Climate change News

Long-term threat to South Dunedin has not gone away

Green Party candidate for the new Taieri electorate Scott Willis is warning that a new report on surface flooding in South Dunedin should not lull the community and officials into a false sense of security.

With water all around, we need to understand the options we have, and prepare

– Scott Willis

“The threat hasn’t gone away, but our understanding of it has improved, thanks to great work by the GNS team” he said. As the report states, “Problems of surface flooding and groundwater inundation in low-lying parts of Dunedin are expected to increase with climate change.”

Flooding in South Dunedin
Flooding in South Dunedin during 2015

A new study

The new study from GNS Science has found that conditions that lead to surface flooding in South Dunedin are not as straightforward as previously thought. After a year of data collection from 23 boreholes, GNS has found that the soil beneath South Dunedin is not as permeable to rising tides as people had believed. This is useful to know because a 2015 report from the Parliamentary Commissioner for the Environment found that 2683 houses in Dunedin were less than half a metre above high tide – more than twice the number in Auckland, Wellington and Christchurch combined.

“South Dunedin is built on what was once tidal wetlands and now supports a diverse community with a strong sense of pride and deep concern about the future. This isn’t surprising with threats directed at South Dunedin from the harbour, sea and hills, all at once. With water all around, we need to understand the options we have, and prepare” says Scott. Indeed, as the report states, South Dunedin is the New Zealand urban area at most extreme risk, because “groundwater beneath South Dunedin and Harbourside’s narrow coastal strip is faced with encroachment from all directions: the harbour in the east, the ocean in the south and changing runoff- and recharge- related flows from hill catchments in the north and west”.

South Dunedin flooding during 2015
South Dunedin flooding during 2015

The GNS study tells us that we have a bit more time to adapt to the rise in sea levels. The report’s main author Simon Cox reported on Radio NZ that “over the short to medium term, having less permeable ground and less water flowing through there, means that there will be a wider range of options that they can use for engineering to keep things going maybe over two to four decades.” But the water table under South Dunedin will continue to rise and the capacity of the soil above it to absorb extreme stormwater will therefore continue to reduce.

Scott is urging immediate and widespread action and support for community-led development of the low-lying areas so that the community can actively participate in and shape adaptation solutions. “Climate justice means ensuring our community has the power to participate in solutions rather than having decisions imposed. We need to be thinking ahead” he says, “The creativity and power of our community is something we can harness for good.” In the long run the best hope for South Dunedin is that New Zealand can show the world the same leadership on climate instability that it has in managing the Covid-19 pandemic. South Dunedin needs to be the first to show the way.

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