Fourth bore drilled in South Dunedin

A need to improve the understanding of how sea-level rise may affect South Dunedin has led to another monitoring bore being drilled.

The Otago Regional Council recently installed a fourth bore in South Dunedin, complementing three others drilled in 2009.

The bores, drilled to 6m below sea level, were used to monitor the level of groundwater to see the extent the South Dunedin coastal aquifer was or could be influenced by sea-level rise.

ORC director, engineering, hazards and science, Gavin Palmer said the extra bore at Culling Park supplemented the earlier bores so the council could get a better feel for the distribution of the aquifer throughout the wider South Dunedin area.

''We want to get a better understanding of that.''

The need for a fifth bore was being reassessed to ensure the bores were geographically in the right place.

Unlike other aquifers, South Dunedin's was not used for irrigation so there had been no need to monitor its levels in the past.

The three earlier bores were drilled in a line from Bathgate Park to the corner of Victoria Rd and Kennedy St to determine how far inland the groundwater was influenced by the tides, he said.

A 2012 report on the monitoring results from the 2009 bores showed the water table height in South Dunedin was very close to the surface and that it was under the direct influence of climate and mean sea-level change, plus the drainage provided by the area's stormwater and wastewater drains.

''Groundwater modelling of this effect suggests that even the mildest continuation of the current rise of sea-level rise would create ponding in some parts of the South Dunedin urban area,'' the report said.

It was hoped the additional bores would help to further improve the accuracy of the modelling done for that report.

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