ORC will be installing groundwater monitoring equipment and extracting geological cores samples to gather new insights into what lies beneath residential South Dunedin and reclaimed coastal parts of the city.

The nine new monitoring bores will bring the total number of bores in ORC’s Dunedin well network to 36 sites, up from four in 2018.

Natural Hazards Analyst Sharon Hornblow said the existing bores had provided useful data on the nature of the ground and water table below Dunedin.

“Our recent investment in groundwater monitoring sites around Dunedin has massively improved how we see the influence of tides and rainfall on shallow groundwater levels across the city.

“This means we have more detail for future groundwater models which look at interaction between deep and shallow groundwater, heavy rainfall and elevated sea level events.”

Senior Scientist – Catchment Modelling Jens Rekker said additional aquifer testing would also take place at the new set of bores.

“For these tests, we’ll actually be pumping groundwater out of one bore and watching the pressure response in nearby bores. This tells us a great deal about how permeable and porous the ground is, and these factors have a large bearing on how the sediments beneath South Dunedin conduct groundwater.

“These tests will help us to understand the connection of different water bodies beneath the surface, which has implications for how we model groundwater level impacts from climate change.”

As well as installing monitoring bores, the drilling at some sites will produce geological core samples. GNS Science will be providing support to analyse the cores as they are extracted, as part of its NZSeaRise Project.

Core samples from deep beneath Dunedin will also aid ongoing research into Dunedin’s geology, for example the reconstruction of past vertical land movements and their implications for future relative sea level change.

Dr Hornblow said the work was part of ORC’s climate change adaptation work programme.

“We need to have a clear understanding of how rising sea levels may affect the bodies of water that lie beneath South Dunedin and reclaimed parts of the city. This will inform future investigations of adaptation options.

“This work also benefits our collaboration with the Dunedin City Council on the South Dunedin Future programme, as it will help inform the city council’s stormwater and other infrastructure planning.”

The drilling work is expected to take about two weeks.