Ipswich Tidal Barrier

Purpose

The purpose of the project was to design, fabricate and install a 20m-wide sector steel barrier gate that could be closed during a flood event. This was a flagship project for the Environment Agency, being the first rising sector gate constructed in the UK since the Thames Barrier was built in 1982.

What we did

We designed, fabricated and installed a 20m-wide rising sector steel barrier gate across the New Cut of the river. We also raised the existing defences on either side of the new barrier.

We brought together 12 designs from multinational suppliers into one federated 3D model. This meant we could visualise the complex integration of the civils, gate and MEICA designs.

We first constructed a sheet-piled cofferdam to provide a safe and dry working environment. We offset its position to allow vessels to continue passing safely throughout construction.

The gate sits within a huge concrete holding structure. Before dewatering the cofferdam and adding temporary props, we drove 48 tubular piles into the riverbed to provide a solid foundation for the gate’s heavy concrete base.  We then cast a 1.5m-thick concrete base across the cofferdam’s width and 5m-thick walls on either side against the cofferdam’s sheet piles, which we retained as part of the permanent works. We then cast gate anchors.

In the meantime, the 200t steel barrier gate was fabricated at a specialist facility in the Netherlands. It arrived on site in November 2017 and was lifted into its base with a 600t crane. Subsequent testing vindicated our 3D model by showing that it fit within a 2mm tolerance.

After completing testing and removing the front and back cofferdam walls, we diverted the channel through the structure, with the gate sitting on the riverbed when not in use. We then constructed new sheet piled river walls out to the gate on its western side.

We stored, treated and reused dredged material as fill, eliminating the need to import virgin material. We dried it within huge geotubes and mixed in waste cement dust to create a suitable backfill material.

We also constructed a MEICA control building, installed flood gates on both banks, added scour protection and landscaped the entire area.  

Project successes

The barrier now protects 1500 residential and 400 commercial properties in Ipswich from flooding.

We delivered the project within its allocated budget, which was important, given the significant contributions made by partners Ipswich Borough Council, New Anglia Local Enterprise Partnership, UK Power Networks and the Government’s Growth Fund. £2m of engineering efficiencies helped meet this goal.

Our value engineering proposals during the design phase made the gate easier and safer to inspect and maintain. By assessing its movements, and adding a second pin connection, the gate can rotate 180o out of the water into its maintenance position, without the cost of crane hire or potentially risky diving operations, which would have been necessary with the original design’s limited movement.

The project team saved time and reduced waste through a variety of innovations and engineering efficiencies. These included a fundamental review of the gate’s geometry and function, a redesign of the piled foundations, reuse of material (e.g. dredge arisings), change in design from sheet piled floodwalls to CFA walls with seepage drain, using lost tip pile heads to install 14 cofferdam dewatering wells, removing eight tubular piles from the original design, and a drive to minimise waste off site, with 99% of waste by weight diverted from landfill.

As a result of our efforts, we won the Civils Project of the Year at the Constructing Excellence SECBE Award in 2019. After winning the award Andrew Usborne, from the Environment Agency, commented: “This is fantastic news for everyone involved, including all the Environment Agency staff, our contractors, VolkerStevin, and sub-contractors. It has been a hugely successful construction project, one which is being used as an example to other Environment Agency schemes across the country of safe and effective partnership working."

We also won a Considerate Constructors Scheme (CCS) National Silver Award; the Institution of Civil Engineers (ICE) presented the team with an Exceptional Merit Award for Technical Excellence and Innovation, and the project was a Climate Resilience Project of the Year Finalist in the British Construction Industry awards.

In addition to the successful delivery of the flood defence, the scheme has provided a multitude of enhancements to the local community and businesses.