service 2007, held at the Institution of Civil Engineers in late November.

These presentations illustrated the type of deterioration known to exist on anchorages exposed to aggressive environments along river walls. It was clear during ensuing discussions that many engineers share common concerns about sustainability of old anchored infrastructure. The worry is that unless decision makers within government departments embrace the issues and take responsibility then many old anchored structures along rivers and estuaries throughout the UK are failures waiting to happen.

There must be funding to support programmes of inspection, testing and maintenance. In cases where inspections highlight unacceptable tendon exposure to corrosion, or monitoring confirms tendon overstressing, results can provide an early warning of the need to carry out precautionary or remedial measures, to safeguard integrity and performance of the anchored structure.

Despite the benefits, insufficient attention is paid to routine maintenance inspections and service behaviour monitoring, but the potential consequences should not be ignored.

Awareness of the issues is a starting point but without affirmative action to commission suitable programmes, there is a danger the legacy of reliable anchored structures will be lost for future generations.

Stuart Littlejohn is a professor at the University of Bradford and Devon Mothersille is director at Geoserve Global.

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