But a recent report for the Otago Regional Council notes that this alone does not mean there is good ground in Dunedin’s lowest-lying suburb either.
Analysis of data from 22 bore sites around South Dunedin showed soil across the area was likely too plastic to liquefy, but the geotechnical engineering report noted significant areas in South Dunedin were not "good ground".
Otago Regional Council natural hazards analyst Sharon Hornblow said the council now understood a lot more about the variability of ground conditions in South Dunedin, which suggested detailed mapping of the area was the wrong approach.
Even though overall widespread liquefaction was unlikely, there were likely pockets of ground in the suburb where liquefaction and settlement would occur.
"We can also see that there is not a distinct pattern of high and low risk of liquefaction and settlement," Dr Hornblow said.
"This high variability - and the formation of the area over time with small interspersed streams, sand dunes and terraces, wetlands that have been filled in, and so on - makes mapping in detail less useful than site-specific investigation of individual properties."
Council natural hazards manager Jean-Luc Payan earlier this month said the regional council remained in discussions with the Dunedin City Council about the best way to use the analysis for planning.
But the report the regional council commissioned, and the council’s broader work into the varied risks in South Dunedin and the harbourside area, could help guide decisions about the future of the area.
While seismic risk was not as extensive as some feared in South Dunedin, there were issues that would be problematic for individuals and property and a multi-hazard approach was required, Dr Payan said when he presented the report to regional councillors last year.
"It’s true it’s better than what we previously thought, but there are still issues," he said.
"They are manageable issues, but there are still issues that need to be carefully managed."
In 2004, the regional council began sea-level monitoring at Green Island.
In a related programme, in 2009, groundwater and geology in South Dunedin began to be monitored as four bores were drilled in the area.
But in 2018 and 2019 monitoring increased significantly; there were now 22 bores in the area.
The council needed a better understanding of the underlying conditions in South Dunedin, he said.
More work was also needed in the reclaimed harbourside area, a critical area for the city that might face the same issues as South Dunedin, he said.
Related Stories
Comments
Yes in Dunedin urban the lowest but to the north in Waikouaiti a proposed development of a former horse training property with a flood-prone water table lurking just below the surface, has made the first step towards a 50 house development.
This area is just behind the sand dunes & is closer to the sea than South Dunedin, the distance is less than 250 metres from high tide.
From all the information available this defies all logic & local people's memories of flooding, this year has seen lower rainfalls but what of the near future?
The traffic has increased over the years with no roading improvements in Beach St. So along with increased water usage, sewage, directed storm water, power requirements & traffic flows you can see why there's a degree of angst amongst residents.
Liquefaction settlement, raising sea water levels, a catchment stream that when flooding spills out into surrounding homes passes through the proposed housing blocks, this non notified development is going to be interesting in the years ahead.
Yes South Dunedin as we know it was formed in the past, the DCC now has future same situation about start again.