g'Day Irene and others.
Tidal movement in some areas are not quite as straight forward as the
theoretical model suggests. Now some might argue this subject is off
topic. But if one relates tidal movement to wader watching along the
Kimberley coast and then considers what might happen to the observer if
a 8 m. tide comes in when you expect it to ebb, it may still be worth
reading about tides, that is unless one is a strong swimmer or prefers
to hunt crocodiles rather than birds.
At Cape Londonderry, the most northern point of mainland Western
Australia, when the tide is near high on the eastern side of the Cape,
only 25 km to the west at Cape Talbot, it is near low tide. The actual
difference is about 4 hours and this tidal variation in such close
proximity generates notoriously strong currents and rough seas around
this Cape, especially when wind is blowing against the tide. (compare
tide tables for Leseuer Island with Geranium Harbour)
When flying over Cape Londonderry at spring tide peaks, this phenomenon
is easily observed. Large areas of exposed sand flats are visible
around the Drysdale River estuary near low tide when, in the same field
of vision, water on the west side of the Cape can be seen lapping the
high water line on the sandstone rocks
Another example of opposite tides occurring simultaneously within the
same region is found either side of the Joseph Bonaparte Gulf; comparing
Darwin @ S 12.28', E 130.51' (Time Zone -09.30 within Timor sea
influence) with Cape Voltaire (Krait Bay) @ S 14.15', E 125.36' (Time
Zone -08.00 within Indian Ocean influence).
Why do we observe two opposite tides in the same region, when the model
suggests that gravitational and centrifugal influences on tidal movement
in any region should be uniform and result in mainly two bulges of water
being high tides that follow the moon across the surface of our planet.
Regards
Ian May
PO Box 666
Enfield Plaza SA 5085
Tel: (08) 8380 9553
Mob: 0409 474 575
Birding-Aus is on the Web at
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