On Sat, 14 Jul 2012 14:17:37 +0100, geoff wrote:

Tidal power is the next big one.

Ah - silt collectors

Only if you build a barrage. Another possible way to extract power from
the tides are "underwater wind mills". You don't get as much energy but
you don't suffer the silting problems that a barrage does. Lagoons are
another possibilty, you have big sluices on the downstream side that are
normally closed and the water flows out through turbines. When the silt
builds up you open the slucies for a few tidal cycles and flush the
lagoon of silt.

--
Cheers
Dave.