Ground Water Changes Following Quake

There have been marked changes in the groundwater beneath the Canterbury Plains following Saturday's earthquake and the continuing aftershocks, says Environment Canterbury.

New springs have been observed, wells have shown marked increases in water level, spring-fed streams such as the Halswell River have risen markedly and increased turbidity (cloudiness) has been seen in some wells, says Dr Tim Davie, Acting Director Investigations and Monitoring.

"It is well known by scientists that earthquakes can and frequently do induce a response in groundwater that can be observed up to several hundred kilometres from the earthquake epicentre."

The changes are due to several different factors including:
o uplift occurring along one side of a fault line which will raise the water level
o the compression of aquifer material which effectively squeezes water out of the ground
o the generation of a pressure wave through the groundwater that will raise water levels in places
o and the reconfiguration of an aquifer through the shaking of its material.

"Of these, only the last mechanism will produce permanent changes. The first three mechanism produce changes that are likely to last for a matter of days or a few weeks at most," said Dr Davie.
In the past four days scientists from GNS Science and Environment Canterbury have been measuring some of the geological changes and the differences in water levels and streams response. This will continue over the next 7-10 days. In particular a large scale monitoring of groundwater bores will be carried out that will give a better idea of how much of the change is permanent.
“The observed changes do not necessarily give us cause for great alarm at present. We expect the groundwater to settle down over the next week to two weeks and the observations of wells over the next 7-10 days will give us a better idea of any permanent changes,” Dr Davie said.

“We will release the information from these observations as soon as possible to alert water users to potential risks.”
The other factor that may require consideration is damage to well casings and screens. IrrigationNZ have information on how well owners can check for this type of damage. Their website http://irrigationnz.co.nz/

ENDS

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