The Gisborne District Council (GDC) has identified long term water availability in the Poverty Bay area as being a potentially limiting factor in future regional development. A substantial proportion of the water used for irrigation across the Poverty Bay Flats is derived from groundwater. Reviews of groundwater levels in the Poverty Bay Flats area have identified declining groundwater pressure trends as an environmental and water supply issue. These trends are linked to increasing groundwater abstraction for irrigation purposes.
The GDC is investigating water management options to stabilize groundwater pressure trends and increase water supply reliability in the Poverty Bay area. One option under investigation is the use of Managed Aquifer Recharge (MAR), to replenish and sustain groundwater yields from aquifers beneath the Poverty Bay Flats. Golder Associates (NZ) Limited (Golder) was commissioned by GDC to undertake a feasibility assessment for a MAR program.
The MAR feasibility assessment carried out by Golder included an evaluation of the challenges and needs for Poverty Bay water management, including source water options, direct injection and surface infiltration options and water quality management requirements.
A Groundwater Management Tool (GMT), incorporating a calibrated water balance model for the Makauri Aquifer, has been developed to a demonstration stage for the GDC using the Goldsim software package. The GMT is intended to support the GDC in assessing options for the management and replenishment of the Poverty Bay Flats groundwater supplies, within the framework of water management planning for the region.
Golder’s feasibility analysis shows a groundwater replenishment scheme has the potential to:
- Stabilise current downward trends in groundwater levels within the Makauri Aquifer
- Restore groundwater pressures within the aquifer
- Enable the establishment of a sustainable yield for the aquifer that exceeds current usage
In summary, Managed Aquifer Recharge (MAR) has the potential to replenish and support sustainable groundwater yields from aquifers beneath the Poverty Bay Flats. The results from a risk-benefits analysis indicate that the further Stage II analysis, design and costing for a pilot injection MAR site is recommended.
Report Submitted to Gisborne District Council, New Zealand, August 2014.