Channel Design & Dredge/Disposal

Channel Design

The channel design report carried out by Royal HaskoningDHV considers several options for redesigning the Whangarei Harbour shipping channel.

The redesign includes deepening and realigning the existing navigation channel to enable access by fully loaded Suezmax crude oil tankers.

The report draws on a range of detailed investigations. These include:

  • Assessment of channel design options based on international best practice guidelines;
  • Identification of ecologically sensitive or important landscape or natural character areas which should be avoided where possible;
  • Liaison with relevant parties such as the Harbourmaster, Northport, North Tugz and Refining NZ to identify navigational and operational priorities;
  • Several rounds of simulations to test channel design options under a range of operational conditions and potential scenarios.

Channel Design Findings

Together with relevant stakeholders, including the Harbourmaster, Northport and North Tugz, we have come up with a preferred option for the new channel design.

This option will involve some dredging to deepen the channel, some re-alignment to straighten the approach to the harbour and some re-positioning of aids to navigational such as channel marker buoys.

In choosing this option, a number of different designs were considered and assessed with the help of experts. Simulation testing was carried out that took into account a range of possible operating conditions such as arrivals and departures, different weather conditions and night vs. daytime sailing.

Taking these steps allowed us to choose a preferred option that ticks all the right boxes:

  • Safest and simplest to navigate – a big improvement for ship pilots and risk reduction ✔
  • Avoids impacting ecologically sensitive, important landscape or natural character areas ✔
  • In line with international best practise ✔

If you’d like to know more of the nuts and bolts of the effects these are outlined in the summary document here.

You can read further detail in the related downloads section below.

Dredge and Disposal

The report prepared by Tonkin & Taylor summarises key aspects on the dredging and disposal methodologies required for the refinery’s proposal. This report supports the Assessment of Environmental Effects and is part of a suite of technical reports assessing the actual and potential effects of the applications.

Capital and maintenance dredging material and volumes

  • Main areas for dredging are the outer channel and the berth area at the Refinery. There will be targeted dredging in other areas.
  • Dredging is within the fine to medium sand layers of the shipping channel.
  • The expected dredge volume is 3.7 million cubic metres (m3) over 1.95 km2.
  • Low sedimentation within dredge areas of the channel means that targeted maintenance dredging could be required every 2 to 20 years to maintain navigable depth.
  • Maintenance dredging will be placed in either of the marine disposal areas, or be used for beneficial land based disposal.

Dredge and Disposal Findings

The proposed channel design will require some harbour dredging and disposal. We have been busy working with our independent experts to come up with the best possible plan for this.

What are the key things you need to know?

  • Capital (initial) and maintenance (ongoing) dredging will be carried out
  • Capital dredging may take up to six months and involve an estimated volume of 3.7 million cubic metres of sand
  • Maintenance dredging may be required every 2-5 years in some areas
  • Dredging will likely be carried out using a small-medium sized trailing suction hopper dredge, possibly assisted by a backhoe dredger and barge. A cutter suction dredge may be used for localised dredging
  • Two marine disposal areas have been chosen, and it is possible some sand will be disposed of on land
  • The marine disposal areas have been carefully selected to avoid adverse effects on the environment (including ecology and tides, waves and currents)

If you’d like to know more of the nuts and bolts of the effects these are outlined in the summary document here.

You can read further detail in the related downloads section below.

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