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Marine: Colwyn Bay recharge

The popular seaside town of Colwyn Bay is getting a boost from a £6.8M scheme that will recharge the beach and provide valuable flood defences.

Shoreline: The pipes are moved into position

The pipes are moved into position

A hundred years ago, Colwyn Bay in North Wales was a thriving coastal resort. Its sweeping promenade gave access to miles of beaches that had offered fresh air and good times for Victorians and Edwardians of all ages and incomes.

But the second half of the 20th century brought increasingly affordable air travel, broadened horizons and higher expectations from the public.

Tourism declined, local investment dwindled and the glory of Colwyn Bay began to crumble. At the same time, the town’s coastal defences deteriorated and left the area vulnerable to the forces of nature.

The grading analysis of the sand we use is very important - it can’t be too coarse or too fine

In 2008 the town was designated as a Strategic Regeneration Area by the Welsh Government, and an infrastructure investment drive to protect coastal communities - combining national grant funding streams with European money - led to local authority Conwy Council establishing the Colwyn Bay Waterfront Project. Now the area is alive with activity to deliver new coastal defences that will protect and regenerate the town over the next 100 years.

At the heart of this initiative is a £6.8M scheme to recharge the beach - a project that will, by the middle of the summer, have raised the level of the beach by up to 3m. This extra height will provide the first line of defence against flooding and storm damage, explains Conwy County Borough Council interim head of technical services Hywel Jones.

“It keeps the sea away from the sea wall,” he says. “Because of this increased height, storms hit that vulnerable sea wall and promenade with less ferocity.”

Wave reduction

The new raised beach will reduce the size of waves, while a new revetment will reduce their impact on the sea wall and promenade.

Different solutions were needed for different parts of the bay, Jones adds, with the western half better suited to sand because of the tidal conditions, while the eastern part will need rock.

“There was the possibility of using a rock revetment all the way along, which would give a very hard defence, but it would still be low level and provide little access,” Jones explains. Using sand in combination with control structures creates an infinitely more pleasant beach for the public than rock.

There was the possibility of using a rock revetment all the way along, but it would still be low level and provide little access

The 3m rise in beach level is being achieved by bringing in a total of around 220,000m3 of sand dredged from the Irish Sea. But it’s not just any old sand, as Dave West, contracts manager for the scheme’s contractor Galliford Try, explains: “The grading analysis of the sand we use is very important - it can’t be too coarse or too fine. Too fine and it would be washed away too quickly; too coarse and it wouldn’t be pleasant to walk on or play in.”

Belgian dredging contractor Jan de Nul is responsible, under licence from the Crown, for harvesting the sand.

The firm is using a trailing suction hopper dredger to suck up sand from a pre-designated area of the seabed about 16km out, which is then stored on board in giant hoppers.

The vessel then moors about 2km out to sea - its draft prevents it getting any closer - and a smaller Multicat workboat links it up to a pipeline that connects to the shore. The first 300m of the pipeline floats, while the rest of it - about 1,000m long and made of 900mm diameter steel sections previously welded together on the beach - lies on the sea bed.

Sand, suspended in water, is pumped from the vessel along the pipeline to the shore at one end of the beach.

Here it is received in a pipeline made up of 8m lengths of bolted steel pipe laid out on the beach according to where the sand needs to be deposited. Once flows are under way, the operator of a 52t, 360˚ excavator uses the plant’s bucket to help direct sand to where it is needed and to reduce wash away.

It takes about 30 minutes for the area surrounding the end of the pipeline to rise to the required level. Then the excavator and a bulldozer are used to position and connect another length of pipe to lie on the new sand, before the process begins again. The same plant subsequently profiles the sand, a GPS tracking system in the cab making sure that line and level are consistent.

West explains that the dredger comes in on the high tide from the dredging site, to moor 2km out with about 5,000m3 of material on board. It takes about two hours to offload all of the sand into the pipes. There are two high tides a day, but the time of the tide changes by an hour each day.

“It’s all driven by the sea, and the beach crew is geared around that,” says West. That beach crew is smaller than people expect, he adds: just a couple of labourers on the beach plus four machines and their drivers.

24/7 working

Using every high tide means the project has been operating 24 hours a day, seven days a week for about three to four weeks. With the recharge just complete, about 1,000m of beach has been raised by 2m to 3m depending on its location. The rear of the beach is recharged first and the team works its way down to the sea to minimise wash away.

Working with the environment and the local community in mind, dredging is preferable to using quarry-derived sand. The typical capacity of a wagon is just 9m3, so transport from a quarry would need more than 24,000 lorry movements, meaning considerable disruption to the town and obvious environmental drawbacks. The cost of the dredging operation compared to transporting sand by road is broadly the same.

It is a balance between the possible disruption while the work is carried out and the obvious benefits it will produce

Other elements to the scheme, are being carried out at the same time. First is the construction of a new promenade. Working back from the sea, this consists of a sheet piled wall on a different line to the previous one, set below sand level and topped by an insitu reinforced concrete beam; precast reinforced concrete stepped revetment units; a reinforced concrete slab area that will be used for public events; a 450mm high insitu reinforced concrete wave return wall; and new drainage for the road.

There are also extensions to two existing surface water outfalls. Previously, these stopped high up the beach, but now they have been extended to the low water mark and buried beneath the new sand.

Made from concrete, and with reinforced concrete surrounds, the outfall extensions are 180m and 200m long, and 900mm and 800mm in diameter respectively. They will also act as groynes, helping to keep the sand in position.

And public realm works will include improvements to the footpath and tunnel that provide access from the station and town centre passing under the railway and the A55 on the way to the beach. New paving, lighting features, a handrail, access ramp and hard and soft landscaping will be added.

About 100m of existing sea wall will be re-clad with concrete and repaired, and further protection to the wall will be provided by shifting the old rock armour on the beach - some previously used to protect the removed groyne.Such a major project clearly has a huge impact on the local community, but it is a balance between the possible disruption while the work is carried out and the obvious benefits it will produce.

Conwy County Borough Council’s Colwyn Bay Waterfront Project manager Gethin Morgan says there were constraints in terms of working hours, which had to be between 7am and 8pm, to minimise disruption, although the dredging and recharge contractor did apply for an exemption because of the cost involved in a tidal 24/7 operation.

“The locals have been very positive about the disruption,” he says. “In fact the recharging works are going better than expected and will finish sooner.”

The benefits to the local community and economy are clear. A higher beach means that a greater expanse of dry sand is available to the public, particularly at high tide when, previously, the beach all but disappeared. The slab area provides a platform for public events and the stepped revetment improves access to the beach - and it all forms part of a broader regeneration plan for Colwyn Bay.

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