This page was updated on 16th September 2013.
Topical: Severn Estuary ... written August 2008
Severn Tidal Barrage Proposal(s)
Watch this one carefully. If it is to go ahead the government, or whatever agency they get to front it, will have to present some convincing science. This will be difficult!
The Severn Estuary, like most macro-tidal estuaries in Britain, contains a large amount of cohesive sediment. This is sticky mud to most people. Not only is it sticky but much of it is also highly mobile. It moves around the estuary driven by tidal flows and meterological influences. Despite several decades of scientific investigation by oceanographers, physicists and biogeochemists there is no satisfactory method of predicting what will happen to the many millions of tons of sediment if large structures are placed in the estuary.
Several organisations are keen to convince us that they can predict the sediment dynamics. They will base their arguments on their "numerical models". These are numerical simulations of tidal dynamics onto which sediment dynamics are piggy-backed. Tidal dynamics can be successfully simulated in deeper water but such simulations develop errors in shallow water. Sediment dynamics is very poorly simulated on computer for a number of reasons. Flocculation, resuspension and friction are all difficult to simulate in estuaries. If someone tries to assert otherwise they are either naïve or not declaring all the caveats.
With these fundamental problems is it really worth spending billions of pounds of public money on pouring millions of tons of concrete and lots of rock into a natural estuary? A very expensive engineering experiment. When it devolops problems, who will take the concrete out and restore the estuary to a natural equilibrium?
As for generating five per cent of Britain's electricity, was this calculation done by an accountant, a politician or an optimist? Were they privy to "tidal friction". Is the five per cent something of a convenient "rounding up"?
Sediment dynamics has received intermittent research funding from governments around the world. One of the drivers has been the need to get bigger ships into estuary ports without excessive dredging costs. It is a pity the research funding isn't sustained because estuaries are one of the most complex fluid environments on our planet. The study of flocculation and resuspension, particularly, in estuaries is also valuable for better understanding of anthropogenic pollution transport...
Several nations are studying other ways to sustainably extract energy from tidal flows that don't compromise sediment equilibrium. The French haven't pursued the idea of building any more Tidal Power Barrages like the one on the Rance Estuary (just South of the Channel Islands). Why? See above. Canada are not considering another Annapolis scheme and they have numerous potential sites.
Why doesn't the government read the previous studies on tidal energy from the Severn Estuary?
Education, Education, Education