Tidal barrages are a proven technology. The famous barrage at La Rance in France, where the tidal range is a whopping 8 metres on average, has produced an average power of 60 MW since 1966. The tidal range in the Severn Estuary is also unusually large. At Cardiff the range is 11.3m at spring tides, and 5.8 m at neaps. If a barrage were put across the mouth of the Severn Estuary (from Weston-super-Mare to Cardiff), it would make a 500 km2 tide-pool (figure 14.8). Notice how much bigger this pool is than the estuary at La Rance. What power could this tide-pool deliver, if we let the water in and out at the ideal times, generating on both the flood and the ebb? According to the theoretical numbers from table 14.4, when the range is 11.3 m, the average power contributed by the barrage (at 30 W/m2) would be at most 14.5 GW, or 5.8kWh/d per person. When the range is 5.8 m, the average power contributed by the barrage (at 8 W/m2) would be at most 3.9 GW, or 1.6kWh/d per person. These numbers assume that the water is let in in a single pulse at the peak of high tide, and let out in a single pulse at low tide. In practice, the in-flow and out-flow would be spread over a few hours, which would reduce the power delivered a little.
o Bristol o Weston-super-Mare o Bristol o Weston-super-Mare
The current proposals for the barrage will generate power in one direction only. This reduces the power delivered by another 50%. The engineers' reports on the proposed Severn barrage say that, generating on the ebb alone, it would contribute 0.8 kWh/d per person on average. The barrage would also provide protection from flooding valued at about £120M per year.
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Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.