Boston Barrier Scheme

How the Boston Barrier scheme was built

The project used the UN Sustainable Development Goals (SDGs) to monitor and evaluate its success.

Using SDG 12 - responsible consumption and production - helped the team identify various savings.

Carbon savings

The centrepiece of the scheme is the primary barrier gate. 

This is a 362-tonne, 26m-wide and 11m-high rising cill sector gate that's raised into position by two 55-tonne hydraulic rams to defend against tidal surges.

The forces exerted by the gate during these movements required a structure that was strong enough to form a unique design to accommodate the curvature of the barrier gate.

It also needed to meet the 100-year design life of the barrier. The only viable solution was in-situ and precast reinforced concrete, which would have resulted in a carbon-intensive project.

To make carbon savings in the barrier structure, the concrete mix incorporates 70% ground-granulated blast furnace slag (GGBS) as a cement replacement.

For every tonne of cement, about 860kg of carbon is produced, compared with 79kg per tonne of GGBS (which is a by-product of the iron industry).

In addition, GGBS is cheaper than cement and results in a dense concrete with good chemical resistance.

Another carbon-saving design decision was extensive 3D CAD modelling to enable clash detection, to verify the design and ultimately avoid rework required onsite.

The Environment Agency’s Ipswich barrier team, whose flood barrier opened in 2019, were instrumental in this decision-making.

By sharing lessons learnt and key knowledge, the Ipswich team, who had cast their gate recess onsite, suggested that prefabrication could simplify the process.

The Boston team’s solution was to generate 3D models for the 24 precast gate recess components, which were subsequently installed in three days.

Scheme contractor BAM Nuttall/Mott MacDonald JV (BMMJV) also ordered prefabricated bespoke rebar cages, which cut the base slab reinforcement installation time from two months to two weeks.

Other savings included the potential to reuse dredged material as backfill and as capping at a local landfill site. This adjustment saved more than 30,000 lorry movements (and their associated emissions).

Time savings

By pre-casting the primary gate’s recess and ordering large, prefabricated reinforcement cages, a total of seven weeks were saved.

This also significantly improved the health, safety and wellbeing of the workforce during installation and reduced the need to work in confined spaces.

In addition, the site investigation, backed up by a settlement load test onsite, showed that the ground was suitable for shallow foundations.

This meant that approximately 70 steel tubular piles could be removed from the scope of the project.

This saved 360 tonnes of embodied carbon and £300,000 in project costs. It also reduced construction time by four weeks and shaved three weeks off the design programme.

Energy savings

The roof of the barrier’s control building also features 32 photovoltaic (PV) panels, which provide a 9.6kW renewable power supply.

The PV panels deliver 16% of the control building’s electricity, with a saving of £550 per year and a carbon offset of 2,000kg CO2e per year.

An air-source heat pump was also installed, which reduces the control building’s electricity use by 25% compared with traditional electric heaters.

This equates to annual electricity savings of £2,200 and an annual carbon offset of 4,100kg.

Difference the project has made

The Boston Barrier scheme provides better protection for thousands of homes from tidal flooding and will continue to do so over the next century.

But the project is more than just a flood defence.

It's been estimated that the scheme could help to deliver over £1 billion in economic benefits to Boston town and the surrounding area by encouraging investment, improving resilience and wellbeing, and protecting historic assets.

The construction team made it a priority to spend locally where they could, investing millions of pounds in the local economy within a 50 mile radius of the site.

The scheme also includes works to tie the project into the Haven Banks Improvement Scheme.

This is a separate Environment Agency project downstream of the barrier site which raises and strengthens 5km of existing flood banks on each side from the primary barrier towards the Wash (an inlet to the North Sea).

Engineering skills used on the project

• Civil engineering
• Mechanical and electrical engineering (MEICA)
• Geotechnical/ground engineering
• Project management and site management
• Environmental engineering, including carbon offset and mitigation
• Design – BIM, federated models, 3D and virtual design
• Construction skills – concrete, steelwork, reinforcement, precast and prefabrication
• Site development and spatial planning for confined sites and shared spaces
• Structural steel design – primary gates, structural gates, building design, sheet piled walls
• Hydraulic high pressure design and fabrication in stainless steel