Bid to cut flooding in Hebden Bridge by reducing reservoir levels start again two years after pilot scheme

The pilot scheme to keep the water level lower in reservoirs serving Hebden Water to see if this is a useful flood alleviation measure when extreme rainfall strikes was run by Yorkshire Water at the request of the Calderdale Flood Recovery and Resilience Programme Board.

Hydraulic modelling by the Environment Agency identified such a measure would have benefits, and the intention was to trial it further before a different sort of extreme weather – the drought conditions of 2018 – intervened.

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It involves lowering reservoir levels to 90 per cent rather than being full.

Granville Davies of Yorkshire Water told the board that the company had to make sure it had sufficient resources for its customers but by autumn 2017 the initial trial had been completed.

But when 2018 proved to be largely a hot and dry year, Yorkshire Water spent most of the next year managing drought issues.

By contrast 2019 had been very wet, especially its last six months, meaning stocks were of a height that allowed a second trial to begin.

“So we are looking at another drawdown of the reservoir at Hebden Bridge – the trial started in December and will go through to March,” he said.

“If we get a couple of dry weeks in winter it will allow us to drop those down.”

Coun Jane Scullion (Lab, Luddenden Foot) asked if Yorkshire Water would be piloting something similar anywhere else and Mr Davies said there was a long-standing arrangement with the Environment Agency about Walsden Water but at the moment the one affecting Hebden Water was the only place a trial was being carried out.

Board chair Coun Tim Swift (Lab, Town) also asked about the possibility of a similar test at reservoirs affecting Ryburn Water.

Mr Davies said: “If modelling showed there is benefit we need to look very carefully about it.”

Dropping the level was dependent on weather conditions, he said.

“What we are doing is responding to weather forecasts to try and draw down reservoirs in advance – arrangements are already in place,” said Mr Davies.

As with the winter 2017-18 trial, the drawdown will be done manually by Yorkshire Water’s reservoir resource engineers.

The trial will enable both Yorkshire Water and the Environment Agency to further assess whether it is feasible to operate the reservoirs in this way to offer some percentage of reducing flood risk, whether a long-term change to the operation of the reservoirs is viable and, if so, how the arrangement should be progressed in the short, medium and long-term together with any cons, the board heard.

Once the current work has provided cost estimates, a cost-benefit appraisal will be carried out.

This will include potential Yorkshire Water costs to offset lost water resources and to determine whether the scheme provides value for money.

Further funding will be required to deliver the project – this forms part of the current West Yorkshire Combined Authority “ask” to government for further funding in Calderdale.