Gisborne District Council's Makauri aquifer Managed Aquifer Recharge (MAR) trial aims to inject water from the Waipaoa River into the Makarui aquifer to ensure its ongoing use for irrigation of 3000 hectares of horticultural farmland.
Funding and resource consent has been approved for Council to proceed with stage 2 of the MAR trial.
Stage 2 will fully investigate potential risks and inject up to 360,000m3 from the Waipaoa River into the aquifer.
As part of the resource consent and ECT funding conditions, Council is engaging with Rongowhakaata Iwi Trust around the development of a cultural impact assessment.
A Mauri Compass assessment of the trial will be undertaken as part of the cultural framework agreed with Te Aitanga a Mahaki.
A successful pilot trial has proven the feasibility of MAR in the Makauri aquifer. Work is now underway to proceed with stage 2, which will fully investigate all potential risks.
It proposes to run over 2 and a half years and inject up to 360,000m3 per year, depending on river flows.
The trial will generate hydrological data needed to determine the number and location of injection bores in a wider MAR scheme.
It will also look at the volume of injection water needed to sustain and then grow irrigation on the Poverty Bay Flats.
The injection trial started in autumn 2019 when river flows were greater than 4000 l/s. The project team will continue to progress science studies and preliminary site work in the coming months to support the trial and understand potential impacts.
Based on the actual costs incurred during the pilot trial, stage 2 is estimated to cost $1190,000.
Golders International Consultants produced a report on stage one of the trial and did not identify any adverse environmental effects. See report - Results 2017 Injection Trial December 2017
There's a clear distinction between the trial in the Makarui aquifer and any future development of a MAR scheme. Once the trial is completed, Council’s role in any MAR scheme will be regulatory.
The information gained during the trial will be available to any party seeking to develop a MAR scheme.
A company MAR Limited has been set up by horticultural interests, including Mangatu Blocks, Kaiaponi Farms, Leaderbrand and some smaller firms. This group is planning how they can use the findings of the MAR trial for future development.
Gisborne District Council has only committed to the trial to see if it will work.
The Makauri aquifer is the largest underneath the Poverty Bay Flats, extending from Kaiteratahi down to Makaraka and spanning both sides of the Waipaoa River.
The aquifer is an area of gravel and sand under the flats that's saturated with water. It naturally recharges by water percolating from the river and higher aquifers through the gravel into it, a slow process that happens over several decades.
Since the horticultural boom in the 1980s, irrigation of crops has remained at a constant level leading to the decline of the aquifer.
It has very little natural recharge from rainwater and river water because of changes to the land such as flood control, vegetation clearance, rainfall and climate changes.
The Poverty Bay Flats is an area of 18,000 hectares and is the single largest area of highly fertile soil in the country. It's among the most productive horticultural areas thanks to a combination of high sunshine, fertile soils and mild temperatures.
Currently about 1 million cubic metres is taken from the aquifer each year.
Modelling shows that 660,000m3 per year is required to go back in to stabilise the aquifer, with even more required on top of that to enable any expansion of irrigation.
Irrigation would need to be reduced by two thirds of current use to equal natural recharge.