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After the deluge

Two years on from the catastrophic Cumbria floods, Jo Stimpson returns to see the climax of the Herculean recovery effort.

It is two years since the catastrophic November day in 2009 that brought unprecedented flooding to Cumbria. Local residents describe how the rain started to fall - as it often does in this part of the world - and then simply refused to stop until it had felled bridges, wrecked roads and cut communities in half.

The swollen rivers Cocker and Derwent invaded homes and businesses, stranded livestock, undermined roads and covered the land with tonnes of gravel. The memories remain fresh, but the damage is not. Some minor footbridges remain out of action, some rural pathways are in need of attention, and heaps of cleared-up gravel dot the landscape, but the towns of Workington, Cockermouth and Keswick are enjoying the results of a recovery programme that is returning their infrastructure to its former health - and in some cases giving it an upgrade.

Big reminder

The Navvies footbridge in Workington is one of the biggest reminders that the floods happened - and rightly so, because it was designed to act as a monument to the disaster that devastated the region and claimed the life of PC Bill Barker. The new Morgan Sindall-designed 96t, 60m single span bridge features sandstone piers and a white steel bowstring arch that is visible from some distance. It was the most recent bridge to reopen, on 10 September, after construction began in spring this year.

“There was a clear demand for at least one of the bridges being a landmark structure,” says Cumbria County Council project manager Geoff Holden. “We wanted to provide a lasting memorial to what happened in the floods.” Public consultation heavily influenced the appearance of the structure, he says.

“There was a clear demand for at least one of the bridges being a landmark structure”

Geoff Holden, Cumbria County Council

The £1.7M replacement bridge over the Derwent in Workington - which carries cyclists as well as pedestrians - benefited from £375,000 of Big Lottery Fund money delivered through low carbon transport charity Sustrans.

Cumbria County Council paid the remaining £1.06M.

Navvies

As an elegant memorial and as a bridge upgrade, Navvies has received plenty of positive reviews.

It is a bridge that draws attention to itself with its bright white colour and modern silhouette. By contrast, other bridge repair schemes have been seamless facelifts that leave their ancient subjects looking as if they had never been damaged.

Workington Bridge - also known as Calva Bridge - looks remarkably untouched, considering that it faced oblivion immediately after the floods, when initial assessments found that scour had rendered it structurally unsound, with demolition the only option left.

Dramatic reprieve

However, once flood waters subsided, making detailed structural inspections possible, Balfour Beatty/Mouchel joint venture Scotland Transerv discovered that the structural damage was not as serious as previously thought, nor had it deteriorated as quickly and seriously as expected. In a dramatic turnaround, the Grade II listed structure was given a reprieve and declared repairable (NCE 15 April).

The three span, 47.5m long masonry bridge sustained serious damage when flood waters washed away roughly one third of the upstream side of one of the two piers that stand in the river. As a result, load was unevenly distributed. The bridge deck dropped by 230mm on the upstream side and 90mm on the downstream side, effectively “twisting” the arch, says Holden. “A lot of head scratching went on as to what could be done with it.”
The discovery that the Highways Agency had strengthened the bridge in a concrete saddling operation in 2003 was crucial to the turnaround in prognosis (NCE 27 May 2010).

“It would have been far easier to walk away from this challenge, knock the bridge down and build a new one”

Tony Markley, Cumbria County Council

“That had stiffened the whole bridge up internally,” says Holden. The bridge reopened to traffic in March this year, following a 16 month recovery operation which was only given a 50% chance of success. Balfour Beatty - working under its Connect Roads highway maintenance PFI contract with Cumbria County Council - jacked up the deck before removing masonry and debris, excavating a cofferdam and then pouring concrete to repair the eroded section of the pier. New piles have also been driven through the stonework to support the repaired bridge from beneath, in another difficult operation, says Holden.

Delicate operation

The delicate operation has returned the bridge to a good-as-new state, with the scars of its trauma unnoticeable to the uninformed eye. The project went on to win the Transport Infrastructure award at NCE’s 3R (Refurb, Rethink, Retrofit) Awards last month - a “feather in the cap” for the reconstruction programme, says Holden. Balfour Beatty was also praised by Cumbria County Council cabinet member for highways Tony Markley for pursuing the difficult repair option when it “would have been far easier to walk away from this challenge, knock the bridge down and build a new one”.

ouse_bridge

Also benefiting from near-invisible repairs is Ouse Bridge, near the majestic Bassenthwaite Lake. This crossing was closed due to scour damage to its piers, but reopened in March 2010 following repairs which have left it looking as handsome as ever. “Protecting British heritage - that’s what it’s about,” says Holden.

“It was a bit of a panic when the bridge collapsed in 2009. All the services people were here at the same time”

Phil Dilworth, Birse Civils

In the case of the 19th century slatestone masonry arch Little Braithwaite Bridge, located near Keswick, heritage concerns have been secondary to more practical issues for the bridge’s main user. The bridge stood on farmer Donald Pattinson’s land, and its destruction cut his farm in two. Pattinson describes a hellish day of rescuing cattle and sheep that had been left stranded and distressed by the rising waters.

“I never want to see it again,” he says. “It was frightening.” The loss of the road bridge, with only a small, surviving footbridge as an alternative, forced Pattinson to send his vehicles on a 6.4km detour whenever they needed to cross the river - making routine farming tasks a hassle.

Emergency grant

The £250,000 project was funded by an emergency grant from the Department for Transport (DfT), and Cumbria County Council’s main highways contractor Amey subcontracted the work to local contractor Stobbarts. Capita Symonds designed the foundations.

The result is a smart imitation of the original bridge, although the new arch was built from precast concrete and clad with slatestone. It is an example of a smaller reconstruction project that goes unseen by most of the local community, but is an important step in restoring the region’s former levels of access.

Still, Pattinson remains nervous about the possibility of a repeat disaster, and says he wishes the river had been dredged to make even more space for the water.

“It’s good to have the opportunity to set the record straight and dispel myths about why the area flooded”

Adrian Bacon, Environment Agency

The focus now is on reinstating the final two of the 20 road bridges that were put out of action in 2009.
Bouthray Bridge in South Lakeland is now under repair thanks to DfT funding. Significant repairs are needed to replace its central pier, which was destroyed by the floods. Work by Amey began in June this year and is due for completion imminently, allowing the bridge to reopen by Christmas.

northside_road_bridge

The second of the two bridges is a much bigger job. The original 1903/1904-built Northside Bridge was destroyed by the raging floods, and it collapsed into the River Derwent

Although a temporary Jansen-manufactured, Morgan Est-built road bridge nearby gives traffic a route across the river, the completion of Northside will provide a permanent crossing and will signify the end of a difficult chapter forWorkington, which suffered the region’s highest levels of bridge damage.

Principal contractor Birse Civils and piling subcontractor Balfour Beatty Ground Engineering (BBGE) began work on site on 15 August.

Three span structure

The new bridge is to be a three span structure with a total length of 152m - a design that differs from the original plan to build a two span asymmetric bridge similar to the original.
Architect Ron Yee worked with consultant Capita Symonds to devise the structure’s final appearance.

“We had a lot of options,” says Capita Symonds project manager Mike Briggs. “[Yee] advised us from an architectural point of view what would look best. He thought a three span balanced cantilever looked more pleasing.” To achieve this symmetry, around 40m of ground must be excavated from the embankment on the south side. Capita Symonds also dealt with design complexity due to the bridge’s slight curve.

On site, work has slipped a month behind schedule because of geotechnical problems. Roughly three weeks of trial hole work was needed to survey all the site’s utilities and services, which were not positioned quite as expected due to emergency diversion work carried out in 2009.

Collapse panic

“It was a bit of a panic when the bridge collapsed [in 2009],” says Birse Civils site agent Phil Dilworth. “All the services people were here at the same time.”

Surprises also came from the site’s ground conditions, which Briggs says “haven’t quite been what we expected”. Ground investigations established that the ground was boulder clay, and the data indicated that piling activities would be structurally sound.

But when piling commenced it became apparent that the ground contained more sand and silt than anticipated, and excavations were collapsing at depths of around 18m before piles could be cast, so a change of tactic was needed. Steel casing was settled upon as an alternative method - but friction prevented it from being inserted, says Briggs. Finally, the team opted for using a polymer fluid to support the borehole as it was drilled.

“It takes quite a lot longer than the original method,” says Briggs. Thankfully, these problems only occurred on the north side of the site, and groundworks by BBGE on the south side proceeded according to plan. A total of 72 piles were constructed to a maximum depth of 25m.

Now, pier construction has commenced with the concrete pour for the pier bases. The sandstone piers will have a curved profile and a tapered shape, to minimise the chance of scour.

They - like the abutments and approach walls - will be clad as far as possible with stone recovered from the original bridge.

“There’s a strong public desire to use as much of that as possible,” says Briggs.

“People felt they wanted to see the stone reused. But there’s not enough to do the whole bridge.” Supplementary sandstone in the distinctive red colour of the local area will be brought in from a local quarry.

Weekend possesion

The first steel beams are scheduled to be placed during a weekend posession in late January, with that work continuing into February.

The 700mm wide beams have a curved profile which makes them 3m deep at the piers and 1.3m deep at mid-span. A 1,000t crane is needed to lift the largest beams. The concrete deck will then be constructed from 20 March, ahead of a 2 July opening date for road traffic. Both sides of the bridge are being worked on concurrently.

The new structure will be much more hardy than the old one. The piles will enable the bridge to remain standing even if it should sustain severe scour damage, and the bridge is designed to withstand a 1 in 1,000 year flood event.

One of the Northside Bridge project’s biggest challenges, says Dilworth, is the cramped site, which at just 300m long is unusually small for a structure of this size. “We haven’t got much room,” he says.

Two other towns where space is tight are Cockermouth and Keswick, where homes sit directly above the rivers which overwhelmed flood walls in 2009.

That year, £1.6M was spent on emergency repairs to third party walls in Cockermouth. These are walls acting as flood walls but not officially designated as such. Some of them failed in the floods. That work restored the town’s previous level of flood defence.

Increased flood defence

Now, the Environment Agency is working toward delivering two projects that will deliver an increased level of flood defence.

In Keswick, work has been underway since February this year on a £6.1M scheme to improve protection to 180 properties from the River Greta. Contractor VolkerStevin will complete the works in July 2012.

Existing walls are being strengthened, other existing walls are having their heights raised, and new reinforced concrete flood walls are also being built.

The project has been sensitve to residents’ concerns, and as such some of the new walls will feature glass panels to maintain views of the river.

A major challenge is public perception of whether flood walls are the best solution, says Environment Agency flood and coastal risk management engineer Adrian Bacon. “A lot of people have ideas about what we should be doing,” he says.

“We did the whole optioning process. It’s good to have the opportunity to set the record straight and dispel myths about why [the area] flooded.”

Meanwhile, the Cockermouth Flood Action Group is waiting to hear confirmation in February of whether a similar project in its town will receive funding from the Environment Agency. The £4.4M Cockermouth scheme would reduce flood risk to 360 homes and 55 businesses and would involve raising flood walls and embankments on the rivers Cocker and Derwent. If funding is secured, the Environment Agency says it hopes to have planning permissions in place by April 2012 with construction starting soon after.

Continued response

So although next summer will bring the completion of the Northside Bridge and the Keswick flood defence scheme, Cumbria’s engineering response to what happened in 2009 will actively continue - and will likely be talked about for as long as the unprecedented floods remain in living memory.

Holden says the second anniversary of the disaster marks the fact that the recovery is now in its “final stages”.

“It’s been a lot of work,” he says. “It has been rewarding at times, and it has been frustrating at times.”

Although the initial emergency situation meant the Barker Crossing temporary footbridge and the Workington temporary road bridge could be constructed very quickly, subsequent projects have been subject to normal planning processes, which explains why the programme is only now drawing to a close.

If all goes to plan, he says, there won’t be a third year of reconstruction. Cumbria will be back to its old self - or perhaps a slightly improved version.

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