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Defending The Front

Tide and time may wait for no man, but Galliford Try is tackling both with the construction of new coastal flood defences in north Wales. Claire Symes visited the site to find out more.

The beach has always been the top spot for tourists in the Welsh seaside town of Rhyl.

But this year the beach had a new attraction - a live piling and construction display complete with its own bouncer.

But the machines were not there for entertainment - they are being used by main contractor Galliford Try to build new flood defences for the western side of the town.

The project is designed to reduce the flood risk in west Rhyl and protect more than 2,000 residential and 500 commercial properties against a 1:200 year storm event.

“The existing defences are also 100 years old and are starting to deteriorate,” explains section manager Bob Humphreys of Denbighshire County Council, the client for the scheme. “The concrete walls are cracked and are not high enough.”

Humphreys adds: “There have been some flooding problems in the past and although there haven’t been any significant events, this stretch is at the highest risk on this coastline.

In the 1990s there was a severe flooding event at Towyn along the coast and many people locally remember the impact.”

European funding

The majority of the funds for the £10.6M project have come from the Welsh Government and European Convergence Funds, with the remainder coming from Denbighshire County Council.

“The Welsh Government wanted some schemes that could be progressed quickly to access the European funding and we were fortunate that the need for improved flood defences in west Rhyl was identified in 2007 as a result of a planning application for a site behind the esplanade,” says Humphreys.

Galliford Try’s compound is actually sat on the site behind the seafront that stimulated the whole scheme into action - before the proposed residential and commercial development for the site could gain planning consent, the flood risk needed to be reduced.

Martin Wrights Associates undertook the initial study and then went on to win the European tender for the work in 2009.

“The contract was to take the project proposal forward to feasibility, design and then put it out to tender,” says Martin Wright Associates project manager Bill Fishwick.

Galliford Try won the £7.6M contract to build the scheme in January 2011 and work on site started in May.

“Until this problem is resolved there is a gap in the project and the overtopping risk will still exist”

Phases one and two are being carried out concurrently with phase one involving reconstruction of the training wall that guides the flow of the River Clwyd, while phase two takes the defence work from the landward end of the training wall and up river and into the harbour area.

Phase three of the scheme was to involve reconstruction of the esplanade eastwards from the training wall towards the Rhyl tower.

But this has run into difficulties as the Welsh Government says the promenade and stepped revetment creates an amenity rather than just a flood defence and hence does not qualify for funding.

Humphreys says negotiations are ongoing to find a design solution that meets the funding criteria and he hopes that one can be found before Galliford Try completes phases one and two.

“£3M of the project funds have yet to be approved,” he says. “We are currently looking at beach recharge as a possible solution.

“Until this problem is resolved there is a gap in the project and the overtopping risk will still exist.”

Construction work

“The existing training wall was built to guide the river out to sea and prevent erosion of the beach to the east,” says Galliford Try site manager Christian Chambers.

“The existing structure is formed by steel piles with a timber capping beam but has been damaged and was estimated to only have five years left.”

Although the structure is damaged, removal of the wall would have left Rhyl vulnerable so Galliford Try is refurbishing the existing wall and building the new wall over the top.

In total, 60,000t of rock armour, ranging in size from 1.5t to 9t blocks sourced from local quarries, is being used on the project.

“We looked at importing the rock but it would have worked out more expensive and the carbon footprint was also larger,” explains Mike Wellington associate director of fluvial design at Martin Wright Associates.

Inner_harbour_wall

Tests on local rock proved that it would meet the requirements and is being delivered to the project by road.

Once on site, the rock is given an initial sort and visually inspected to separate it into different weight blocks and is then transported onto the upper beach ready for the tide to go out.

Galliford Try is using a Caterpillar 385 excavator and a fleet of Volvo A35 dump trucks to handle the rock.

“We have a four-hour window when working on the furthest point of the training wall and between five and a half and six hours at the landward end,” says Chambers. “We are working through the night to make the most of the tide but rock sorting is only carried out during the day.

Noise can be an issue on this project and we have changed our working pattern to minimise the problem.”

Galliford Try is building up the training wall by placing a geotextile over the existing wall between newly installed sheet piled walls and building an anti-scour defence on the riverward side.

“We have a four-hour window when working on the furthest point of the training wall and between five and a half and six hours at the landward end”

The rock armour is then placed between the sheet pile walls over the geotextile.

The new structure is designed to be 250mm higher than the old one to take account of the rise in sea level, but it has also been designed to allow it to be raised again in the future if the further predicted sea level rises happen.

“The new training wall has a flat 3.6m wide crest that will enable the wall to be raised in 1m increments,” says Wellington. “Anything less than a metre would just end up redistributed along the foreshore but building the wall higher to cope with future sea level rises would have had an adverse impact on the flow of the river.”

Chambers says work is progressing well, but the construction of the old training wall was different from the expected concrete structure. “The wall actually turned out to be a sheet pile wall with a timber capping beam,” he says.

The aim is to get 85% of the training wall completed by Christmas.

“The weather has not been a problem so far but we are coming into the period when storms can be expected but now we are closer to shore, the work should be impacted less by weather,” says Chambers.

Although phase two is sheltered, it is not without its challenges.

The main one is the wreck of the City of Ottowa - a boat brought into the harbour in the early 1900s to be broken up at a shipyard once located here.

The vessel sank before work could begin.

Other issues in this area include the grade II listed Foryd Road bridge, the need to create space for a new cycle bridge which is due to be built next year and allowing boats moored in the harbour to continue using facilities.

“There is not much left of the City of Ottowa - it is only visible at low water - but there is enough of it to get in the way,” says Chambers. “The work on the inner and outer harbour is being carried out from the shore to avoid damaging the wreck and obstructing the harbour.”

Mass infill

The 470m long outer harbour defences are formed by mass infill with rock armour over geotextile between the existing harbour sloping sea defences and a new sheet piled wall.

Although sheltered, piling contractor Ivor King of Nuneaton could only drive the piles during low tide and the hammer was specially selected to minimise noise.

1954

The 3.5m and 8m long piles have been alternately driven in pairs to 3m depth to create a crenulated wall that is designed to dissipate wave energy.

“This section is designed to address the overtopping and breaching issues,” says Wellington.

The sheet piled wall continues into the inner harbour but as a continuous structure formed from 6.5m long sheet piles driven 5m in front of the existing wall.

Around 3,000m3 of concrete will be used to infill behind the new wall.

The 220m long inner harbour wall will be completed with the placing of a precast concrete recurve wall on the top which has been designed to avoid the need for a capping beam.

Once the precast wave wall is installed, Galliford Try will then build up the cycleway behind so that cyclists and walkers will still be able to enjoy the view.

With such a long construction period, local people have been very interested in the scheme but the overall response has been mixed despite the potential benefits.

“There has been more concern about the actual construction than the outcome of the work,” says Chambers.

The project team has invested considerable time in visiting local schools and groups to explain the risk of flooding and need for the scheme.

“There have been some flooding problems in the past and although there haven’t been any significant events, this stretch is at the highest risk on this coastline”

Martin Wright Associates also developed a computer-based fly through of the project to help people visualise the finished scheme.

Traffic management has also been an issue for the project - Galliford Try has been allowed to close part of the seafront but during the summer a lot of tourist traffic comes into the town from the west, so the company tried to remove the traffic lights whenever possible.

But the impact of the work extends beyond the seafront and onto the beach and in the harbour too, and this has brought other challenges for the site team.

The project itself became an unlikely tourist attraction in the summer season with many visiting the visitors’ centre on site to understand what was going on.

“We were keen not to make the beach look too much like a construction site so rather than fencing off the area where we were working, we employed security guards to keep people away,” says Chambers.

Extensive consultation was also carried out with the harbour users and some of the work was delayed to avoid impacting on tourists.

Galliford Try also provided an escort through the work to the landing point on the existing training wall.

With the tourist season over for 2011, Galliford Try’s biggest challenge is now the winter weather but the company is on course to complete phases one and two in spring 2012.

Denbighshire County Council’s Humphreys is optimistic that the funding issues for phase three will be resolved by then, so the whole scheme can complete on schedule in 2013.

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