River 'fence' to harness tidal power of Mersey

It has been better known over the past 50 years for lumbering ferries and the leaping salmon which are returning in droves. But the river Mersey is now to be subjected to tests which environmentalists hope will make it the first river in Britain to generate electricity from its tides.

A renewable energy conference attended by Sir Jonathon Porritt will be told today of plans to draw on the Mersey's vast renewable energy potential by constructing a tidal power fence which, according to initial estimates, could generate up to 2,000 megawatts of electricity, enough to power 15 per cent of the North- west's electricity requirements.

The Mersey offers more tidal power potential than virtually any other river in Europe, by virtue of its 10-metre tidal range and strong currents which are a by-product of its shape and its position on England's windy North-west coast.

Peel Holdings, the property company which recently acquired the Mersey docks, has agreed to make land available to construct a fence across the width of the river. Water would be trapped in gates, which would be shut at high tide and then allowed to escape through the turbines of a hydroelectric plant.

The model for such a project is the tidal power station at the estuary of the La Rance river in Britanny, France. Built in the Sixties, it delivers about a fifth of the output of a nuclear or coal-fired power plant and more than 10 times the power of the world's next largest tidal station - the 17-megawatt station at the mouth of the Annapolis river in Canada.

The idea of a tidal fence, or dam, is not new to the Mersey. A similar Mersey barrage project caused huge controversy in the early Nineties, when ecologists were angered by the disruption it would cause towading birds feeding on the mudflats. They were ultimately placated - but the project's inability to offer a quick financial payback still led to it being scrapped. A similar fate has befallen attempts to construct something similar across the Severn estuary.

But environmentalists are confident that Britain's acute need to create energy without carbon dioxide and hit the Government's renewables obligation of 10 per cent output by 2010 may create greater acceptance this time. Peel's involvement also promises to deliver a private sector rigour. The dam's financial and environmental costs would also be reduced by positioning it further inland than the 1990s barrage and making it narrower.

"The technological opportunity is uncontestable, here," said Walter Menzies, chief executive of the Mersey Basin Campaign, which will deliver news of the dam study at its annual conference. "We are seeking to establish which mix of technologies might get the most economic return. The national position is that there is a huge push for renewal energy yet we are a long way off targets." Though tidal power stations can only generate when the tide is flowing in or out (10 hours a day), tides are predictable so the projected returns can be met and other power stations can ensure continuity of supply.

The North-west does not lack ambition when it comes to harnessing power from the tides. Plans have been lodged in the past year to build a bridge across Morecambe Bay and insert Canadian-designed vertical axis turbines in its stanchions to harness tidal energy. The project is currently being tested by Lancaster University and has the support of British, Dutch and Australian investors. Scientists at Manchester University are also testing a model to convert energy out of the pressure differential of waves.

The scale of the Mersey project would be considerably bigger, and one local environmental source suggested yesterday that it might need to incorporate a third Mersey road crossing to attract investors. "The payback time on these projects is so long, it needs good revenue generation capacity and road use might provide the attraction which investors would need," he said.