The Deeper Story

Two main areas would be dredged – the majority (80%) in the outer shipping channel, with the remainder around the refinery jetties and turning basin (where ships turn as they depart). These two areas are shown on a map here. Some smaller-scale dredging may be required in other parts of the channel.

The depth will depend on the location. We expect to dredge up to four metres in the outer and inner shipping channels, and up to eight metres in targeted spots around the refinery jetties. The depth of dredging is shown on a map here

It’s expected that around 3.7 million cubic metres (m3) of sand would be dredged. To put that in context with dredging plans at other New Zealand ports, Port of Tauranga has consent for 15 million m3, and Port Otago for 7.2 million m3.

We expect the dredging to take up to six months to complete. Exactly how long will depend on the size of the dredge that is used.

Most of the dredged material would be relocated to the seabed at a depth of 45 metres south east of Whangarei Harbour. Some of the dredged material would be deposited closer to shore, at depths of up to 15 metres, to replenish sand that has been lost from the ebb tide delta.

Some could be deposited onshore to replenish beach sand or for reclamation. We are currently working through options for land disposal.

The seabed sites have been chosen because of a number of economic and environmental considerations – including impact on the seafloor, matching of sediments with those to be dredged, and in order to minimise any impact on flora and fauna (birds and marine life).

For the majority of the dredging it’s likely that a small to medium Trailing Suction Hopper Dredger would be used. For dredging at the refinery jetty it’s likely that a Backhoe Dredger would be used.

If approved, dredging works could be underway in 2019 at the earliest.

A small amount of maintenance dredging is expected, particularly in the first few years as the slopes on the sides of the channel settle.

All ship movements (crude and otherwise) are governed by a range of port and harbour safety requirements which are the responsibility of Northland Regional Council, the Harbourmaster, Northport and Maritime NZ.

Every crude ship must have a minimum safe clearance underneath its keel be approved to enter the harbour. At Whangarei, a Dynamic Under Keel Clearance system gathers up-to-the-minute information on wave and weather conditions on the harbour to determine whether it is safe for a ship to enter.

As part of the resource consent process, Refining NZ has commissioned an independent navigation risk assessment, which shows that the new channel design improves safety for crude ships accessing the refinery.

No, Suezmax vessels already visit the refinery. However, those vessels currently arrive slightly under-loaded. This proposal is intended to allow those vessels to bring full loads of crude oil.

No – there will be fewer crude ships overall. The refinery will receive the same amount of crude oil for processing, it will just arrive at Marsden point in bigger sized “parcels”.

The overall risk is significantly reduced by improving the channel alignment and by fewer ship movements overall.

There are measures in place to prevent a major spill occurring in the first place.

Crude ship operators are required to follow stringent safety standards. Ships are double hulled for extra protection, and the cargo is held in compartments so that damage in one part of the hull does not impact the full load.

Hoses and pipes for transporting crude are regularly maintained and tested, and have emergency shut-off valves to stop crude being discharged at the refinery’s jetty.

In the event of a harbour spill the refinery marine team has access to oil recovery and containment equipment and is able to respond quickly. Backup is provided by the refinery’s emergency services team, trained refinery volunteers and where required, the Northland Regional Council oil response team. Maritime NZ would provide further support in a major spill.

Our oil spill response is tested by regular exercises with the Northland Regional Council and Maritime NZ oil response teams.

The refinery is aware of these areas of special interest and for that reason is proposing a channel design option that avoids impacting ecologically sensitive, important landscape or natural character areas.

Extensive field work and hydrodynamic modelling by the independent experts has concluded that the proposed changes will have very little effect on existing coastal processes (waves and tides), and around Mair Bank and in the ebb tide shoal, no discernible effects are expected.

In addition we are proposing real time monitoring to ensure there is no impact on key rocky shore habitats, including the marine reserve and Home Point.

The refinery is proposing a series of measures to mitigate any potential effects. Measures include:

• Choosing a disposal site for some of the dredged sand that helps prevent future erosion of Mair Bank;
• Monitoring any potential changes including via an annual survey of the channel, Mair Bank and the wider ebb tide shoal, before and after dredging;
• Monitoring water turbidity against acceptable limits and responding where necessary, for example, with operational controls on dredging and disposal; and
• During transportation of dredge material valves on the dredge will remain closed to prevent spillage outside designated dredge and disposal areas.

There are two alternatives:

• Single Point Mooring, where crude ships berth at a mooring point outside of the harbour and crude is transported by underwater pipeline to the refinery. This would be a major project in itself, and likely have a greater impact on the harbour environment.
• Ship to ship transfer in deep water to transfer the cargo into smaller tankers for final discharge at the refinery.

Either option would require the use of a VLCC (Very Large Crude Carrier) which carries twice the cargo of a fully loaded Suezmax – and would require much more storage capacity at the refinery.

An assessment of alternatives has been carried out as part of a series of expert studies and can be found here.