Water in Marlborough aquifers rises after 7.8-magnitude earthquake

Marlborough aquifers

Marlborough aquifers

Water levels Marlborough's aquifers and wells have leapt up since the November earthquake - causing equipment to break and some wells to overflow. 

Wells and aquifers in the region's southern valleys have been reading water levels off the charts, with some monitors broken. 

A council scientist said the gaps between the gravel that formed the aquifers had shrunk, causing wells to spill over. 

For the first time ever, water began to flow out of a deep layer well connected to the Brancott Aquifer.

For the first time ever, water began to flow out of a deep layer well connected to the Brancott Aquifer.

It was too early to say whether the 7.8-magnitude quake had caused any permanent damage to the underground water network.  

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Marlborough District Council scientist Peter Davidson said at this stage it did not appear any of the aquifers or wells were damaged, apart from a well at Needles Creek, in Ward, which was completely destroyed. 

The well has since been fixed.

The well has since been fixed.

It was a "passive monitoring well" and was not a source of drinking water.

"The reason for establishing the well was to get a baseline indication of groundwater conditions," Davidson said. 

Davidson said an aquifer based in Ben Morven had risen by 4 metres, while water in another aquifer had risen by 5.5 metres. 

"It destroyed our monitor," Davidson said.

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The council had been able to take spot readings of the site to monitor the amount of water in the wells, he said. 

Water had come "rushing up" wells, causing the water in some of them to rise by 4 or 5 metres, and seep onto the ground. 

Even without the earthquake the level in Marlborough's southern aquifers had been rising, thanks to the Southern Valleys Irrigation Scheme, which sourced water from the Waihopai and Wairau Rivers rather than the aquifers, Davidson said. 

The scheme was constructed to provide irrigation water to horticultural and farming operations over an area of approximately 4500 hectares to the south of Renwick.

"We have had a reasonably good winter and spring in terms of recharge," Davidson said. 

"We are still learning from the Christchurch quakes what effects they have, so it's early days." 

Straight after the earthquake turbidity had been a problem in Marlborough aquifers, in both coastal and inland areas of the Wairau Plain.  

However that had calmed down now. 

The readings from the aquifers in southern Marlborough showed one of the benefits of the irrigation scheme had been that it allowed the aquifers to replenish. 

There was water "in the bank" if farmers ever had to draw on it again, he said. 

Most of the aquifers in the Marlborough area were in southern Marlborough, with the largest being the Wairau Aquifer which supplied both Blenheim and Renwick.

There was a smaller aquifer in Havelock. 

He believed it was "close to capacity", but was not formally monitored as other aquifers were, Davidson said. 

In northern Marlborough the council looked at river flow, rather than storage, he said. 

Apart from the township of Renwick, which was experiencing falling water supply in its wells and rising consumption, Marlborough looked to be in a good position for the summer.

"The take home message is that water levels for that [Renwick] aquifer are higher than they were a year ago," he said. 

 - The Marlborough Express


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