Rock removed from shipping lane

Ports of Auckland’s shipping lane deepening project in the Rangitoto Channel has reached a successful milestone. All the hard rock has been mechanically excavated and no blasting has been necessary.

The hard rock area (near North Head and the western side of Rangitoto Island) has been successfully removed using a barge-mounted backhoe dredger. This initial dredging operation specifically targeted all of the harder Parnell grit rock found in the commercial shipping lane.

“Ports of Auckland was committed from the beginning to using alternatives to blasting if at all possible for both environmental and cost reasons,” says Ports of Auckland General Manager Port Infrastructure Ben Chrystall.

“We went to a lot of effort to bring in specialised equipment and we have achieved a very good result,” he says.

The research-based, environmental watchdog group Friends of the Earth is pleased with the successful outcome.

“Friends of the Earth is pleased to see that an alternative method to blasting has been so successful. It has always been our objective to ensure that the rock removal would not cause possible injurious effects to marine mammals,” says Friends of the Earth Co-Director Bob Tait.

This special dredging operation was carried out early and separately from the main dredging works as the result of an agreement between Ports of Auckland and Friends of the Earth. The agreement included additional resource consent conditions for the shipping lane deepening project.

The two parties had also agreed to additional marine mammal protection measures in the unlikely event that blasting was required. These measures were in addition to a suite of marine mammal protection measures developed by Ports of Auckland in conjunction with Auckland Regional Council, DoC, Iwi and other parties.

“The marine mammal protection measures developed have established a benchmark for best modern practice,” says Mr Chrystall.

For more details on the measures please refer to the Ports of Auckland website www.poal.co.nz/about/portdevelopmentchannel.htm

Ports of Auckland contractors Heron Construction Limited carried out the fragmentation and removal of the Parnell grit rock.

The main dredging works are scheduled to begin in this calendar year and continue for one to two years in patches along a 7,400-metre strip from North Head to the southern end of Rangitoto Island.

All dredgings from the shipping lane deepening project are being used to form mudcrete, an environmentally friendly fill, for the Axis Fergusson container terminal reclamation.

The Axis Fergusson container terminal is being extended to cater to future increases in port throughput. The terminal extension building timeline is carefully matched to predicted increases in container volumes. This is to ensure there is always sufficient container handling space in Ports of Auckland’s container terminals. (Please refer to media backgrounder for more information.)

The quantity of shipping lane dredgings has been reduced from 1 million to approximately 500,000 cubic metres. This is to leave room in the Axis Fergusson reclamation for future recycling of maintenance dredgings. The shipping lane dredged depth will be 12.5 metres, a significant increase from the current 11.2 metres.

Purpose of deepening the shipping lane

Ports of Auckland is deepening the commercial shipping lane to widen the tidal window to better handle the new larger containerships.

Ports of Auckland received resource consents to dredge the commercial shipping lane in April 2002 after a comprehensive public consultation process.

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