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Flood scheme is on target

Boston Barrier is a BIG scheme. Everything about it is gargantuan - the cost, the materials, the kit, the manpower, the construction site. It's all on a colossal scale.

Its impact will be similarly massive. The £100 million scheme is deemed a 'National Priority Project' within the Environment Agency's Six Year Programme and is fully funded by Government Flood Defence Grant in Aid. Once built it will reduce the risk to more than 14,000 properties from tidal flooding. It is being built beyond the threat of a tidal surge such as the one which engulfed large parts of Boston on the night of December 5, 2013.The tidal river bank is also being raised as part of a separate Environment Agency project downstream of the barrier all the way to the mouth to afford protection to properties there, also beyond the limits of the 2013 flood. It's the biggest flood protection scheme outside of London.

Some may have thought they would never see the day when such major investment would be made in Boston, but construction of the £100 million barrier began after Government approval earlier this year.. BAM Nuttal and Mott MacDonald Joint Venture (BMM JV) won the £75 million contract to build the barrier last year and started preliminary work for the scheme soon after.

The barrier itself will be installed by next December with the project as a whole due to be complete by winter 2020.

Nearest neighbours to the works will be pleased that the noisiest works have now  come to an end - steel sheet piling driven into the river bed to create  a cofferdam and bankside reinforcement is now complete on the south bank and secondary piling will continue in the New Year.

The contractors at BMM JV designed and installed a five-metre high temporary noise shroud for the properties directly adjacent to the works along Wyberton Low Road which has reduced noise levels on the street considerably.

A huge working platform, floated into place and then jacked up from the river bed, much like an oil-drilling rig, equipped with heavy-duty piling and vibration hammers, has been used to drive more than 2,000 tonnes of steel piles metres down into the river bed. A rocky strata below the oozing mud did its best to resist the steel sheets being driven into it but man and machinery persisted and prevailed.

The cofferdam, which extends from the bank across about two thirds of the river is opposite the port and just downstream of the Forty Foot outfall. When it has been dewatered, work will begin to install the concrete base across the river bed for the giant steel flood protection gate.

Expert and experienced flood protection engineers at Hollandia in the Netherlands are constructing the giant gate, which will be delivered by ship to the site from across the North Sea.

It will be the final piece of a giant jigsaw - the massive hydraulic rams which will raise the barrier  will already be in place waiting to receive the gate. Unlike  some hydraulics used for other flood protection projects, Boston's rams won't be as submerged and at a more horizontal angle, to reduce salt water corrosion. This  will also mean they are less of a dominant feature on the landscape when not in use.

At such times the barrier will rest in a recess flat on the river bed, allowing boats to pass safely above it.

An 18 metre navigation channel has been left open on the Port of Boston side of the cofferdam to allow vessels to safely pass the construction site and a safety boat has been deployed to enforce one way traffic during the construction works, and those making passage through to The Wash get a seal's eye view of the construction.

Boats from Boston's fishing fleet have been berthed temporarily on the seaward side of the construction site and will return to their normal mooring on the town side when the project is complete.

A heightened flood gate will also be installed at the port entrance downstream of the barrier.

The current bypass channel will eventually be filled in, narrowing the river at that point, so that when the barrier is lifted to deal with a flood alert it will completely block the passage of water up the river.

The barrier was initially designed to be multifunctional and can still be utilised for water level management at a later date, which could see water levels held at an attractive height throughout the town. If subsequent approvals went ahead the scheme has a sterile area provision to allow for a lock for Water Level Management in the future.

Cllr Michael Cooper, Leader of Boston Borough Council, said: "No one who was affected by the horrendous flood of December 5, 2013, wants reminding of that horrendous night and the days, weeks and months afterwards. But the good news is that Boston is now to benefit from a truly massive flood protection scheme. It is a massive investment in the area, providing added security and peace of mind for literally thousands of property owners. It opens up a whole bright new future for economic development and, given the scale of the project, it has proceeded at pace. We all look forward to it being fully operational."

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