A new cargo wharf and breakwater have recently been completed at Waitangi on the Chatham Islands. Logistics and the severe weather were some of the challenges facing the construction alliance tasked with the project. Richard Silcock reports.
THE CHATHAM ISLANDS lie about 800 kilometres off the south-east coast of the South Island. There are round 600 permanent residents who live on two of the 11 islands which make up the archipelago, with their income derived mainly from fishing, farming and tourism.
The islands are some of New Zealand’s most isolated, with only limited air and shipping services. Local time is 45 minutes ahead of mainland New Zealand.
Due to the poor structural condition of the island’s only cargo wharf facility at Waitangi, the handling of ‘exports’ ($69million) and essential ‘imported’ supplies, such as diesel to fuel electricity generators, aviation fuel for aircraft and food was in extreme jeopardy.
The operator of the wharf was the Chatham Island Enterprise Trust (CIET). In their 2015 Annual Report it is acknowledged the wharf was at the end of its structural life, with degradation of the concrete and corrosion of the steel work and was in dire need of being urgently replaced with a more resilient facility.
Former Internal Affairs Minister, Peter Dunn agreed, saying the wharf had been on the government’s order paper since at least 2011.
“It was a structural risk and needed to be replaced.”
HEB Construction, Downer Construction, Tonkin & Taylor (T&T), Aecom and the NZ Transport Agency (NZTA), all of whom had entered into an alliance back in 2012 for a separate project in Wellington that didn’t proceed, were in a position to proceed without delay to deliver a concept design, secure resource consents and begin planning construction for the facility so were awarded the contract by the client, the NZ Department of Internal Affairs (DIA).*
From the outset it was agreed a breakwater and a larger more weather-resilient wharf and buildings were required with a minimal amount of steel work so as to avoid corrosion.
Detailed design was completed within a tight timeframe by T&T and Aecom and a simulator from the Royal NZ Navy was used to model shipping approach and departure routes for the wharf. The Navy also created a 3D model of Waitangi Bay to see how the wind, waves and tides affected berthing.
“In 13 months we went from having a problem, with an ill-defined scope, to a solution with government funding, design and resource/environmental approvals,” says T&T design manager, Mark Foster.
However, before any physical works could start there was a need for significant logistical planning. The establishment of a quarry on the island was required to provide fill for the reclamation along with a road constructed to reach it.
In addition, accommodation for the 50-plus staff working on the project was needed as there was insufficient on the island to house them apart from a small tourist lodge and a few rental properties.
There was also the logistics of transporting heavy machinery, such as 125-tonne excavators and vehicles to the island from the mainland.
“As with any project of this nature, and especially one on a remote island, it was an exercise in logistics,” says Downer’s project and alliance manager, Hugh Milliken.
“The construction work itself was not particularly difficult,” he says.
“It was the logistics of getting our people and equipment to the island and establishing the necessary supporting infrastructure that created a challenge.
“For example, we had to establish the quarry, which required excavating up to six-metres of over-burden; build a road from the quarry to the port; set up a concrete batching plant and construct a yard to produce three thousand concrete blocks for the breakwater.
“Constructing a large ramp for landing heavy machinery from sea-going barges and setting up transportable accommodation for staff was also required,” says Hugh.
“This took around six months as we had to work in with the shipping schedules and, at times, the extreme weather and sea conditions. We were not able to start construction of the new wharf and port until this was largely in place.”
Construction started in January 2016 with the building of an armour-rock and Xbloc, 180-metre long breakwater, which is positioned 165 metres from the shoreline. Dredging the sand down to bedrock prior to driving nine to 12-metre-long pre-stressed piles to a depth of three metres was also carried out.
The piles, which were cast-in-situ at HEB’s pre-cast plant in Tauranga were barged to the island, while the 6500 square metres of hard-stand land reclamation was achieved using basalt rock from the quarry.
The concrete deck for the wharf was poured to a depth of 300mm over a period of eight months as it could only be done in favourable weather conditions.
“We had to work with the prevailing weather conditions,” says Hugh.
“The often harsh weather precluded working on some days.
“Very little reinforced steel mesh was used in the superstructure and deck. We did not want the new facility to deteriorate like the old one, so the design specification overcame this by utilising a mass pour unreinforced solution where possible.”
A cargo handling building was constructed on the wharf, and a bio-security area and improvements to the livestock race were also made.
“As the port had to remain open to shipping throughout the construction period we had to work around the old wharf which was not demolished until the new wharf was completed and operational,” says Hugh.
“Another interesting aspect of the project was centred around working in a relatively small community and being mindful of the fact our temporary stay on the island affected both the supply and availability of food, diesel and other basic essentials.
“So we took a self-contained approach.
“In addition to providing our own accommodation we also brought in our own food supplies and fuel. Staff were also made aware, for example, that over-patronising the one and only pub on the island could affect their limited supplies so we were very mindful of working in with the local population, building a professional engagement with them and communicating the project’s progress.
“This led to the building of an improved fishing-boat haul-out area and the replenishment of the beach at Waitangi with sand dredged during the piling operation.
“A seabird management plan was also implemented to safe-guard the endangered Chatham Island shag.
“The fact of working on a remote island, getting machinery to it, establishing the support infrastructure, ‘looking after’ the local community and working around the often harsh weather and rough seas were certainly some of the stand-out challenges associated with the complexity of this project.
“Demobilisation and the shipping of equipment and our people back to New Zealand was completed in early May with an all up cost for the project being just under $56 million.”
CIET chief executive, Ian Torrance, says the new wharf will provide a more efficient port operation, encourage future economic growth for the island and help sustain a vital lifeline for the community.
Vanessa Browne, the NZ Transport Agency’s acting general manager for design and delivery agrees and says the result is a credit to the project team.
“The wharf is a cost-effective, purpose-built facility that will help the economic growth of the island and we are proud to have played a part in its delivery.
“We look forward to continuing our involvement by assisting with the maintenance and its operation,” says Vanessa.