The Dunedin City Council is planning for a challenging future in South Dunedin.
A council-commissioned report by Beca, made public last year, had already spelled out the need for a $75 million network of pumps and wells to protect against rising seas and groundwater over the coming decades.
Council services and development general manager Simon Pickford said attention was now turning to ''what non-protection options might look like'', he said.
That would be followed by a cost-benefit analysis of the various options, which would be presented publicly for community discussion, he said.
''Adapting to the effects of climate change will be a long and iterative process and while no significant decisions are expected to be needed in the short term, it is prudent for the council and community to start thinking about and planning for the longer-term effects now,'' he said.
That process would also be informed by the Otago Regional Council, which has in recent years drilled four bore holes in South Dunedin to study the area's water table.
Dr Gavin Palmer, the ORC's director of engineering, hazards and science, told the ODT the bores had confirmed a relationship between the level of the sea, and the level of groundwater in South Dunedin.
In layman's terms, when the tide came in, the groundwater level rose, and that trend was expected to be exacerbated by climate change and sea level-rise over time, he said.
''As the sea level rises, we would expect groundwater levels in some parts will also rise to a new normal level.''
The bores showed the groundwater was 93% seawater closer to the coast, but much closer to freshwater further inland.
Additional work was needed to understand in more detail what was happening underground, but the work would inform future decisions ''about how to occupy South Dunedin'', he said.
''What comes out of that remains to be seen, in terms of who would do what.''
DCC city development manager Dr Anna Johnson said the council's second generation district plan also sought to place limits on development in coastal communities under threat, including South Dunedin.
That included ''questioning ... whether long-term we want a lot more people living there''.
Changes to floor levels, and the requirement for relocatable homes, in South Dunedin were designed to ensure residents were ''safe in the meantime, and [able] to leave eventually if they need to'', she said.
Those initiatives were not limited to South Dunedin, but the suburb was a special case.
''The compounding factor with South Dunedin is it's in a basin. Not only does it have a high water table ... it also has a big catchment of water feeding into it, so it's probably even more vulnerable than some of the other areas,'' she said.
The council needed to find the balance between maintaining infrastructure in South Dunedin and considering longer-term options.
While that did not yet include planning for managed retreat, it was possible it could happen organically as conditions changed and market forces, and insurers, reacted, she said.
Christchurch's Red Zone approach was unusual, and the more common approach - as found in storm-threatened coastal communities in the United States - was a gradual shift, she said.
Authorities there had protected existing-use rights, but prohibited the rebuilding of storm-damaged homes, to encourage a gradual transition, she said.
''Slowly, over time, there's fewer and fewer houses as more and more of them get damaged and can't be rebuilt.
''I don't know if that's how it would go in South Dunedin ... but generally it's something that evolves, rather than one day everyone packs up and leaves.''
Council water and waste group manager Laura McElhone said a rising sea level, bringing with it a corresponding rising water table, would only exacerbate problems in South Dunedin.
More heavy rainfall, with less dry ground for it to soak into, would mean the area's pipes were overloaded more often and to a greater extent.
''It certainly creates a whole heap of extra challenges. It does increase the risk of certain areas flooding ... it's just got nowhere to go,'' she said.
In the meantime, council water staff would continue to invest in the renewal and upgrade of infrastructure in South Dunedin, she said.
Managed retreat was ''most certainly a political call'', and staff were focused on ensuring the network performed as well as it could.
''Questions about whether or not certain areas will still be there have not made any difference to that planning.
''That's something for the politicians to debate and decide.''
