http://www.pla.co.uk/films.cfm
Look at the bottom for the vid - called time and tide.
The tidal range on the river section of the tidal Thames varies between 5 metres and 7 metres - that is the difference in the height between low and high water. The tidal range is dependent on whether the tide is on neap or spring tide cycle. This has a number of impacts including when vessels can move on the river (bigger vessels need the deeper water of high tide) and the type of structures (bridges and piers) needed for getting passengers on and off boats on the river.