The Auckland Council is talking up another one million residents in the city by 2041, but it is taking a prudent line when it comes to providing transport, water and other services.
The council has adopted a Statistics New Zealand's high-growth scenario of a million more residents by 2041, but its water body is using a medium-growth scenario of 700,000 more residents.
The mismatch has raised questions, but council chief planning officer Dr Roger Blakeley says it is prudent to provide for the highest likely population growth and to be cautious to avoid over-investment.
He said the council required council bodies to be cautious about capital spending ahead of time to avoid high borrowing, interest and depreciation costs.
Underspending on infrastructure, he said, could be addressed through regular budget reviews and incremental increases to facilities, such as wastewater treatment plants.
During feedback on the draft Unitary Plan, concerns about a lack of infrastructure planning have been a hot topic at public meetings.
Councillor Cameron Brewer has called for an independent review of the most likely population growth, saying the council's projections are out of kilter with the Government's national infrastructure unit's mid-range projections.
Speaking at a discussion on population growth trends last week, Mayor Len Brown said Auckland's history of exceeding high-growth projection made it prudent to provide for a million more residents.
Auckland's population grew by an average of 2.2 per cent between 1986 and 2011, above Statistic New Zealand's average high-growth rate of 1.8 per cent.
Watercare Services said in forecasting future demand it considered the medium population projection, plus factors such as per capita water use, demand and capacity, which were regularly reviewed.
But in a submission on the council's draft Unitary Plan, the water body expressed concerns about plans for increased intensification of urban areas, particularly the mixed housing zone and the terraced housing and apartment building zones.
"Watercare's network does not have enough capacity to cater for the proposed full development potential of these zones," its submission said.
Auckland Transport, which does use the high-growth projection for its 30-year investment programme, has also filed a submission on the Unitary Plan expressing concerns about the costs of growth.
It said it faced funding issues with a number of existing plan changes relevant to growth in the Unitary Plan and these should not be promoted without identifying new sources of funding. "Otherwise this results in Auckland Transport's $500 million funding envelope coming under increasing pressure to prioritise growth-related projects above others," the submission said.
Auckland Transport also expressed concerns about its ability to service development in the mixed housing zone, which covers 49 per cent of urban Auckland, and a preference for intensification along transport corridors.
A "consensus building group" appointed by Mr Brown believes Aucklanders will by 2015 have to agree on ways to raise an extra $400 million for each of the next 30 years to pay for transport projects needed to keep their city moving under the strain of a million more residents.
1.508m Latest population figure for Auckland
Population by 2041
2.45m approximately an extra 1m - high projection
2.2m approximately an extra 700,000 - medium projection