More than 500 million cubic metres of water will be extracted from the River Taff by giant screw turbines if a licence application by Cardiff council is granted.
The authority has submitted a 16-page proposal to the Environment Agency outlining its plans for hydro-electric power generation at Radyr Weir, a popular picnic spot on the River Taff in Cardiff.
It will see “reinforced concrete chambers” dug into the channel to fit the where the turbines will be mounted.
According to the paper, it will look like “an extremely large hardware screw.”
Called an “Archimedes’ Screw” it dates back to the third century BC and is used to draw water.
“It was first used as a water pump, with the screw rotating to lift water uphill,” the document states.
“The potential of inverting this process has now been realised, by allowing water to fall by gravity into the chambers of the screw.
“The system then rotates, allowing potential energy to be extracted from the water and fed through a gearbox to power a generator to export electricity.”
It will be able to turn at 1,500rpm. According to the authority, it is “potentially fish-friendly”.
A temporary fish pass would be built at the site while the work is carried out to ensure salmon are able to migrate.
Each year the council says water totalling 513,216,000 cubic metres will be taken from the river before being returned downstream.
The plan says: “The amount of water to be abstracted from the river must be controlled to comply with the conditions set out in Environment Agency licences and consents to ensure that ecological, fisheries and other water interests are not compromised.”
In February it was estimated the scheme would cost £1.5m, although it is unclear whether that figure was still accurate.
The 400KW system could generate enough energy to power three of the city’s leisure centres – and save 700 tonnes of CO2 – per year.
A spokeswoman for Cardiff council said: “These are all significant details that we are not in a position to fully answer at this stage.
“However, if all the necessary consensus are secured, we hope some form of start to the programme will commence next year.”