- Published: Tuesday, 20 April 2021 15:23
CentrePort is undertaking work to remove a build-up of sand in Wellington Harbour to ensure shipping has sufficient depth to operate, improving safety and efficiency.
CentrePort General Manager Logistics Mark Thompson says ridges of sand have built up over several years in two areas of the shipping channels in the entrance to the harbour and need to be removed to improve the safe and efficient movement of vessels.
“The build-up has been caused by propeller wash in two areas located in stretch of water between Pencarrow Head and Seatoun which means deep draft ships are having to deviate from the usual entry and exit routes.
“Removing the sand will return the harbour to its original depth in those two areas allowing ships to use the established entry and exit shipping lanes,” Thompson said.
The Dutch Dredging company vessel Albatros will do the work which is scheduled to begin Thursday 22 April and take three-to-six days to complete.
“Wellington is the busiest shipping harbour in New Zealand with more than 7000 commercial vessel movements (inter-island ferries, container vessels, fuel tankers, bulk cargo vessels) every year,” said Thompson.
Approximately 22,000 cubic metres of sand will be removed to return the channels to their previous depth. The sand will be deposited at a site near CentrePort’s Thorndon Container Wharf – previously used for depositing dredged material from the berths at Aotea Quay following the 2016 Kaikoura earthquake.
Greater Wellington Regional Council has granted resource consent for the project covering areas such as care for the environment, maintenance of health and safety, and engagement with Te Whanganui a Tara iwi.
This is the first shipping channel maintenance required in Wellington Harbour since 1968 when 264,000 cubic metres was removed. Most New Zealand commercial ports require the regular removal of built-up material annually.
Why is the channel maintenance necessary?
Sand caused by propeller wash has built up in two areas of Wellington Harbour in shipping lanes used by vessels to enter and depart Wellington Harbour.
This has reduced the depth of the Harbour in these relatively small areas (1045m x 85m wide, and 500m x80m) to less than the required minimum for safe clearance for deep draft vessels. These vessels are currently having to navigate around the shallow areas which is inefficient and reduces options in case other shipping needs to change course.
The work will return the shipping channels to their previous depth.
How will the material be removed and where will it go?
The vessel Albatros operated by the company Dutch Dredging will do the work. A pipe is lowered to the targeted areas and the sand is sucked up onto the vessel. The vessel will make a series of trips to an area off Thorndon Container Wharf to deposit the material. This area was used for depositing sand following the 2016 Kaikoura earthquake.
Why has the deposit site off Thorndon Container Wharf been chosen?
The site was previously consented in 2017 for depositing material removed from the berth pocket at Aotea Quay following the 2016 Kaikoura earthquake. The site was chosen because of its depth and stability. The site is not impacted by currents and ship movements which means the material does not drift to other parts of the harbour.
How long will it take?
The work is scheduled to take three-to-six days depending on weather and sea conditions. The Albatros hours of operation will be between 6am and 6pm.
Will it cause any disruption to commercial shipping/recreational use of the harbour?
There will be no disruption. CentrePort and the Harbour Master will keep harbour users informed of the work. The sound levels will be no greater than usual commercial shipping activity.
What about the environment?
The project has been granted resource consent by the Greater Wellington Regional Council. This includes managing operations to protect the marine environment.
Environmental scientists and the Department of Conservation were part of the review of aquatic ecology impacts to ensure preservation of marine flaura and fauna.
Wellington Water was involved in the consenting process to ensure there is no risk to mapped aquaifiers / springs.
How does this work compare to previous Wellington Harbour maintenance?
This is a small project in comparison to previous removal of material in shipping channels in Wellington Habour. The previous maintenance was in 1968 when 264,000 cubic metres of material was removed – 13 times the amount of material that may be removed in this work. The original dredging of the harbour took seven years (1904-1911) when 7.8 million cubic metres of material was removed.
Why is the maintenance of the shipping channels in an out of Wellington Harbour important?
The movement of maritime traffic is critical to our economy and the movement of people between the North and South Islands. Ensuring the channels are maintained at the appropriate depth ensures the safe and efficient movement of shipping.
Wellington is the busiest commercial shipping harbour in New Zealand. Between ferries taking people and cargo between the North and South Islands, container ships carrying imports and exports, and fuel tankers and bulk cargo vessels delivering vital cargoes, there are more than 7,000 ship movements per annum in Wellington Harbour.
That activity is critical to the prosperity of not just Wellington, but the New Zealand economy. Over a million people travel by ferry between the Islands each year, and cargo valued at $20bn is transported per annum.