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During the summer of 2002 I was driving along the coast of Norway, and while pondering a lot of different items - one item struck me: Why is the local tidal variation in the south-east of Norway only a couple of feet, while at the extreme North of Norway the variation is a couple of meters ?

Putting on my research hat, I began looking into what effects could cause this. Eliminating a lot of different factors that does not have any local influence, it finally came down to one factor : Denmark and Old Blighty (Or in professional jargon: a large obstruction to the free flow of a fluid).

In open oceans the effect of the tides is minimal (only a few feet) and it's only when the tidal crest encounters shallow water or land that the effect becomes notable. Fluid mechanics applied to the water gets us the following facts:

  • It is not free flowing, but possesses a bit of viscosity so that the movement is somewhat dampened.
  • The tidal crest slows down when it encounter the shallow water of the North Sea due to the friction of the seabed, and also due to hydraulics (maximum wave speed goes down when the water height goes down).
  • Continents stop the tidal wave, and creates a barrier.

These effects cause a resonance at the coast, so that local variation at the coast is higher than that of the ocean {2}.

For south-eastern Norway, the effect of Denmark dampens the movement of water, so that by the time the water has begun to move, it is time for a new cycle to begin - effectively cancelling out most of the tidal variation. This is also shown in the Baltic sea {4}, where the tidal variation is insignificant next to the variation we have in the north of Norway. This is also because the water has to pass through the small straight between Sweden and Denmark.

The following sources made me believe I was right:
{1} http://www.math.uio.no/~bjorng/tidevannsmodeller/tidemod.html
{2} http://www.co-ops.nos.noaa.gov/restles1.html
{3} http://www.dnmi.no/cgi-bin/vannstand-applet.cgi
{4} http://www.smhi.se/weather/havsvst/havsvst_tab.htm

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