UK to Build 10 Mile-Wide Tidal Super Dam

A massive tidal power project at the mouth of Great Britain's longest river could create a 10-mile wide, $15 billion (in pounds) dam that would generate 17 terrawatts of electricity per year.

I've always been a sucker for giant engineering projects, from classics like the Great Pyramids to modern marvels including Dubai's world-shaped islands and Taipei 101. I'm not interested beating nature into submission or one-upmanship, but about physically demonstrating humanity's collective intelligence, effort, and drive. The Severn project in the UK combines my build-lust with another obsession: green power.

Developers have had their eyes on the Severn estuary since the late-19th century, first for a shipping harbour, then various electricity projects. The high costs of such daunting engineering has kept these plans from realization, but is now moving ahead.

Two possible versions of the tidal power plant exist, a dam-like barrage and a man-made lagoon. The barrage would let water enter during high tide, trap it, then release it through 200+ giant turbines to generate electricity. The lagoon option, favored by some environmental groups, would feature a number of lakes that would fill and empty through turbines and cover only about 60% of the land area of the barrage.

The barrage option appears to be the most likely, with a detailed plan that's existed since 1989. The next hurdle for the Severn plan is a Strategic Environmental Assessment, which will determine how the surrounding environment will be affected.

The scale of this project is staggering. The span, to double as a bridge between England and Wales, would be more than twice as long as the Chesapeake Bay bridge in Maryland.  According to the Times Online, construction would require moving 18 million tonnes of seabed and 13 million tonnes of concrete, gravel, and other material. To top it off, the design has built-in locks for letting ships pass.

Although UK government officials say the proposal could meet up to 4% of the United Kingdom's electricity needs renewably, it has been opposed by environmental groups such as WWF, Friends of the Earth, and the haughty-sounding Royal Society for the Protection of Birds (RSPB). And they have a point. The estuary is a protected conservation area and RSPB says an annual average of 65,000 water birds call it home. Damming the area would threaten the sensitive inter-tidal area.

My guess is that the project will go forward, especially with the UK wondering exactly how they'll meet their target of 40% renewable electricity by 2020. As with many of the great building efforts of the past, there are trade-offs between earth and earth-moving, even when you're doing the latter to preserve the former.