Plans favour Welsh shipping

“This thorny subject crops up with the same regularity as myths like the third runway at Heathrow (first proposed 1946) and the Loch Ness monster. It will take decades and fortunes to design and build, after which we will see the real effects, rather than the theoretical computer modelled effects.

If it is technically feasible to build the barrage, it is technically simple to include locks to take shipping of the size envisaged for the Avonmouth Deepwater port, and bigger, to future proof it. We would lose the Severn Bore, but also the dangerous currents, something that may positively benefit Avonmouth. We could also have a rail link (preferably) or road over the barrage. Hinkley C would be unaffected, and we would generate 5% of the nation's energy need with much greater certainty than the folly of wind farms would ever offer. We don't have much by way of hydroelectric power (I know this is tidal, so different), and this gives the opportunity to exploit a true renewable source of energy with a potential we can predict by the minute over a period of centuries.

We could, of course, also end up with a rapidly silting up putrid reservoir, its increasingly frantic fleet of dredgers fighting a futile battle against the elements, with the Severn becoming a marshland from Gloucester upwards, a landlocked Avonmouth Dock, no eels, no River Avon (twice) no wildfowl anywhere to be seen, and a £30 billion white elephant that generates enough to power half a dozen toasters. It would make Bristol's stupid £50 million BRT2 route look like a good idea, something I thought impossible this morning.

There are only 7 tidal power stations in the world, only 4 of which operate on the same principle. The Rance barrage in France is probably the closest in technology to this idea, and is tiny by comparison. All have had environmental effects of an undesired nature, although most have been engineered out, with two exceptions. Strangford Loch in Northern Ireland employs a small scale non-barrage tidal flow system that has negligible environmental impact, but produces little power - it is the test rig for bigger tidal flow systems. Sihwa facility in South Korea produces more power than the Rance, although it was actually constructed to cure pollution behind a sea defence, and the power generation is a welcome by-product.

Remember that the construction of the Floating Harbour caused a cholera epidemic, giving Georg Muller a reason to open orphanages, and Isambard Kingdom Brunel a chance to prove himself the most versatile engineer by constructing the Underfall Yard, and you realise that there is a huge potential for an unintended consequence here. Some may be positive - we could maybe fill in the New Cut in Bristol, and build "affordable" housing or a Bus Rabid Transit route. Others could amount to an ecological disaster of incredible proportions.

I am not, unusually for me, going to offer an opinion either way. The potential may be enormous, but the risk is even higher. Politicians drawing lines on maps and asking greedy investors to build some form of subsidised infrastructure is not the best way to go about this. You only have to look at the rush to build wind turbines whilst we dither over useful solutions, or the stupid £50 million BRT2 route, to realise that this needs proper scientific and engineering study at the highest level over a number of years, including smaller scale projects and testing of possible alternatives.

This project, if fully committed to, fully funded, and freed from pressure from any source, will take 20 years to deliver, at least. A government lasts for only five years. It hasn't the vote-losing potential of nuclear, shale gas, or wind, but it may have soon. The real consequences, be they financial, environmental, or social could be worse still. Or better.”