World's biggest dredge on its way to Lyttelton after Singapore flush out

Wednesday, 27 June 2018

One of the world's biggest dredges, The Fairway, is on its way to Lyttelton Port.

The world's largest trailing dredge will arrive at Lyttelton Port in three weeks to begin a deepening project that has troubled local iwi and surfing groups.

The Fairway has finished its last assignment at Mumbai and biosecurity requirements mean it must go into a dry dock at Singapore to be water blasted for new anti-foul, and the interior spaces cleaned and flushed with fresh water.

Lyttelton Port said it had worked with The Cawthron Institute and ship owner Boskalis to develop the biosecurity plan.

The dredge, Fairway, is being cleaned up at Singapore before coming to New Zealand.

Cawthron biosecurity team leader Oli Floerl said Lyttelton Port had been pro-active in making sure the dredge had minimal biosecurity risk.

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While the Fairway is working, a plume of silt will be visible from the dredge, but Lyttelton Port environmental advisor Jared Pettersson said it would not be bad for the environment.

The environmental effects of the plume were evaluated during the resource consent process and the consenting panel accepted they would be minimal and short-term, he said.

'We have implemented New Zealand's most robust real-time water quality monitoring system,' Pettersson said.

The local effects of dumping the dredged silt prompted environmental and cultural objections during the consenting process from Ngai Tahu about protecting the value of Whakaraupō/Lyttelton and Koukourārata/Port Levy.

As part of the mediated settlement with Ngāi Tahu, the port company will set up a Harbour Watch website providing real-time data.

Lyttelton Port will cease dumping dredge spoil from a previous consent at Awaroa/Godley Head, Livingstone Bay, Breeze Bay and Mechanics Bay which are important breeding grounds for kaimoana or seafood.

The company will also pay Te Rūnanga o Koukourārata and Te Hapū o Ngāti Wheke fisheries enhancement funding of $650,000 over 25 years to benefit mahinga kai or food gathering.

Lyttelton Port will also setup video monitoring of the surf break at Taylors Mistake as a result of mediated settlement with objector, Surfbreak.

The 230 metre-long 30m wide Fairway will widen the navigation channel by 20m and deepen it for vessels with a 13.3m draft. The first stage will lengthen the channel by 2.5 kilometres and will take 11 weeks.

Given its size, the Fairway might have been named after a par-three golf fairway. But 'the fairway', in nautical terms, refers to the deep water channel in a harbour.

Trailing suction hopper dredgers have suction pipes that move over the seabed collecting the sand like a giant vacuum cleaner.

It is pumped into the collection hopper of the vessel and excess water pours out through overflows. The dredge can discharge its load either by spraying it over the front of the bow or dropped out through doors in the bottom of the vessel.

Container vessels currently visiting Lyttelton commonly carry 4500-5000 20-foot equivalent units (TEUs), and that will increase to 5500-6500 TEUs with larger vessels. With further dredging, vessels carrying 8000-9000 TEUs will be able to call at Lyttelton in future.