Ports of Auckland could be moved to a new "super port" in the Manukau Harbour or the Firth of Thames at a cost of $4 billion to $5.5 billion.
That is one of the main findings of a Port Future Study report due to be released tomorrow and obtained by the Herald.
The report is not confident that Ports of Auckland can continue operating at its current downtown location and says a new site needs to be found.
What's more, Tauranga and Northport ports will be unable to cope with the growth in Auckland freight together with their own demands.
The Port Future Study - made up of representatives from business, Ports of Auckland, community groups and iwi - has narrowed down the possible new port locations to Manukau Harbour and the Firth of Thames, subject to more detailed investigation.
In the short to medium term - between now and 2065 - the report recommends no further reclamation at the Fergusson container terminal but a need for extra berth length at Bledisloe Wharf for vehicle imports and other bulk cargo.
The report does not make any specific recommendations, but discussions have taken place among the port study's consensus working group and wider reference group for an extension of about 25m between two concrete piers at the end of Bledisloe Wharf to create a new east-west berthage space. Ports of Auckland are understood to be seeking a 65m extension.
In recent years the port company had pushed for extensions to Bledisloe Wharf of up to 179m.
The report found that retaining the bulk of port functions is better than shedding cargo elsewhere or downsizing in the short to medium term. Shedding or downsizing freight operations may weaken the case for moving the port, it said.
Cruise ship facilities should be kept and improved in central Auckland and a carparking building is one option to moving the importation of cars to Northport or Tauranga.
The report, commissioned by Auckland Council following last year's battle over wharf extensions of about 96m into the Waitemata Harbour, has made a number of recommendations that will be considered by the council's Auckland development committee next week.
Port opponents won a historic victory after the High Court at Auckland ruled consents for the project were invalid. The Herald has campaigned against further reclamation of the harbour for port use.
The report's recommendations include establishing a port relocation site, further investigations into the preferred Manukau and Firth of Thames sites and regular monitoring of trigger points to find the best time to move the port.
Auckland must decide soon how to provide for the future growth of port capacity
"Auckland must decide soon how to provide for the future growth of port capacity and about the implications of that long-term strategy for short term port development plans," the report said.
The report said the port should move when the social, environmental, cultural, economic, urban development and other conditions are right for the city centre or Auckland or New Zealand.
It was also possible that Auckland's future unfolds in a way that does not trigger the need to move and it can accommodate the long-term demand at the current site.
In the 2014-2105 year, Ports of Auckland handled 970,000 containers, three million tonnes of freight and 250,000 cars.
The number of containers is expected to grow to three million over 50 years and "considerably beyond three million" over a much longer time period, the report said.
The report found three constraints to the port's volume growth - the footprint required to operate the port, berth lengths to accommodate more visits by larger cruise and cargo ships, and transport connections.
Growth of two to three times current volumes might require the need for large investments in fly-overs or trenching because of space constraints, and to limit adverse effects for local communities and landowners.
"The potential for trade growth, uncertain productivity improvement potential and limits to expansion mean that the CWG (consensus working group) cannot be confident that the port will be able to accommodate long term demand growth on its current footprint," the report said.
A new port in the Manukau Harbour or the Firth of Thames could handle 10 million containers.
The report said the port might be able to relocate during the 2030s , at a "sweet spot" during the 2040s or later in 2055.
What the report says about the two new locations
• Highest ranked option in a consultant's report.
• Of three sites - an island port in the upper harbour, central harbour and Puhinui - Puhinui is the highest ranked.
• Manukau is the closest location for freight movements providing lower freight costs for consumers and industry and increased competitiveness of exports.
• Will trigger concerns about the Manukau bar and channel which will require dredging and ongoing maintenance costs.
• One assessment found a port would be feasible and safe, but more detailed engineering work was needed.
• A safer and more reliable channel would potentially increase use by recreational, tourism and fishing boats.
• Manukau would involve a major shift of shipping patterns and extra shipping costs.
Communities and mana whenua are unlikely to welcome a new port in the Manukau with a contentious history of environmental care and remediation.
Firth of Thames
• Kawakawa Bay was preferred to a location near Waimango Point.
• Higher transport and freight costs.
• Location would raise important cultural, social and environmental issues.
• A transport route to the coast passes through a rural environment that would be substantially altered by large scale roads and rail links.
• Could open up land relatively close to Auckland for development.
• Could become a "super port" serving the upper North Island, including Tauranga.
Impacts for both locations
• Important challenges and high costs need to be considered to provide cost-effective facilities and freight services for New Zealand's trade and economic well-being.
• Gaining support from mana whenua and others present a significant challenge.
• High costs to move the port and constrained funding, although some costs could be offset by sale of current port land.
• Consideration could be given to funding the land component separate from the operating company, which may allow equity participation by council and iwi.