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Programme for £1bn tidal lagoon 'tight' says engineer

Building the £1bn tidal lagoon in Swansea Bay within its “tight” three-year programme will require close working relationships, a key figure has warned.

Steve Hutchinson, ports and maritime director at client engineer Atkins, said the Swansea Bay Tidal Lagoon project had little room for contractor error.
Hutchinson spoke to NCE after the project was granted a development consent order by the government.

“It is a tight programme and will require careful planning and good working,” he said.

“There are lots of interfaces between contractors and we can’t have one contractor delayed by another. There is a high requirement for health and safety and co-operative working.”

The project involves building a 9.5km sea wall - or bund - to create a lagoon, which will contain 16 turbines that will generate about 500GWh per year of low carbon electricity.

The power station itself will be the turbine house built 2.5km from shore where the sea bed is 4m below the water level at the lowest tide.

“This type of construction has been done before - but the length of the bund is unusual,” said Hutchinson.

“The turbine house is a concrete box - but it’s in an unusual location.

“It’s heavy construction. There are 300,000m3 of concrete, primarily for the turbine hall; 3M.m3 of quarry-run and rock for the bund; and 3.9M.m3 for the bund core.

“It will be a challenge. If anything restricts the access then it causes delays. “We are working at sea and there will be wind and storms.”

The bund - made from sand, rock, geotextiles and a paved surface for public access - will be built in two stages.

“The western bund will extend 2.5km from the coastline, then a cofferdam will be built at the end of that, sheet piles installed within the cofferdam, and then there will be dewatering equipment,” said Hutchinson.

“We will pump the water out of the cofferdam, expose the sea bed and excavate to minus 17m chart datum.

“The turbine house will be a big concrete box that houses 16 low-head Kaplan turbines, each with a 20MW rated capacity.

“There will be 16 draft tubes to funnel the water through the turbines and eight sluice gates to allow water in and out when the water difference is too low.

The turbines will generate for 14 of every 24 hours.

“The turbine house will then be flooded so the turbines can be wet commissioned.

“We will also be building the eastern bund and eventually closing the gap between the two, which is difficult as the water is being forced through. You stockpile rocks and push it in with heavy plant as quickly as you can.”

Atkins is currently evaluating designs by the project’s preferred bidders to make sure they comply with project promoter Tidal Lagoon Power’s concept.

Hutchinson said the challenge was unique.”It is an interesting, challenging process,” he said. “It is the type of project you dream about. No-one has done anything like it before.

“There is a tidal power lagoon in Korea and one in France but they only work on one tide; this will be ebb and flow, which brings challenges in making sure the turbines spin both ways.”

Andrew McNaughton, director of engineering and construction at project promoter Tidal Lagoon Swansea Bay, today told NCE offsite construction techniques would be used where suitable on the Swansea Bay scheme.

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