The battle of the sandbar at Durban harbour

The greatest obstacle that has always challenged the successful use of the natural lagoon that is today Durban’s harbour is the containment of a massive sandbar, which, left unchecked, has the natural inclination to block the entrance to the port facility between what is known as the Bluff and the Point. In fact, this challenge flared up again as recently as last year, when a few massive container vessels calling at Southern Africa’s busiest port reportedly touched the seabed while navigating the entrance and harbour channels.

In its natural state, the sandbar has the ability to accumulate to a significant height, leaving an average depth of just 6 ft of water to pass over it at low spring tides. It is essentially caused by the collision of two opposing currents: the littoral drift, which moves sand northwards along the East African coastline is forced to curl around the toe of the Bluff peninsula by the south-flowing Mozambique current. This collision of currents causes vast tonnages of sand – some estimate up to one-million tons a year – to be deposited in the channel entrance.

Such has been its significance that the history of Durban’s harbour is largely the story of man’s battle to tame this unrelenting force of nature. In fact, the initial attempt to shift that sandbar can be regarded as the first major civil engineering project undertaken in KwaZulu-Natal.

It had always been fully realised that Port Natal, which was the harbour’s original colonial name, had the potential to become a jewel in the crown of any maritime empire. All that stood in the way was the notorious sandbar. So, following the formal annexation of the district of Natal as a British colony in May 1843, many a mariner and settler expended considerable energy pitting their wits against the might of the shifting sand. By the end of the decade, little had been done to conquer the bar – large vessels were still compelled to anchor alongside the Bluff, while lighters were used to convey passengers and goods over the bar and into the lagoon – and the colonials realised that what was needed was, in fact, a qualified harbour master with extensive civil engineering experience. They found just the man for the job in John Milne, who bears the honour as Port Natal’s first harbour engineer. Born in Kincardine, on the Firth of Forth, Scotland, in 1802, Milne was a seasoned civil engineer, having worked on various harbour projects in Scotland, England and Ireland.

Milne arrived at Port Natal in December 1849 and immediately set to work, surveying his new task. Having fully surveyed the harbour and its mouth, he realised that he had two basic choices in removing the bar: dredge the sand away or alter the configuration of the mouth to allow nature’s forces to do that job.

While the ancient art of dredging had progressed somewhat by 1850, nowhere in the world had a system been developed that allowed dredging to be undertaken in exposed conditions. Thus, Milne’s only viable option was to harness the ebb flow of the lagoon water to promote greater tidal scour of the bar.

The proposal he presented was to build two breakwaters converging to within 500 ft at the channel entrance and, by so doing, increase the velocity of the ebb tide, as it squeezed out between the pier heads. He further argued that, as the only force that could return the ebb’s sand load was the force of waves breaking on the shallow bar, the breakwaters needed to be built out into deeper water, beyond the bar and breaking waves, so that the ebb tide would have no opposition. The estimated cost of that ambitious project was £77 743 (which, today, would be in the region of R166-million).

His proposal was approved by the Harbour Committee and Milne started working on the first phase of the project – the construction of the North Pier and breakwater, at a cost of £22 866 – towards the end of 1852.

Milne’s first priority was to find a source of stone with which to construct the breakwater. After fairly little deliberation, it was decided to use sandstone quarried from the Bluff, opposite the Point. By the end of 1854, some 22 000 t of sandstone had been quarried and used for the North Pier. By this time, Milne claimed that a water depth of 5 m over the bar had already been achieved.

However, at this point, work came to a virtual standstill when it was decided to move the quarry to the end of the Bluff. However, in order to convey that rock to the desired point, it was necessary to construct a short tramway system, so the harbour works were put on hold until that could be completed. (The story of this railway track, the first in Southern Africa, will be elaborated upon in the next instalment.) Following its completion in February 1856, work on the North Pier restarted.

Unfortunately, following yet another shipwreck on the sandbar, this time of the Annabella, Natal’s new lieutenant governor, John Scott, ordered all work to be stopped. He also ordered an inquiry into Milne’s project in April 1857. The findings of that inquiry were never published but there were certainly acrimonious differences of opinion between Milne and the rest of the Harbour Committee, for he resigned shortly thereafter. By the time he resigned, only 135 m of the North Pier had been completed, at a cost of £14 000. Despite his best theories and efforts, Milne was ultimately conquered by the mighty sandbar and the mantle of freeing Port Natal would have to be taken up by a new generation of civil engineers.