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Joined: Dec 2000
Posts: 144
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Joined: Dec 2000
Posts: 144 |
Poole Harbour:
http://makeashorterlink.com/?E1EA321C
It's a large natural harbour with a very small entrance. I seem to remember back in the mists of time that it's something like the 2nd or 3rd biggest natural harbour in the world.
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Joined: Dec 2000
Posts: 13,803
Carpal Tunnel
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Carpal Tunnel
Joined: Dec 2000
Posts: 13,803 |
Love the map site. On second thought, I'd think that this was a pretty small body of water to have a natural frequency of twice a day. Bean? You're the most likely to have anything intelligent to say on this. Any ideas?
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Joined: Mar 2002
Posts: 1,692
Pooh-Bah
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Pooh-Bah
Joined: Mar 2002
Posts: 1,692 |
Only just looked at this thread, golly gosh it is interesting! I am not a sailor or an expert, but I know that the double tide effect operates in the Solent and in Southampton Water. If you zoom out on the map of Poole Harbour you will see where these features are. I have understood that this occurs because as the water rises for high tide in the English Channel it does so first at the western end of the Channel and then gets progressively later as you move eastward up the Channel, so you get a high tide pushing into the Solent from the west as the tidal effect passes the western arm and then a second body of water from the east as it passes the eastern arm. If this is truly the cause of the double tide, however, I am surprised that it impacts on Poole harbour, and there may some other reason. When I was a very junior Civil Engineer, more years ago than...., I worked on a project to extend the capability of Poole sewage works. Up to that point they were discharging macerated sewage out to sea. If there were double tides.... well it doesn't bear thinking about really does it...  dxb
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Joined: Dec 2000
Posts: 13,803
Carpal Tunnel
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Carpal Tunnel
Joined: Dec 2000
Posts: 13,803 |
it does so first at the western end of the Channel and then gets progressively later as you move eastward
Now I'm confused. I know, I know. I'm often confused.
Shouldn't the tide move from east to west?
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Joined: Mar 2002
Posts: 1,692
Pooh-Bah
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Pooh-Bah
Joined: Mar 2002
Posts: 1,692 |
Dear Faldage,
Well....yeah, I guess you're right, I didn't make a considered choice of direction there, I subconsiously assumed that because the Channel, the North Sea and the Baltic are just a little adjunct off the Atlantic, they would be fed from the European Atlantic coast tide. I am happy to accept that the effect works east to west, but the double tide is still the result - if the reason I was given is correct. I will try and check on which way the tide moves in the Channel - as said I am not an expert, or even knowledgable, on the theory!
dxb
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Joined: Dec 2000
Posts: 13,803
Carpal Tunnel
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Carpal Tunnel
Joined: Dec 2000
Posts: 13,803 |
they would be fed from the European Atlantic coast tide
That's an interesting point. I hadn't thought of that. We already know that local effects can have huge overriding consequences. All this stuff is very impotant to me in my long term goal of unsuccessfully understanding the universe.
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Joined: Aug 2001
Posts: 2,605
Carpal Tunnel
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Carpal Tunnel
Joined: Aug 2001
Posts: 2,605 |
my long term goal of unsuccessfully understanding the universe
A most optimitic goal. It's difficult enough to meet the goal of unsuccessfully understanding the universe.
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Joined: Jan 2001
Posts: 1,156
old hand
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old hand
Joined: Jan 2001
Posts: 1,156 |
OK, sorry to take a while to reply. Some thoughts on tides and resonance: Yes, harbours that are enclosed can have a resonant frequency, and I'm sure that can modify the tidal dynamics. There's a formula to work that out, what I need is the length and width of the harbour. It might be tricky because it's a really funny shape which doesn't even approximate a rectangle. Give me some time on that one. (I don't feel like solving the differential equations again when I know the info is in a book on my desk at the university!) Regarding direction of the tide: Tides are actually very long-wavelength waves known as Kelvin waves. They travel with the coast on their right in the NH (which means on the left in the SH). Looks like this one should be travelling East to West. The best I can do on short notice for St. John's Harbour (which is practically rectangular and I just marked an assignment where the students figured out the period of one of the modes of vibration), much more so than Poole Harbour) is http://makeashorterlink.com/?H2F7213C, if anyone's interested. Here's a much better map, courtesy of the Port Authority: http://www.sjpa.com/images/Facilities/HarMap1.jpg
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Joined: Oct 2000
Posts: 5,400
Carpal Tunnel
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Carpal Tunnel
Joined: Oct 2000
Posts: 5,400 |
Speaking of harbors.. here is a boat trip round NY upper harbor.. the slide show is about 350 slides, it covers about 10 hours.. of a commercial tourist attraction ride around Manhattan island. the url is to a home page, with a live web cam, or click on link to take the virtual tour.http://www.earthcam.com/usa/newyork/circleline/
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Joined: Sep 2001
Posts: 6,296
Carpal Tunnel
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OP
Carpal Tunnel
Joined: Sep 2001
Posts: 6,296 |
Well, this thread is ready to go on out to sea, and I've found a lovely ocean word I don't believe we have here:
spendrift
It's defined in Random House Word Menu:
spray swept by wind from waves during storm at sea...
and then an equally lovely term is given as a synonym:
spoondrift
...I can go to sleep on those two words, stormy though they may be. What do you call a word that sounds as though its one thing (e.g., spendrift and spoondrift sound laidback and easy), but is actually quite something else? Spoondrift just doesn't sound stormy at all to my ear.
Beach regards,
WordWave
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