A "barrage" is essentially a large dam which is composed of tunnels which water flows through during the changing of the tides. A barrage is constructed across a river estuary.
The turbine can be activated by either the direct flow of the tides, or by the tidal flow pushing air through a pipe which triggers the turbine (Darvill, 2006).
Darvill's Page
These turbines would be more cost-efficient to build and would cause less environmental problems than the typical tidal barrage system.
BBC News
Blue Energy, Inc. is based in Canada. The company produces these turbines which rely on rapidly-flowing tidal currents. It is a predictable method in the sense that the energy that it can collect from powerful narrow and short constrictions relies on the lunar orbit (Blue Energy, 2006). This energy generation method does not depend upon weather or climate.
Blue Energy
Extracted from www.darvill.clara.net/altenerg/tidal.htm
* It produces no greenhouse gases or other waste.
* It needs no fuel.
* It produces electricity reliably.
* Not expensive to maintain.
* Tides are totally predictable.
* Offshore turbines and vertical-axis turbines are not ruinously expensive to build and do not have a large environmental impact.