Mulberry Harbour and Tidal Range at Arromanches

 Big ships are so deep that they can't get close to a beach without getting their bottoms stuck in the sand. This caused a problem after D-Day. The solution was to build a deep water harbour. Another problem is that the depth of the water changes twice a day due to the tides. The tidal range in the English Channel is particularly high. I have posted about the tides on Guernsey before. The reason seems to be to do with the geometry of the channel. There are some places on Earth where the tidal range is almost zero. I need to find out where and go! If you build a fixed pier then ships that dock against it will be at the right level at some times of the day and far too low down at other times. So at Arromanches, the revolutionary design was to put some big poles (called piles) into the seabed and to clip the pier around them. The pier wasn't completely fixed - it was free to go up and down with the tides.

 These days the design is used for yacht piers. This one is at Baie d'Orne, looking towards Ouistreham ferry terminal. Looking at the height of the poles, the tidal range must be up to 4 metres.