Tidal warriors Birse Coastal on shielding Cleveleys from the rage of Mother Nature

CLEVELEYS IS the archetypal seaside town.

A bingo hall and seafront cafes, matched with an utter sense of physical isolation is enough to begin mourning streets with a Debenhams or a Starbucks.

The presence of more than ten charity shops within a 500mstetch of the high street marks its level of depravity and the initial scarcity of anybody under 60 becomes yet another coastal mark.

While sweeping generalisations are perhaps unfair, a deprived Skegness is not a prosperous Bournemouth, for example, one obvious feature of all coastal towns, and one that poses a greater risk than any of the above, is the sea.

According to the Environment Agency, rising sea levels, coastal erosion and more frequent and severe flooding will put 1m people, and £120bn of infrastructure at risk by 2080.

The great flood
In the town where residents still talk of the “great flood” of the 1970s, where the tide leapt up over the helpless wave wall sea defence, and gushed its way into houses, Cleveleys is in no mood to stand idly by and let it happen again.

Its wide sandy beach and promenade peers out to the Irish Sea to the west, with Morecambe Bay and the Lake District mountains to the north. Wyre Borough Council has sprung into action a mammoth 50-year build programme to defend the town’s 8,700 properties.

Birse Coastal is currently putting the finishing touches to a £22m sea defence structure that stretches more than 1.1km along the coastline.

After arriving onsite in November 2005, after a ten-month Early Contractor Involvement period to finalise the design, Birse is in negotiation with the council over a new section of the works that will extend its time in Cleveleys by 12 months.

It took Birse just over two years to complete phases II and III of the project, essentially a 1.1km sea wall structure that snakes its way in front of a brand new promenade.

Arriving at Cleveleys on a grey and windy afternoon deep into June, the work is an utter transformation and sparkles even when shadowed by dark silvery clouds.

The new promenade is twice as wide as it once was. The promenade’s slalom profile and its intermittent sandy concrete pillars give the impression that you are on the bow of a ship.

That and the whipping winds that send my hard hat hurtling down the promenade is a reminder of just how forceful the elements can be.

First line of defence
The first new line of defence against the sea is a barrier of step-shaped precast concrete revetments.

It contains 3,600 individual precast concrete units cast at SLP precast in Thornton and transported to the scene by road. “It has cut down in traffic substantially,” says Birse Coastal senior engineer Nick Fox. “Otherwise it might have had to have come in from Manchester.”

Behind that is a new middle and rear wall, also made in concrete sections.

Each of the precast concrete revetment units weighs 16 tonnes.

Fox explains that revetments are becoming increasingly more common for coastal defence structures replacing the traditional wave wall, which allowed waves to shoot up and over into the town.

“The revetments kill the wave energy as it goes up the steps, but it also adds amenity because people can access the beach and sit on the steps,” he says. “The steps needed to be extended from the previous level to the existing beach level, which meant that the weight of the fill needed supporting.”

Birse has redesigned and increased the height of the existing walls and it’s now capable of withstanding a one in 200-year storm.

Silent supporters
The ground conditions change within the various sections of the 1.35km stretch of coast. Where the ground conditions are weaker they need some form of strengthening.

Phase III of the new sea wall at Cleveleys, which covers the stretch of the north promenade from Beach Road to Victoria Road West, has been constructed over an old river channel containing deposits of soft peats and clays.

Geotechnical engineers Pennine was drafted in to consider piling options to shore up the ground for the concrete revetment units. Initially thinking it would have to install precast concrete to strengthen the ground, Pennine devised an alternative system for a third of the price.

Vibro stone columns offered a simpler build, as oppose to the complexity of the precast piles and slabs. Governed by the tide, Pennine had just a six-hour window for construction a day.

Vibro stone columns offered Birse cost savings to the tune of nearly £1m. The stone columns were drilled to a depth of 10.5m. The columns work by filling a drilled hole with crushed gravel.

By adding successive charges of stone and compacting each one, a column of very compact stone is built up to ground level. “The stone columns are essentially vertical granular drains that water can escape from accelerating settlement time,” says Pennine design manager, David Preece.

Although slower in settlement time compared to precast concrete piles, there is significant savings in build time as the contractor doesn’t have to factor in the additional slab construction. “We arranged with Birse to monitor the settlement so that it doesn’t put the revetment steps on top until everyone is satisfied that the settlement is complete,” says Preece. After completing the groundworks for phase III in December 2006, Birse was satisfied with the settlement and the revetment steps for phase III is now complete.

Pennine is now carrying out the 250m groundworks for phase IVa. “High tide is around 3pm so generally we’re off a couple of hours before,” says Preece. He explains that all the stone has been sourced from a nearby quarry, Leapers Wood in Carnforth.

In total, 1,080 stone columns were inserted for phase III, and a further 683 for phase IVa. Bespoke access ramps were built to get the Vibro rig onto the beach, which takes around 30 minutes. Fox explains that at times the force of the waves and high tides washed the ramp away. “Fortunately in phase IVa it’s stayed in place,” he says.

Contingency plans also had to be in place in the event plant became stranded on the beach. “In the past we’ve had excavators break down on the beach, says Fox. “We have an engineer on standby who can come out and if he can’t repair it there are ways and means of getting the equipment off the beach. We’ve become masters at it.”

One of the techniques was having spare power packs on hand. In the event of a mechanical failure these could power the hydraulic plant and evacuate the area.

Currently Birse is onsite in Blackpool and Dymchurch installing similar systems to Cleveleys. Its remaining time at Cleveleys depends on it securing the complete package for phase IV which has gone out to tender. It is expected to complete the groundworks by mid-August. “Hopefully we can win the next phase,” says Fox. “There’s at least another 12 months there which basically entails the full revetment and promenade construction.”

Fox has been at Birse Coastal now for more than five years. His work on coastal flood defences has given him a clear perspective of how forceful the sea can be. “I suppose that’s the thing with climate change,” he says, with brazen. “I guess I’ve got a job for life.”