Residents can also expect disruption and change, as the low-lying area adapts to climate-related hazards, such as rising groundwater and more-intense rainfall.
Seven adaptation options have been narrowed and adjusted to a shortlist of three, which have price tags ranging from $1.63 billion to $2.45b over 100 years, it has been estimated.
In each case, costs would be front-loaded in the first 25 years and benefits would build in later years.
Pressing on with a status-quo approach instead would be worse value for money, as bills from storm damage would mount, media were told at a briefing before the release of several reports this morning.
The briefing came from the South Dunedin Future programme, which is run jointly by the Dunedin City Council and Otago Regional Council.
Councillors from each council are due to discuss the material next week and it is expected there will be public engagement about the proposed options from July 1 until August 9.
A resulting climate adaptation master plan is expected to be presented to the councils for approval in mid-2027.
South Dunedin Future programme manager Jonathan Rowe said analysis had generated a more comprehensive picture of what it would take to manage flooding in one of Dunedin’s most complex and exposed urban environments.
‘‘The encouraging finding is that, even as flood hazards increase, it is feasible to significantly reduce risk — potentially to levels comparable to, or lower than, today,’’ Mr Rowe said.
‘‘However, achieving that outcome would require sustained effort over many decades, including major investment, disruption and change.’’
Sticking with the status quo could lead to the average annual cost of damage swelling from about $11 million to as much as $212m long term, the programme’s presentation said.
The three proposed options for change were given one-word titles — protect, restore and reshape.
There are common elements across the options, such as at least 14ha for water storage and wetlands, and more than 1000 buildings needing to be demolished.
Land would have to be acquired for public works.
Differences include the extent of land that would need to be repurposed, whether some land should be elevated and whether there should be 3.5km of open water channels introduced.
The ‘‘protect’’ option would focus on engineered systems, while ‘‘restore’’ would seek to make space for water.
‘‘Reshape’’ was considered the most transformative option, involving raising land and creating green spaces and waterways.
In a joint press release, the councils acknowledged community frustration regarding perceived lack of action about flooding since 2015.
It had taken time to build a comprehensive understanding of underlying problems and to identify workable long-term solutions, the councils said.
‘‘Restore’’ had the cheapest estimated cost over 100 years, at more than $1.6b.
The estimated cost for ‘‘protect’’ was above $2b and more than $2.4b for ‘‘reshape’’.
South Dunedin Community Network chairman Mike Hammond said though it was early days, general community feedback was largely supportive of green spaces and water retention in the three options.
Before a final decision, councillors should consider the importance of community health and mental wellbeing, ‘‘as well as fiscal restraint’’, he said.
Insurance Council of New Zealand resilience leader James Baigent said the insurance sector backed the city and regional councils’ proactive, evidence-based approach.
Collaboration would be crucial, he said.
‘‘From an insurance perspective, the key difference compared with the status quo is that all three options involve taking action to reduce underlying risk,’’ Mr Baigent said.
‘‘By acting early, the councils’ reports show upfront investment in risk reduction can avoid significantly higher future costs and disruption.’’
