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Limestone barrier protects sea town
A tourist town in mid-Wales is in the throes of a
huge coastal protection scheme after winning funds from the
Welsh Assembly Government.
Aberaeron is a pretty Edwardian coastal harbour town on the
west
coast of mid-Wales. Sandwiched between the better known resorts
of New Quay to the south and Aberystwyth a few miles north,
it has basked in its unpretentious ness for more than 100
years.
Brightly coloured houses cluster around its harbour and quayside
in a vista that only those tourists in the know have wit nessed
over those years. But unless a bid by local authority Ceredigion
County Council to stem the destructive affects the Irish Sea
is having on its coastal protection structures succeeds, there
may not be that much town left for tourists to visit.
Aberaeron is fortunate that it lies on the west coast of Wales.
Coastal protection projects on the east coast of England have
been few in recent years.
In mid-Wales it is a little different. There is a pot of
funding cash from the Welsh Assembly Government waiting to
be spent on these types of schemes. Richard Edwards, head
of the Highways, Property and Works department at Ceredigion
County Council, is aware that his project is fortunate to
have won the coastal protection postcode lottery.
"This is a Welsh Assembly Government-funded scheme,
not Department for Environment Food and Rural Affairs,"
he says. "Within Ceredigion there is a need for about
£40 million to be invested in coastal protection works."
Limestone protection
Contractor BAM Nuttall has taken a £4.5 million deal
with Ceredigion County Council to deliver Aberaeron's North
Beach protection scheme, which will see 79,000 tonnes of locally
sourced carboniferous limestone used to protect the town.
Existing wave walls will be heightened and refurbished while
the beach is reprofiled and nine new greenheart timber groynes
will be built out seaward from the land. In addition, site
workers will build two rock groynes using the same huge 6
tonne chunks of rock that will also form a 500 m-long continuous
revetment along the north side of the harbour mouth and on
beyond the terraced cottages of the north part of the town.
A further steel sheet pile flood wall is also being built
as part of the project.
"It is a very significant scheme for Aberaeron,"
says Mr Edwards, "There have been times when the sea
wall has threatened to breach, although it never has. There
has been significant overtopping during storms and high tides
and the existing groynes have deterio rated very badly. We
seemed to be regularly spending £100,000 on patching
and repairs to the exist ing sea wall so there was obviously
a need for this scheme."
Which is where Ray Jones, BAM Nuttall site manager for the
North Beach project and his team of experienced staff who
will help deliver it come in. It is halfway through a 42-week
delivery pro gramme for the coastal protection scheme and
the local rugby club has also played its part.
Initial tenders for the scheme were based on the rocks for
the revetment being delivered by sea. Unfortunately, this
put the project approximately £2 million over budget
and so the only option the client could consider was one where
the boulders are delivered overland. A staggering 4,000 lorry
movements will transfer the 6 tonne average-sized rocks from
quarries around Minffordd on the edge of the Snowdonia National
Park some 64 km to the north.
A temporary haul road was built through land owned by the
local rugby club to serve the site and redirect the 20 tonne
pay-load wagons from Aberaeron. "We were able to negotiate
an alternative access along the south of the rugby pitch and
down to the beach. In the end, it probably saved the scheme,"
says Mr Jones.
Construction of the 250m-long haul road began in December
2008 using a 600 mm-thick compacted layer of capping material
and, since the first week in January, hundreds of lorries
have used it. Each day 8-900 tonnes of stone have been delivered
to the site and the lorries have also helped to build up a
stockpile of the 79,000 tonnes of carboniferous limestone
that will be used during the con struction of the rock revetments.
Rock armoury
These rocks are unloaded from the road wagons and placed in
the stockpile using a 45-tonne grab. This also loads the dump
trucks, which take the rocks out to the dozers and the 35-tonne
grab-fit ted excavators, which place the 6 tonne rock armour.
Existing beach cobbles and pebbles are dug away to the required
profile and the material stockpiled. This excavated sec tion
is then covered top to bottom by a 6 m-wide strip of geotextile
and the rock armour placed on top in two layers total ling
2.2 m-thick at a gradient of 1 in 2.5. This is critical to
the proc-ess and the grab handler's skill is key if the huge
chunks of stone are placed in the ideal three points of contact
between each rock, which ensures that some of the wave's energy
is absorbed by the revetment.
The stored beach material is then used to reprofile the beach
at a gradient of 1 in 6.This beach will be protected by both
the rock groynes, and the timber groynes, which are built
using steel-tipped greenheart timber piles and whaler boards
supplied from East Africa.
More than 160 of these 305 mm square section timber piles
are to be driven between 4 and 8 m at 2.5 m centres into the
beach using a 5 tonne drop hammer piling rig. The 225 x 150
mm whalers are butted and fixed to the northern side of each
of the scheme's nine timber groynes, which stretch out some
30 to 40 m into Cardigan Bay.
The 277 m long MX16 profiled steel sheet piled wall flood
defence at the northern end of the project is driven 1 to
4 m into the underly ing glacial till using a vibrating hammer.
It is being shot blasted and spray-painted 'leaf green' and
will be capped at the same 6 m above ordnance datum as the
other structures in the scheme.
By the end of September the town will be protected from all
but the freakiest of tidal events.
Cost
Effective, Coast Protective
In Aberaeron a major event would
mean the flooding of most of the business district and
many of the homes that lie between the A487 road that
slices through the town and the sea front, but the cost
effective ness of protecting these properties is not
the only consideration.
On most schemes funded through
the Department for Environment, Food and Rural Affairs,
measures are set down to assess the viability of protection
schemes. These cover topics including the number of
properties that will benefit by being moved out of at-risk
areas and the number of low-income households that will
be moved out of at-risk areas thanks to the scheme.
There is also the effects the scheme will have on biodiversity.
"There hadn't been any major events here, but in
terms of a tidal risk then it is entirely justified,"
says Mr Edwards.
"High water levels are predicted
to rise around the world and flood defences around the
town, which has just celebrated it bi-centenary, had
deteriorated badly."
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Article courtesy of Construction news - 07/05/09
Further Info
Peter Bishop - Head of Public Relations & Corporate Communication
BAM Nuttall Limited
St James House, Knoll Road, Camberley,
Surrey GU15 3XW
Tel: 01276 63484
Fax:01276 66060
peter.bishop@bamnuttall.co.uk
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