What lies below? Drilling to begin in South Dunedin

Gavin Palmer
Gavin Palmer
Twenty 15m-deep holes will be drilled across South Dunedin from next week as a group of organisations joins forces to discover conditions beneath the surface.

The work is part of initiatives to prepare for storms, earthquakes and sea level rise as the city prepares to mitigate and adapt to those issues.

Residents will see ''core penetration testing'' rigs transported by truck to the suburb as drilling takes place.

The work will mostly take place on road berms.

Once in place, piezometers - pressure-sensitive tubular instruments that record the subsurface groundwater pressure - will record the water level every 10 minutes to allow precise tracking of water movement.

That can then be matched more accurately against rainfall and tide timings.

The work is being undertaken by EQC, GNS Science, QuakeCORE, the Dunedin City Council, the University of Otago and the Otago Regional Council.

EQC senior adviser John Scott said the results of the study would help the understanding of the effects of rainfall and tidal movement on the water level under the ground, and how the soil might behave in an earthquake.

''With solid scientific data from this project, the community can make better decisions on how to reduce risk,'' he said.

''For example, we will have a much better idea of how wide and deep building foundations should be to handle conditions in an earthquake.''

Otago Regional Council engineering, hazards and science director Gavin Palmer said some data, like geotechnical information, would be available immediately as work began.

Hydraulic data would be gathered over time.

''As well as giving us a better understanding of what's going on now, the testing will help develop better computer models of the impacts of future storms and sea level rise,'' Dr Palmer said.

''This in turn lets us better understand options to mitigate against and adapt to these effects in future.''

A city council spokesman said the cost of the work was $54,000, and EQC was the primary funder.

In terms of what people would see, the cone penetration testing rig would be transported by truck, then moved around so that drilling could take place.

The installation of each piezometer would take several hours, but would not involve major disruption.

The piezometers were about 50mm in diameter, and once they had been set into the ground, they would be sealed with a lockable cap, similar in appearance to a water toby cap.

City council 3 waters group manager Tom Dyer said the DCC had budgeted $35million for flood alleviation in South Dunedin over the next 10 years.

''The piezometer data will help inform options for exactly what that money should be spent on.

''The information will also be useful in preparing for an imminent flood, as response agencies will have a better idea of how much capacity the ground has to hold rainwater at any given time,'' Mr Dyer said.




Drill holes do what you like/ the areas sinking ///// that wont be fixed/

South Dunedin is not sinking, philip beckgreymouth. It is a fake story from the scaremongers at the DCC, ORC and GNS. South Dunedin has no high quality GPS survey points, so there is no evidence for this claim. Also, the ORC has found no evidence that the South Dunedin ground-water level is increasing - there has been no change over the several years of monitoring. The problem with flooding will be completely fixed when the DCC upgrades the ancient and failing stormwater system - nothing else needs to be done.

I don't think so///////////