Monday, 3 March 2014

Waratah - the sandbar at Durban Port.

Access to the port at Durban was hampered by a sandbar, the result of opposing currents - south flowing Mozambique Current and littoral drift moving sand northward along the East African coast.
It is this littoral drift that curls around the end of the Bluff at Durban port, dumping vast quantities of sand across the channel.

In the mid 1800's emigrant ships had to discharge passengers and cargo at the outer anchorage due to the sandbar. The first to tackle the problem was an engineer, John Milne who arrived from Scotland in 1849.  He believed that tidal scour would solve the problem. Water flowing into the port from the rivers exceeded that of the tides flowing in (with the sand). He instigated the building of two piers to narrow the width of the mouth and in so doing increase the speed of the out flowing water, hence scour.

But it was only by 1881 that real progress was made with the construction of the piers under the guidance of Edward Arthur Innes, harbour engineer. Ironically a dredger was acquired to assist with construction rather than dredging the sandbar itself. Innes died in 1887 having made great progress on the northern and southern piers

By 1888, another Scot, Cathcart Methven was appointed harbour engineer. This time tidal scour in conjunction with dredging was employed to deal with the problem of the sandbar.

Charles Crofts took up the reigns in 1895 as harbour engineer and pushed forward with the development of dredgers. Dredging eventually conquered the problem of the sandbar by 1904 and the 12 967 ton Armadale Castle was able to enter Durban Port.

Tonnage entering the port increased from 319 878 in 1895 to 2 542 130 by 1907. In 1895 the average depth of the sandbar was 12 1 in. By 1907 this had increased to 32 ft 8 in.  The draught of the deepest vessel in 1907 was 30 ft 7 in. The fully laden Waratah departing Durban 26 July, 1909, had a draught of 28 ft. 9 inches. Assuming that 32 ft 8 in. still applied in 1909, and taking into consideration tidal and seasonal variations, the Waratah probably cleared the sandbar without incident.

Newspapers of the time often reported vessels scraped the sandbar 'lightly'. This was not considered a threat to the seaworthiness of vessels. However, the Koombana illustrates the vulnerability of steel hulls of the time and the inaccuracy of declaring 'no damage sustained' after an episode of grounding.
If vessels were sound I believe a 'light' scrape of the sandbar would not cause major damage to hulls.
However, as in the case of the Koombana, if there was pre-existing damage, particularly inadequately assessed and repaired, 'light' scraping could tip the balance of hull integrity.

entrance to Durban Harbour

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