After a power-generating phase that runs around five hours, the level of the head pond has generally dropped to within 1.6 metres of the incoming tide, so the wicket gates shut to start the next cycle. The tides follow a 12.5-hour ritual, occurring roughly an hour later each day.
How the Straflo turbine works
The Straflo turbine turning at the heart of the Annapolis Tidal Generating Station ( see illustration below left ) generates electricity only when the flow of water is out to sea.
7 January 2010 23:00 GMT
Updated
25 November 2012 11:12 GMT