New pumps could raise river levels

It has emerged that new pumps in the Foss Barrier - funded and installed since the Boxing Day floods of 2015 - could see water levels downstream get higher, and engineers are now looking at ways of protecting homes in those areas.

The Environment Agency has produced a flood defence update for City of York Council, setting out progress with millions of pounds pledged by ministers for York.

The report shows some of the improvements could have unintended consequences.

The new higher capacity pumps can cope with 50 cubic metres of water per second (cumecs), a major improvement on the 30 cumecs the old pumps could move.

The report says: “The Foss Barrier modelling scenarios show that the increase in pumping capacity from 30 to 50 cumecs could lead to increased river levels on the Ouse immediately downstream of the barrier of eight centimetres during a worst case scenario.

“This could have implications for low-lying properties in the Fishergate area and across the river in Clementhorpe.”

Council environment boss Andrew Waller will receive the report at a public meeting next week. He said he had long been aware of potential problems should both the Ouse and Foss flood at the same time, and had been pushing the Environment Agency to come up with the funding and the engineering time to look for a solution.

He and councillors for both Fishergate and Clementhorpe agreed the threat is more severe in the low lying streets west of the Ouse.

Cllr Johnny Hayes, whose Micklegate ward covers Clementhorpe, said places like Lower Ebor Street could be at risk, as flood walls there came very close to being over-topped during the 2000 and 2015 floods. An extra 8cm could be crucial, he said, and as Lower Ebor Street sits in a basin the area would flood quickly if the defences were overwhelmed.

Although the Environment Agency plans to start work on new defences next summer, Cllr Hayes said people in the area want to know something is in place before this winter arrives. Even temporary measures would help people feel safe from flood waters, in case the winter of 2017 sees a repeat of 2015.

The cost of demountable defences is in the tens of thousands, but the cost of repairing people’s homes in the hundreds of thousands, Cllr Hayes said, so they cannot be ruled out on cost grounds.

An Environment Agency spokesman stressed that the 8cm increase in water levels was a “worst case scenario” which would only occur during extended floods “far worse” than December 2015.

He added: “The schemes on New Walk and Clementhorpe will be amongst the first to be carried out as part of the Environment Agency’s five year plan for York, with survey works starting in the coming weeks and construction starting in 2018.

“It’s important that we carry out in-depth site investigations before construction work begins.

“These works will mitigate against a potential increase in water levels as a result of the increased pumping capacity of the improved Foss Barrier.

“In the interim we will use the information from our modelling to inform our operation of the Foss Barrier to ensure there’s no increased risk to properties downstream.”

Meanwhile, it has emerged that Naburn Weir is unlikely to get any changes, but a hydropower company is eyeing the site.

A separate Environment Agency report shows that while changes at the weir could lower the water levels in York slightly during a flood, they are unlikely to make enough difference to be worth the cost.

Only removing the weir entirely would make a significant difference - bringing the river level down by between two and 10 cms in central York during a full flood - but lowering the water when river levels are normal would have a dramatic and detrimental effect on navigation, bank stability, biodiversity, and aesthetic value, it adds.

However, the report also reveals that a hydropower company is interested in Naburn Weir, and the Environment Agency has been sharing information with the firm.