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Construction milestone hit on £100M Boston flood barrier

Birdseye view of cofferdam

Temporary works have been completed ahead of the construction of a new 25m floodgate across the River Witham in Lincolnshire.  

The cofferdam, which will allow the construction of the new Boston flood gate, was built by Mabey Hire and installed by engineers from Bam Nuttall.  

The design had to compensate for varying currents and tide levels of the water surrounding three of the cofferdam’s four walls. To stabilise the structure, bespoke box sections were created and welded to the rear of the frame, which sit in the pan of the sheet pile wall to ensure the eccentric loads are distributed around the cofferdam walls. 

The construction of the floodgate will be carried out by project leaders Bam Nuttall and Mott Macdonald Joint Venture (BMM JV) on behalf of the Environment Agency.  

Bam Nuttall project director Steve Lowder said the varying loads presented a challenge in putting the cofferdam in place. “Working with a cofferdam is always tricky, let alone with the added challenge of varying and significant loads due to the tide range and the depth of excavation.”

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Boston Barrier Project

Render of completed floodgate

He added: “Mabey Hire’s rapid strut design enabled us to secure the cofferdam as quickly as possible, so excavation work could progress quickly, safely and efficiently. We look forward to delivering this vital flood prevention scheme, which will protect thousands of homes and businesses from further flood damage.” 

The scheme was first approved by the government in December 2014, but delayed after the Port of Boston opposed a Transport and Works Act application made by the Environment Agency in August 2016. The Port formally withdrew its objection in March 2017 allowing the barrier to progress to a public inquiry. 

When complete, the 25m wide, hydraulic-powered barrier across the River Witham will protect around 14,000 homes and businesses from flooding. The town suffered severe tidal flooding in December 2013 when more than 800 properties flooded across 55 streets. Flooding also occurred in 1953 and 1978. 

The project is expected to be delivered in early 2021.  

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