Letter | Published:

Tides at Port Darwin

Nature volume 68, page 295 (30 July 1903) | Download Citation

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Abstract

ALONG the north-west coast of Australia the tidal wave, flowing in from the Indian Ocean, produces at most places a large rise and fall. At Port Darwin the mean spring range is about 24 feet, but the range is sometimes as much as 30 feet. A tide gauge of Lord Kelvin's pattern was set up here by the South Australian Government some few years ago, and good records are available up to 1897, since when it has been dismantled, waiting the building of a new jetty. Captain Inglis, the harbour-master at Port Adelaide, and the writer selected the last good records available for a whole year's tides, the records beginning January 1, 1896, and subjected them to a harmonic analysis, with the results given in the table below. The records show a very marked diurnal inequality, especially at the low waters. In the year examined the greatest difference in height between the two high waters occurred in January and December, and amounted to 4 feet 9 inches. In April, however, there was a difference in height of the two low waters of as much as 10 feet. The analysis shows the existence at Port Darwin of a remarkably large annual tide, the water on this account standing nearly two feet higher at the end of summer than it does at the end of winter. At first sight this seems very remarkable, especially when we find that at Kupang, on the island of Timor, to the north, according to Van der Stok, the solar annual tide has a semi-range of only 2.3 centimetres. The tide appears to be a purely meteorological effect due to the conformation of the harbour and the direction of the prevailing winds. The harbour opens towards the N.W., and, as will be seen from a perusal of the wind charts given in Van der Stok's work, “Wind and Weather, Currents, Tides and Tidal Streams in the East Indian Archipelago,” the winds during the summer blow with great persistency from the N.W., tending to pile the water up in the harbour, while in the winter time the prevailing winds are S.E., with, of course, an opposite effect. This is further assisted by the variations of atmospheric pressure. The average barometer readings exhibit a remarkably regular annual fluctuation, as is shown by the following results. The averages are from readings taken at regular intervals of three hours for twenty years, ending 1901:—

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  1. The University, Adelaide.

    • R. W. CHAPMAN

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https://doi.org/10.1038/068295b0

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