Water secured for aquifer recharge

Water flows into the first of two ponds at the managed aquifer recharge (MAR) site near Tinwald. Photo: John Keast
Water flows into the first of two ponds at the managed aquifer recharge (MAR) site near Tinwald. Photo: John Keast
Ashburton's managed aquifer recharge (MAR) trial - the first in New Zealand, and one which may put water back into the Hinds River and boost rural supplies - has a secure source of consented water until 2021.

Ashburton District Council, without dissent, granted the Hinds MAR governance group use of up to 500 litres a second of consented but unused stockwater from the Rangitata.

Approval ceases on February 25, or earlier, if sites transfer to a commercial entity.

The water can only be used for aquifer recharge or other related initiatives.

A year ago, when the governance group sought a four-year extension to the water, it was kept by the council to a year and asked to come back.

There was also an attempt, then, to limit its supply to 125 litres a second.

There was no such bid this time.

Councillors were addressed by governance group leader Peter Lowe, scientists Bob Bower and Dr Brett Painter, and ECan member David Caygill.

Mr Lowe said MAR was a quiet achiever, gaining results that were largely unseen.

It began with a council-owned infiltration site near Tinwald, where water percolates into the ground to boost aquifers and cut nitrate rates, and has spread to 16 new test sites, with water from the Rangitata diversion race, Barrhill Chertsey Irrigation or MHV Water.

The trial has been successful.

Over two years, a total of 4296 cubic metres of water has been recharged - 1700 Olympic-sized swimming pools.

Preliminary groundwater quality results show an ''expanding plume'' of clean water and nitrate-nitrogen levels have dropped from an average of 14g/cu m to 4g/cu m.

E. coli has not been detected in the clean-water plume.

The group said the trial was significant in that it was running in dry and wet periods.

The group has now installed and is testing 16 new sites to determine the recharge potential across the Hinds Plain.

Each site is consented to recharge up to 50 litres a second, and a new recharge project next to the south bank of the Hinds River has been designed with Te Runanga o Arowhenua.

That project will recharge up to 200 litres a second with water from the Rangitata and it is hoped it will increase flows in the river and associated springs.

The project will also re-establish native vegetation on the floodplain, improve water quality and recharge clean water into a groundwater system associated with drinking water supplies - Mayfield.

The Hinds recharge area is below a siphon downstream of the RDR and near the Hinds, near Mayfield.

Mr Lowe said the results of the trial were outstanding, and compounding.

He said the trial was a logical, efficient use of water to achieve environmental standards.

The trials are supported by the Ashburton council, ECan, Ministry for Primary Industries, Lincoln Agritech, the Canterbury District Health Board, contractors and irrigators.

-By John Keast

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