Well supplies data but no water

Press, 31 August 1989, Page 7

Well supplies data but no water

By

JANE DUNBAR

Two million years ago sea levels in the Christchurch area were higher than today, according to information gathered from a well being sunk to new depths below the city. The well, at Bexley, is down to a depth of 300 m and the contractor is expected to have drilled down to the planned 400 m by October. It is being sunk in a search for more water for Christchurch. The city’s water supply is drawn from four aquifers down to 150 m deep. It is hoped there will be up to another four aquifers between 150 m and 400 m. The results of the search for water had been disappointing, said the North Canterbury Catchment Board’s acting resources’ manager, Mr John Talbot. But interesting information had been gathered about the past climate of the Christchurch area. Good examples of cockle and mussel shells had been found at a depth of 250 m to 300 m. They were two million years old and looked the same as shells did today, said Mr Talbot. Pollen samples taken also showed the climate was similar to today, but a bit warmer with sea levels higher and the sea further inland. Mr Talbot said a layer of water had

been found about 230 m, but it was “very, very old” water and probably not usable. There was better news at 292 m where another layer, similar to the water being used from higher aquifers, was discovered. “It is very surprising we haven’t found the regular layers of water like there are down to 150 m,” said Mr Talbot.

“We have consistent layers of clays, gravels, clays, gravels down to 150 m. But from 200 m to 300 m there are only very thin layers of gravels at 230 m and 290 m and the rest is a vast thickness of clay.

“There doesn’t seem to be the groundwater we were expecting. But of course there is always the possibility there is more further down.” A Reader in Geology at the University of Canterbury, Dr John Bradshaw, said that the Bexley well was of scientific interest, but the information gathered was not surprising. Climate fluctuated continually, and there had been both warmer and colder periods in the past. About 6000 years ago the shoreline had been as far in as the University of Canterbury, and 1200 years ago it had been way out beyond New Brighton, he said.