Hinds/Hekeao managed aquifer recharge trial releases first report

The Managed Aquifer Recharge (MAR) pilot project 's first official report has been released and states that groundwater levels around Mid Canterbury have risen and nitrate concentrations have decreased.

What is Managed Aquifer Recharge and how does it work?

Managed Aquifer Recharge (MAR) is not a new concept and has been used extensively overseas.  Infiltration basins, which act like big leaky ponds, are filled with high-quality clean water which seeps down and recharges the groundwater.

Clean alpine water from the Rangitata River is delivered to the MAR site via irrigation races and pipes.  The silts carried by the water settles in the forebay before the water is allowed to flow through to the main infiltration basin (see aerial view below).  From there, the clean water seeps down to recharge the groundwater system. 

The entire surface and groundwater system is carefully monitored for water quality, quantity and ecological health.  Water is not recharged during times of significant rainfall to reduce the risk of lowland flooding.  Likewise, when there is a high demand for water, recharge operations cease.

Where did this idea come from?

The MAR trial has come about as a result of many years of community discussions and recommendations on how to best improve water quality and quantity in the district.  This trial has the support of a diverse group of stakeholders including regional and district councils, Ngāi Tahu, Canterbury District Health Board and Central South Island Fish & Game.  It is managed by the Hinds MAR Pilot Working Group.

Why are we doing this?

While the Ashburton District has some of the most productive farmland in New Zealand, decreasing aquifer levels and increasing nitrate pollution linked to intensive farming have been identified as critical community issues.  This project is just one of a number of on-the-ground actions being taken to improve water quality and quantity in the region.

What the results are telling us

Even within the first six months of the trial a decrease in the concentration of nitrates in groundwater was observed, along with an increase in groundwater levels.

Since then, the trial’s first official report has been completed and presented to the Ashburton Zone Committee in late August 2017.

The results show groundwater levels around recharge site have risen around five metres and nitrate concentrations have decreased.

Chairman of the managed aquifer recharge (MAR) group Peter Lowe told the Ashburton Guardian the trial had achieved two of its three goals, and was close to realising the third.

“We reduced nitrates in the command area significantly, we raised groundwater levels significantly and we are not far off getting the water into the headwaters of the coastal drains.”

For the full story see: www.guardianonline.co.nz

Key report findings

  • Total recharged water during the first year was 2.4 million cubic metres
  • Increased groundwater levels have reached about 7km downstream from the pilot site
  • Nitrate levels in the groundwater decreased from 4g/m3 to less than 1
  • Nitrate levels down gradient influenced by the pilot reduced from 14 to 4.

You can read the full report and summary below.