Port of Ngqura: Dredging and excavation of temporary bund

The dredging works were part of the final works required to commission Container Berths D102 and D103.

The management of the dredging works was expected to be challenging, both technically and contractually, since dredging had to take place adjacent to existing structures, and concurrently with other contracts. PRDW, as designer of the dredging works, was appointed to the owner, Transnet, to provide expertise to the EPCM team to help manage these works.

The dredging was carried out by China Harbour Engineering Co. Ltd. The total dredging volume was approximately 1,300,000m3 . Material varied between fill material, marine deposits, gravels and cobbles and soft to medium hard cretaceous rock.

Dredging began using a backhoe dredge, the Jin Tai. The Jin Tai was later replaced by two grab dredges, the To Sho fitted with a 106m3 grab, and the Jin Jian fitted with a 18m3 grab as well as a rock chisel.   

Special care was taken to mitigate the risk of damage to existing structures (i.e. quay wall and revetment). Method statements were rigorously reviewed and work had to be carefully monitored.

Bathymetric surveys were carried out on a regular basis. These consisted mostly of single beam surveys. A number of high resolution multibeam surveys were also carried out to investigate specific underwater objects and structures, and to verify compliance with specified depth requirements.