Preparing for the future

Container ships have doubled in size over the last 10 years and the trend toward bigger ships continues. We are enlarging the existing shipping channel to provide access to larger ships and support Lyttelton’s future as the South Island’s major international trade gateway.

The Fairway commenced dredging the channel on the 29th of August. She is anticipated to complete the work in approximately 12 weeks.

How much bigger?

After all stages of dredging are complete the channel will allow all-tide access for ships with a 14.5m draught. This represents an increase of up to 3000 more containers per vessel – or 144 million more bananas per ship!

How it works

Channel dredging

Channel dredging is done with what’s called a “Trailer Suction Hopper Dredge”. This essentially works like a vacuum cleaner, sucking up sediment from the seafloor into the hopper of the dredge vessel. Once the hopper is full, the dredge vessel travels to the offshore spoil disposal site and evenly distributes the sediment across the site.

Environmental effects

Water quality

The most obvious environmental change people will notice are sediment plumes behind the dredge vessel. These will look like a trail of cloudy patches in the water behind the dredge. The environmental effects of the plumes were evaluated during the consent process. It was found any environmental effects would be minimal and short term as the ecosystem is used to naturally occurring fluctuations in water clarity.

Our instruments continuously measure the amount of sediment in the water to ensure it remains within acceptable levels set by the consent.

Monitoring programme

Our environmental monitoring programme is the most extensive ever undertaken for a dredge project in New Zealand. We are continuously assessing a wide range of environmental factors and adapting dredging operations in response, to ensure environmental effects are minimised.

Fish and marine mammals

Small seafloor organisms tend to have short lifecycles and can recolonise quickly after disturbance. Interestingly, dolphins may even take advantage of the sediment plumes, using their sonar to hunt for fish ‘under cover’. The dredge vessel will have designated marine mammal observers onboard. Their job is to ensure the dredge avoids marine mammals, and will also record the mammals they see and their behaviour to aid wider research.

Beach and shore

Shorelines are being regularly monitored for any changes to sandy and rocky beach environments. We are also monitoring the marine ecology in the harbour and along the coastlines.

Dredging and disposal areas

In the first stage the existing shipping channel is being lengthened by approximately 2.5 km, widened by 20 metres and deepened by up to 2 metres. The dredged sediment will be relocated to a designated 2.5 x 5 km spoil ground located approximately 5 km off Godley Head.

Realtime Monitoring

Key Facts

29 August

Project starts

12 weeks

Project duration

5million m3

Sediment to be dredged

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