The vertical difference between high and low tide ranges greatly, from nothing, to a few feet in open ocean, to 30 - 40 feet in some locations, including along the English Channel.
Why?
It does not seem to be an exclusive issue of latitude … so what is it?
It depends largely on the conformation of the coast. Here in Panama, we get tides of up to 18 feet on the Pacific side in the semi-enclosed Gulf of Panama. Only 50 miles away on the Caribbean coast, which is more open, the tides are only about 2 feet.
So it is a funnel effect?
I believe that has a lot to do with it. The highest tides are in the Bay of Fundy, which narrows very strongly along its length.
This NOAA page linked to in the Wiki article gives more info:
Thank you.
I’m heading for the Bay of Fundy in a couple of weeks. We’re going to ride the “tidal bore” a wave that forms as the incoming tide opposes the out flowing river. Apparently, it can get pretty rough as the bore crosses sand bars and such. Looks like fun in a Zodiac.
Wear a flotation device. I’ve seen that on TV and it looks pretty scary.
I don’t think I’ve ever seen a 8’ high tide here in Southern California. When I was in Southeast Alaska, their high tides were over 20’!
I suspect that you can get resonance issues, too, if a particular bay just happens to have a resonant frequency of 2/day for standing waves.
We spent some time on the Bay of Fundy on our honeymoon, although I couldn’t get my bride to try rafting on the tidal bore. The tides are amazing, though - you can walk along the wharf at Digby and the boats are all up next to the docks, and then 12 hours later come back and they are literally sitting in the mud on the floor of the harbor eighteen feet below. Here’s a picture, although it looks like the image on the left is not full high tide.
Like Chronos suspects, tides much larger than open ocean tides result from resonance, as I read. That is, it’s not so much a funnel as it is a figurative bathtub whose sloshing frequency is close to the frequency of the tides. It helps if the bathtub is also shaped to not dissipate sloshing, or in other words to resonate with a high Q. I think if you could dig a long channel that ran east to west, whose bottom profile in the east-west direction was a chord of a circle, and whose walls were straight and parallel and smooth, and you made its length right to resonate at 6 hours (or whatever the tidal frequency is), you’d maximize the tide.
