Dredging
Dredging is required in most ports because of sediment movement and run-off from surrounding land areas and city streets. It ensures that ships can navigate and berth safely.
A small, barge-mounted dredger conducts maintenance dredging around the Bledisloe container terminal.
The Waitemata Harbour has reasonably strong tidal movements, which reduces the build-up of sediment in the channel.
Some siltation in the Port basin comes from the run-off from stormwater outlets from surrounding city catchments. The Auckland City Council is working to upgrade the city stormwater system, which will help to reduce siltation and impact on water quality in the harbour.
Ports of Auckland carries out a programme of regular maintenance dredging around its wharves to keep berths at notified depths.
Dredgings currently are disposed of in the reclamation area at the north-east corner of Fergusson container terminal. The dredgings are mixed with cement to make mudcrete for the reclamation. This is both cost effective and environmentally friendly.
Because the mudcreting quickly binds dredged sediment into a solid mass, there is very little impact on the harbour or the water quality. The dredged material is predominantly marine mud. Extensive monitoring has found no problems with contamination or biotoxicity.
The Manukau Harbour, on Auckland’s west coast, is a tidal harbour and the Port of Onehunga depends for its operational viability on the ability to dredge between 5,000 and 10,000 cubic metres of sediment a year from the area where ships manoeuvre and berth. Following feedback from recreational fishers of the Manukau Harbour, dredgings from Onehunga are also disposed of in the Fergusson reclamation.
