In South Africa, port maintenance dredging is essential. Some ports have rivers running into them. These rivers bring silt into the port which compromises port depth. The movement of ships within a port creates high and low spots due to propulsion wash, where ship propellers cause the sea bed material to move. The effect of Littoral drift or longshore movement of sand occurs primarily on the east coast of the country where the prevailing winds and currents cause a northward movement of sand, so sand flows up the coast. Dredging counters all of these effects, mimicking the natural movement of sand.

Transnet National Ports Authority (TNPA) recently announced that a fixed-jet pump sand bypass system installed at the Eastern Cape port of Ngqura will meet its stringent dredging targets despite a number of significant challenges. The sand bypass system will handle a dredging target of 240 000 tons of sand a year, and this will be achieved largely without the use of a visiting dredger.

The Port of Ngqura nurturing its green status

The Port of Ngqura is the first port in the world to have a fixed jet pump sand bypass system. This computer-controlled sand bypass system consists of jet pumps which mimic the natural longshore drift of sand along the coast. This is achieved by pumping the sand from the up drift (west) section of the coast to the down drift (east) section of the coast.

Sand is captured in a sand trap and pumped via pipelines to a discharge point on the opposite end of the port. Capturing and discharging both occur in the wave zones.

“The system requires a rigid maintenance programme which keeps it going 24 hours a day, seven days a week. The port had to develop and refine maintenance-, standby- and recovery plans in time to counteract the temporary shortfall as part of a continuous improvement process. This included making provision for unplanned maintenance, daily planning and scheduling and improving maintenance techniques - all remaining within budget,” says Freddie Melikhaya, Mechanical Engineering Technician at TNPA.

The Port of Ngqura is the only port in South Africa to have a Record of Decision for its construction and operation. This means that it is the only port that was subjected to environmental legislation during its entire development, operation and any future development.

A number of innovations have been introduced at Ngqura that will gradually find their way into more general port use across older South African ports, TNPA said in a statement. TNPA’s Dredging Services department is implementing an investment programme in excess of R2 billion to renew its fleet. This aids the removal of approximately four million cubic metres of excess material from the seabed every year at South African ports.

Credit: https://www.transnetnationalportsauthority.net/OurPorts/Ngqura/Pages/Overview.aspx


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