There is no place on earth, no matter how remote, untouched by humans. We are mighty: we can trawl the deep, explore the South Pole, and fish every single island in the South Pacific. But as every young nerdling knows, with great power comes great responsibility. “The Managed World” series in the Oyster’s Garter explores the hard choices that come from a human-dominated world.
Science Magazine reports that the UK is pondering the world’s biggest tidal power generator. The Severn estuary, which separates southwest England from south Wales, has the second-biggest tidal flux in the world – the water rises and falls 45 feet (15 meters) between high tide and low tide. That’s a huge amount of power, and Britain wants to builf a tidal dam, or “barrage”, to capture it.
A barrage is a huge dam, similar to a hydroelectric dam, built across an estuary. The Severn barrage is designed to let water freely flow into the estuary through sluice gates, which would then close to impound water in the estuary. The water would then slowly be let out through turbines. Locks can be built to let ships through, but there’s no channel for water critters except through the turbines.
The ecological impacts could be vast and devastating. Over 68,000 birds overwinter in the Severn estuary, feeding from mudflats at low tide and sheltering in marshes. The barrage would essentially eliminate low tide, flooding these habitats and making them unavailable to birds. Also, many species of fish and invertebrates migrate into estuaries to breed, and the barrage could either prevent adults from migrating in or trap the larvae inside. Because of these vast negative impacts, it’s not surprising that Britain’s largest environmental groups have rejected the Severn barrage plan.
However, there’s no way the UK will be able to meet the EU’s goal of 15% renewable energy by 2020 without some drastic changes. Currently, only 5% of the UK’s current power is renewable. The Severn barrage alone would provide another 5% of the UK’s total energy, in reliable, carbon-free, and low-maintenance form. The only comparable barrage, the La Rance Tidal Power Plant in France, has been in operation for 40 years without a breakdown. This type of cheap, reliable, carbon-free power is pretty tantalizing, even at a hefty construction cost of £15 billion and the abovementioned environmental costs.
So again, well-intentioned people have to choose – carbon-free energy, or giant critical habitat estuary? This is the that we must reduce emissions – we are already surpassing the IPCC worst case scenario. But estuaries are critical habitat for hundreds of thousands of species and provide important ecosystem services such as flood control and pollution filtration.
One potential angle that I did not see discussed in my uncomprehensive readup on the Severn barrage is the potential for estuaries to act as carbon sinks. Because estuaries (and mud flats) have little oxygen in their soil, plant matter gets buried and doesn’t decompose for a long, long time. How much carbon is buried in the Severn estuary, and would the barrage release it? This might be one way to decide whether the energy generated by the Severn barrage would be worth the ecological damage.