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Coping with catastrophe

Flooding & coastal management - Bewdley: Towns and villages along the Severn were devastated by the floods of winter 2000. Diarmaid Fleming went to see how one village is fighting back.

The beautiful village of Bewdley lies deep in the Worcestershire countryside beside the River Severn. Just over a year ago, much of it lay under the river, deep beneath flood water levels unseen for 53 years. The floods were a catastrophe for the town, with around 170 properties inundated in November and December 2000. River levels reached an astonishing 5.6m above normal summer levels, destroying houses, shops and businesses.

Bewdley was not alone:

across Britain communities were devastated in a deluge which appeared to arrive without warning after some of the wettest weather on record.

Lewes railway station looked like a canal, the centre of York was centimetres from inundation, while the residents of Yalding in Kent watched in terror as the River Medway rose to record levels.

The floods evoked a sense of desperation and helplessness in affected communities, heightened by a belief among some that they were an inevitable consequence of global climate change. Attempts to stem the floods may have seemed to those remote from their reach a Canute-like endeavour, but for those affected, failure to find a solution could mean the loss of home and community.

A year on, better weather appears to have offered some respite, without a repeat of 2000's record rainfall. Walking along the scenic banks of the Severn at Bewdley today, it is difficult to imagine that most of the pretty houses, shops and cafes were submerged just over a year ago. Only occasional faint stains mark the height reached by the surging flows.

But the painful memories of last year have not been forgotten by those affected and work has begun on the installation of a German-developed system of demountable barriers - the first in the UK - to prevent a repeat.

The town is lucky. 'Bewdley and Shrewsbury are the only two schemes in the country to get full approval since the floods of last year, which is a great achievement, ' says Environment Agency Upper Severn defence and water resources manager Peter May.

The early start enabled by a £5M government grant was helped by a strategic study of the River Severn already under way which provided essential engineering and hydrological information. Government and Agency policy now dictates that all schemes have to adopt a 'holistic' catchment-based approach.

Diving in to sort out a local problem cannot be done - instead, detailed studies of effects throughout a catchment and on other communities must be examined before a decision can be made on how to proceed.

A snapshot of Bewdley's experience gives some idea of the complexities and time involved in providing flood defences.

Despite the grant, Treasury funding rules mean that the town's east bank - which has fewer buildings at risk - will receive no protection and will inevitably flood should the waters rise again. All schemes are subjected to a cost benefit analysis, and failure to meet the Treasury's criteria means no protection, regardless of how high the waters could rise.

The result could be neighbours on one bank peering from behind defences at their neighbours' flooded homes across the river. 'Unless you get changes to flooding rules, you are likely to have the same situation elsewhere as you get here, ' says EA Midlands region engineering services manager Roger Prestwood.

But schemes also need community support. A high profile consultation and information drive at Bewdley followed soon after the floods abated, with considerable local participation.

And with the longest river in Britain the cause of the problem, not surprisingly, many wondered if measures taken elsewhere could alleviate the problems flowing into Bewdley.

'There were many options suggested, but we had to explain the engineering reasons why these would not be possible, ' says May.

'People thought that measures at the Llyn Clywedog reservoir and Lake Vyrnwy could help Bewdley, ' says May.

But the reservoir is so far upstream that its catchment represents only 1% of the total. Any benefit to Bewdley from changes such as increased storage here would be negligible, ' he adds.

Similarly, the lake would have little influence. And increasing the capacity of the flood plain upstream would require higher embankments for 40km and would merely transfer the problem elsewhere. A dam would cause similar problems.

Dredging to allow for the ninefold increase in flow of 675m 3/sec during a one in 100 year event would have meant blasting the rocky riverbed to increase its depth by 3m. Aside from untold damage to the river habitat, major structural work to bridge and river structure foundations would have been needed.

Bypass channels big enough to accommodate such peak flows would have been impossible to construct because it would mean massive excavation and destruction of property in the town. And no fewer than six 7.6m diameter tunnels - each around the size of the Channel Tunnel - would have been needed, at a cost of around £460M. Storage underground was similarly ruled out on cost.

'Flood defences in the town were the only option, but naturally in a town like this where the river is central and provides beautiful views, people were concerned about what affect they would have, ' says Prestwood. So for the first time, the EA decided to adopt a system of demountable defences, previously used successfully in Germany.

The IBS system provided by Bauer Foundations consists of 2.8m high aluminium posts at 3m centres, which support a series of horizontal aluminium 'dam beams' which are installed singly to give different barrier heights. Rubber seals between the posts and beams prevent leakage.

'All the barrier parts will be stored in pallets away from site.

Once the flood warning system alerts us that the barrier is needed, trained staff will bring the barrier to site and erect it, ' says May. Complete erection will be achieved in as little as five hours.

Apart from slots for the posts, there will be no evidence of the barriers when they are not in use. A small section not affecting the views will be permanent. But underground, considerable changes will take place: a £1.9M contract awarded to Birse involves installing raking piles and associated works to support the defences, while contiguous piles into rock will form an underground barrier to prevent water flowing through the highly porous made ground and alluvium. Design work is by consultant Halcrow.

But preventing flow from the river equally prevents flow from the ground on the other side. Rising groundwater could then cause flooding too.

'When you get a really high river and a big storm with high rainfall, the river can flood the sewers. You could put in a flap valve to stop the river coming in, but then you just get flooding from the sewers, ' says Prestwood.

To prevent this, Severn Trent Water has also agreed to install a new pumping facility which will enable pumping of stormwater over the temporary defences and into the river. Groundwater levels, however, have to be carefully monitored: major changes could affect the old foundations of the buildings the flooding is designed to protect.

This first phase at Bewdley extends 180m north or upstream of Telford's historic bridge in the town, with completion by the summer. A second phase covering 400m to the south will follow next year.

Fighting the floods elsewhere

While Bewdley has already started work on new barriers, at the other flashpoints of 2000, the battle is taking a different shape. York, Yalding in Kent, Lewes and Uckfield saw some of the worst flooding and at each area detailed catchment studies are under way.

Engineers responsible for each area say that decisions on new defences will not be taken until these studies are completed, but interim local measures such as improving existing defences have been carried out.

'The water came within 5075mm below the top of our defences at York, while other undefended areas were flooded.

Since then we've plugged the gaps in defences and refurbished a pumping station which we had lots of problems with before. While the weather has been kind to us, were it to worsen we would be in a better position than we were last year, ' says EA Yorkshire Dales areas flood defence manager Peter Holmes.

A hydrological study of the River Ouse catchment by consultant Binnie Black and Veatch is due to for completion in April, making it too early to say what new defence works might be built or when.

Proposals for Yalding in Kent are at a similar stage, with defences relying on the outcome of both a River Medway strategy study, and a catchment management plan - one of five such pilot projects around the country. Local repairs have been carried out, but major works will have to wait.

'We have carried out works in isolation where we can, but we want holistic rather than site by site solutions. In Kent, the catchments are relatively small, so there is a greater danger of effects being transferred to downstream communities than in larger catchments. So we must identify solutions on a catchment basis, ' says EA Kent area flood defence manager Andrew Pearce.

This could take at least year he says, adding that the severe rainfall and high groundwater which caused the flooding did not now apply, but that the risk still existed as conditions could change.

In neighbouring Sussex where Uckfield and Lewes were badly hit, groundwater levels in the South Downs are 30m lower than a year ago, says EA Sussex area flood defence manager Rupert Clubb.

Local repairs have been carried out, but again, larger scale studies under way will determine the scope of long term works, with any initial start unlikely until 2003.

In the meantime, the risks of flooding are no different to what they were in October 2000. 'The public's expectation of local authorities and the EA is very high - they want to see things happening and work being done.

'But some of these schemes, especially in tidal areas, could take six or seven years and are not easy. We have to get it right and not adopt some kneejerk solution which would cause problems elsewhere, ' says Clubb. Keeping the water back is not the only problem: despite the horrendous flooding suffered by Sussex, its councillors on the local flood defence committee refused to approve the budget requested by the EA, leaving it £0.5M short.

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