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Old 23-03-2014, 15:44   #16
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Re: Interesting high/low tide pics

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Originally Posted by CaptTom View Post
Right. Which is why I asked. I know some isolated locations around the world have oddball tides due to geography and bathymetry. But 8 hours is closer to 1/3 of a lunar day, so I fail to grasp how you'd get consistently high and low water 8 hours apart. I assume it's a mistake, but I stand ready to be educated.
I suspect that you are correct and the writer was mistaken but...

Variations in wind, local currents and amount of tidal stream (think increased flow down the rivers and into the estuaries after rains) can mess with the timing a bit and there is period around high and low tide when, as the flow slows/stops/reverses, the difference is slight. We used to call it dwell but I've no idea if that is correct terminology or local idiosyncrasy. So I doubt the exact timing was critical and, in some cases when the factors align, the visual difference between six and eight hours apart might not be as great as you might think. Obviously this varies from place to place and time to time.

But I would still guess that they corresponded to about a normal cycle, assuming that they were even taken on the same day.
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Old 23-03-2014, 16:20   #17
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Re: Interesting high/low tide pics

OK, so my curiosity got the better of me.

Quote from the photographer, "The time between high and low tide averages 6 hours 20 minutes, but this is just an average. In some places the tide may take 8 or 9 hours to come in, but only 3 or 4 hours to go out again; or vice versa; or anywhere in between. And even where the timing of the tides is close to the average, it will change from day to day: so today it may take 6 hours 17 minutes for the tide to rise in the pretty harbour of St Ives, in Cornwall, tomorrow 6 hours 30 minutes, and the day after 6 hours 8 minutes."

Here is an article he wrote and pictures that have a notation showing the time taken. Take a look at the pictures of Wivenhoe, a place I know well, and where I guarantee you can barely see any difference between an hour before and an hour after low tide. If you are ever nearby, grab a pint from the Rose & Crown, go sit on the quay and watch the water rise and fall - you'll easily see what I mean :-)
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Old 23-03-2014, 16:57   #18
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Re: Interesting high/low tide pics

OK, thanks, that makes more sense. The photographer knows what he is talking about, so it looks like someone made a typo on the web page.

Obviously if there is the flow of a river or some other similar factor involved, the ebb will exceed the flood in duration, but that's an isolated case. Also, places with grossly uneven ebb & flood tend not to have the kind of range we see in the photos. To allow all that water to go out, and come back again on a regular basis, both durations will tend to be roughly equal. Again, not down to the minute, or even half-hour. But roughly 6 or 12 hours apart.

And I agree that an hour before low and an hour after high (roughly 8 hours) will look almost the same as hitting it right on time. The "rule of twelfths," although an over-simplification, would suggest that the tide has only risen or fallen one-twelfth of the way in that hour.
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Old 23-03-2014, 17:38   #19
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Re: Interesting high/low tide pics

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Obviously if there is the flow of a river or some other similar factor involved, the ebb will exceed the flood in duration, but that's an isolated case.
Sorry but I have to disagree with you on this. I don't think it is an isolated case around the British coast, especially on the East coast where I used to live. Lots of rivers that flow into tidal estuaries - I could reach five within 45 minutes from my house, and lots of rain. Now take a day where the wind is blowing off the land (in the same dirrection as the ebb) and there have been a few wet days, so lots of water flowing from the rivers to the estuary - and the tide will rush out and craw back in.

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Also, places with grossly uneven ebb & flood tend not to have the kind of range we see in the photos.
I think I disagree here as well. I don't see a connection between range and uneven ebb/flow. I'm not convinced but I'm no expert, so I would certainly be interested in any contrary opinions. As well as the range, in some places around the U.K., the land falls away very slowly and the tide goes out a long way.

It's all what you get used to - I was amazed when I moved to California and you could just go sailing anytime you liked, without worrying if there would be enough water to get out or back.
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