Norfolk’s new £121m bridge has increased the risk of flooding on the Broads, official documents show.

A report commissioned by Norfolk County Council when it was considering building the Herring Bridge across the Yare in Great Yarmouth acknowledged that the structure would lead to an "increase in water depths on the floodplain... during a flood event".

This was because the bridge is built on two abutments, or 'knuckles', which narrow the river by more than a third, restricting the amount of water that can flow out to sea.

The 2019 documents have surfaced after people living in Broads villages suggested the extensive flooding they have suffered in recent weeks could be partly due to the bridge.

The council insists the crossing is not a significant factor and has pointed out that a government-appointed planning inspector dismissed concerns about an increased flood risk as "negligible" when giving the scheme final approval.

Beccles & Bungay Journal: Breydon WaterBreydon Water (Image: James Bass)

However, the studies carried out into the issue only looked at the impact of the bridge on Yarmouth and nearby Breydon Water and critics say they overlook other low-lying parts of the river network, including several rivers which do not flow into Breydon Water.

WHAT IS SO SIGNIFICANT ABOUT THE BRIDGE?

The crossing is about a mile from the mouth of the Yare, the only outlet into the North Sea for the entire Broads network of waterways.

The bridge has two 'knuckles' that jut into the river from either side, restricting its width from 89 metres to 55 metres.

Water levels on the Broads have been extremely high in recent weeks, with flooding in many areas, as a result of long periods of heavy rain and high tides.

Villagers living along the waterways say that over the last two years, since construction started on the bridge, levels are taking longer to recede than in the past.

They have suggested that the crossing could be reducing the amount of water that can flow downstream on each tide, prolonging the flooding.

WHAT DO THE DOCUMENTS SAY?

The documents were drawn up by consultants commissioned by County Hall as part of the process to secure the government green light for the project.

Among a list of "likely significant effects" of the bridge, they warn of an: "Increase in water depths on the floodplain and receptors during a flood event due to constriction of flows caused by bridge knuckles."

The issue was also discussed at a later public inquiry to decide if the scheme should go ahead, after it was raised by the Royal Yachting Association.

But the council's consultants said the risk was "negligible" and the planning inspector said the Environment Agency had not requested a wider river flood scenario in the assessment.

The inspector concluded: "The evidence does not support the contention that the proposed development would increase water levels upstream or lead to flooding of the higher reaches within the Broads basin."

They added they were "satisfied that these matters have been appropriately assessed and considered as part of the flood risk assessment and the scheme would not lead to an increased risk of flooding in the Norfolk broads basin".

Beccles & Bungay Journal: The Herring BridgeThe Herring Bridge (Image: Mike Page)

The 2019 studies only considered the possible flood impact on Yarmouth and the vast Breydon Water, about a mile upstream of the bridge.

The council say because the flood risk there was considered 'negligible' it was not necessary to consider what the effect could be elsewhere.

WHAT DO VILLAGERS SAY?

Critics say the failure to consider the risk beyond Breydon was a mistake.

It meant that the impact of the bridge on the so-called northern rivers - the Thurne, Bure and Ant - was overlooked.

These rivers all empty into the Yare between Breydon and the new bridge and locals say the outflow is severely restricted by high water levels on the Yare which in turn is affected by the new bridge.

Beccles & Bungay Journal: Flooding at Potter HeighamFlooding at Potter Heigham (Image: Mike Page)

One local - who is considering a class legal action against the council on the issue - said: "We have to go back to around 2013 before we can all remember a similar flood.

"That was after far more rainfall, it only lasted about three days and was tide-locking pure and simple.

"This is not now tide-locking in my view. It is a man-made restriction to the river flow, so even when we are not tide-locked, not enough water can get out to sea to provide a meaningful reduction to flood water.

"That means that in mid-October and again in mid-November, even with a series of low ocean levels at both tides and little or no rain to add to the surface run-off, the flooding never receded completely in several weeks.

"This is all a new feature of the past two years, with construction of the pontoons beginning to restrict the river during late 2021, with the effect clearly seen on river heights in Wroxham, particularly the way it falls between high and low tides."

WHAT DO OFFICIALS SAY NOW?

The authority insists that because the Breydon flood risk was low, the bridge cannot be responsible for recent flooding in villages such as Horning, Hoveton, Wroxham, Potter Heigham, Surlingham and Geldeston.

READ MORE: Norfolk river levels likely to stay high for three weeks

It says this is due to excessive rainfall after storms and what is known as tide-locking, where a series of high tides prevents water draining properly.

Beccles & Bungay Journal: Graham Plant, Norfolk County Council cabinet member for highways, infrastructure and transportGraham Plant, Norfolk County Council cabinet member for highways, infrastructure and transport (Image: Newsquest)

Graham Plant, Norfolk County Council's cabinet member for highways, infrastructure and transport, said: "Any flood risks to the broads were extensively modelled as part of the design process for the Herring Bridge.

"The independent examiner was fully satisfied with the work carried out in granting the development consent order following the public examination and concluded that any potential impact from the bridge was negligible.

"No objections were raised by the Environment Agency or the Broads Authority and there is nothing in the evidence presented or any recent tidal data to suggest otherwise.

"The study area didn’t extend beyond Breydon Water because, if there is no impact on Breydon Water, there cannot be an impact further upstream. The bridge knuckles have been in place for over two years."

An Environment Agency spokesperson said: "The Great Yarmouth Third Bridge Crossing was submitted to the Planning Inspectorate as a Development Consent Order by Norfolk County Council.

"The Environment Agency was consulted and had no objections to any flooding impacts arising as a result of the bridge.
 
"The width of the river at Herring Bridge is approximately the same size as at Haven bridge, which is an older bridge upstream of Great Yarmouth and closer to the Broads.”

The Broads Authority said: "The most recent flooding, as we understand, was due to October’s rainfall being higher than average, in conjunction with several days of surge on top of a neap tide constricting rivers draining through Great Yarmouth.

"Such events might become more frequent with climate change."