Environmental Engineering Reference
In-Depth Information
grind corn. But, despite this historical pedigree, there are today only four
sizeable, working tidal barrages in the world, all built in the last fifty years
and none of them (yet) in the UK.
The biggest is the barrage that the French built over the Rance river
in Brittany in the 1960s. Three smaller ones exist at Kislaya Guba on the
Kola peninsula in Russia, at Jiangxia in China and at Annapolis Royal in
Canada's Nova Scotia province. Apart from the latter, all of them operate
in both directions, generating electricity from both the incoming and
outgoing tides passing through the barrage.
The Annapolis Royal barrage, like the ancient Woodbridge one, oper-
ates in only one direction, trapping incoming water and releasing it to
generate power when the tide has gone out. This Canadian barrage is, in
fact, the best placed of all, being situated on an inlet of the huge Bay of
Fundy, which has the world's highest tide differential - seventeen metres
(between high and low tide). This long (270 km) bay between Nova Scotia
and New Brunswick is ideally shaped to produce record high and low
tides because, as it extends east, it grows narrower as well as shallower.
The main objection to tidal barrages is the same as to hydroelectric
dams on the non-tidal parts of rivers around the world - the ecological
impact on animals, plants and soils. These environmental issues will play
a big part in the UK debate about whether to build a barrage across the
Severn estuary at the top of the Bristol Channel. It has the same combina-
tion of diminishing width and depth, and thus produces tides almost as
dramatic as the Bay of Fundy. A possible sixteen-kilometre barrage across
the Severn could generate as much as five percent of the UK's electricity,
at a cost of some £15bn, but also at the price of disrupting rich fish and
bird-breeding areas.
Tidal stream
Placing turbines into fast-flowing currents or tidal streams is a far more
recent idea. It could also be taken up more quickly, because it does not
have the environmental drawbacks of barrages. The Marine Current
Turbines company has placed a tidal power turbine in Strangford Lough
on the coast of Northern Ireland, and MCT is working with RWE, a
German-owned utility company on a project off North Wales.
Another company, Lunar Energy, is planning to install turbines off the
Pembrokeshire coast with Eon. And OpenHydro, an Irish company, has
one of its tidal turbines hooked up to the UK grid at the European Marine
Energy Centre in Orkney.
