New Zealand’s largest managed groundwater rehabilitation project is getting bigger.

The Hekeao/Hinds Water Enhancement Trust (HHWET) has been granted leases for two new sites, and renewed the use of a third, to continue its work on improving groundwater and river quality in the area.

HHWET chairperson Peter Lowe said gaining the leases is a step towards expansion plans and continuing to have a positive impact on the ecosystem's health.

“Our year six annual report clearly shows that the projects undertaken by HHWET in line with its goals, can and do make a positive difference to the Hekeao Hinds Catchment."

HHWET is a community group set up to manage large scale groundwater rehabilitation projects across the Hekeao/Hinds Plains.

These projects include managed aquifer recharge (MAR), near river recharge (NRR), and targeted stream augmentation, with a goal of enhancing groundwater quality, improving baseflows to spring-fed streams and rivers to improve ecological, cultural, and social values, and to improve and sustainably manage groundwater storage levels.

HHWET executive director Brett Painter said while water quality gets a lot of focus, HHWET is aiming to improve “the quality and the quantity, the critters in there, the whole picture – the whole ecosystem”.

A key indicator of the project success is the Hinds River.

“Where we have made the most measurable difference is in the Hinds River because that system moves quickly while groundwater systems move incredibly slowly and are vast,” Painter said.

Analysis of annual average flows at a site before and after MAR/NRR produced a 112% increase in average flow for the 2020/21 versus 2015/16 ‘dry’ year comparison, he said.

“We more than doubled the flow and that will have had a significant impact.”

HHWET started with just one MAR pond in 2016 and has expanded its site numbers to 15.

They have applied to Environment Canterbury for resource consent to operate MAR sites at 34 locations, 14 existing and 20 new sites.

“We will stage the next phase once consents are confirmed,” Painter said.

Once the resource consents are obtained, HHWET intend to construct soakage pits on each site for managed aquifer recharge (MAR).

MAR sites are infiltration basins, which act like big leaky ponds, which are filled with high-quality water that seeps down and recharges the groundwater, and in turn enhances quality and replenishes aquifers.

At the pilot site the groundwater nitrate levels were between 6 and 7mg/l before in the area before the project started and they are now 1.2-2.2mg/l when the site is operational.

“We can expect similar concentrations immediately down-gradient from other MAR sites,” Painter said.

Granting the three leases are the council’s latest contribution to HHWET’s efforts, having previously provided the use of council consented but unused stockwater, funding, and use of council land for projects.

Residents in the area contribute to the project through Environment Canterbury’s (ECan) targeted rate, currently its only source of funding after its Provincial Growth Fund money ended last year.

By Jonathan Leask