February earthquake has greater impact on groundwater levels in Eastern suburbs

Environment Canterbury’s groundwater monitoring team has been examining groundwater levels monitored around Christchurch following the earthquake of 22 February.

An initial analysis of the data shows there were significant changes in groundwater levels in eastern Christchurch, but that groundwater has returned almost to normal in most cases.

Ken Taylor, Director of Investigations and Monitoring at Environment Canterbury said the records have revealed sharp contrasts between the September and February earthquakes.

“We have recorded quite noticeable but relatively short-term spikes in groundwater levels in the eastern suburbs – increases of around four metres in some places. This is not particularly surprising considering the proximity of the earthquake and the exceptional ground accelerations.

“This result is different to what we noticed following September’s earthquake. The effects of the February earthquake were more localised to the east, while the September earthquake had a greater impact in the west of Christchurch,” he said.

Nonetheless, initial results suggest there has been little long-term impact on groundwater levels in the Christchurch area from either earthquake.

“From the September earthquake we have found there is little evidence so far of any long-term effect on groundwater levels and we believe this is the same with February’s,” said Ken Taylor.

Recordings taken at Ensors Road and Dyers Road sites in February saw significant changes (rises of up to four metres) in groundwater level. These wells also took much longer to return to a typical depth than others.

Ken Taylor said an inspection of the damage to the city’s wells needs to be carried out to provide a more definitive representation of the effects of February’s earthquake.

“A few wells have taken longer to return to normal after February’s quake, and this may be a result of the well having been blocked by silt or other debris,” said Ken Taylor.

Environment Canterbury’s groundwater monitoring team is planning to visit sites to check for blockages and damage to monitoring equipment in the coming weeks while still attending to monitoring the rest of the region.

For a copy of the report visit:
http://ecan.govt.nz/publications/General/earthquake-impacts-groundwater-update-1-130411.pdf