New Zealand’s Poverty Bay Flat/Tūranganui-ā-Kiwa in the Gisborne district is home to a thriving horticulture industry which relies heavily on irrigation water sourced from aquifers and surface water. Concerns about over-abstraction and long-term decline in aquifer water levels motivated the Gisborne District Council (GDC) in 2014 to research whether the decline in groundwater levels could be reversed via Managed Aquifer Recharge (MAR).
More recently, Golder identified changes to groundwater quality and increased salinity trends in various water supply wells across the Poverty Bay Flat, underscoring the need to better manage the local fresh groundwater resource. In May 2017, GDC commissioned the first injection trial as part of the Gisborne MAR project to investigate the feasibility of MAR to provide a water management solution that would benefit the wider community and environment. The project was made possible by funding from the Provincial Development Unit.
Golder has been involved since 2014 as a technical lead in the initial hydrogeology investigations and in the 2017–2020 injection trials. Golder helped to significantly improve the understanding of the aquifer system and dynamics and presented this in several stakeholder engagement meetings.
In the first injection trial during the winter of 2017, a total of 73,180 m3 of water from the Waipaoa River was injected after filtering into the Makauri aquifer with a single injection well over a period of three months. Some hydrogeochemical processes could not be adequately monitored during the first trial due to the limited number of monitoring wells, and concerns remained about potential effects on water quality and well clogging. To investigate this, a second injection trial ran from August to October 2019 with 39,881 m3 injected and included ongoing monitoring across four new monitoring wells within and outside the injection plume. A third trial ran from May to October 2020 with 104,557 m3 injected.
Each trial achieved a clear rise in aquifer water levels, suggesting that the long-term downward trend could be reversed if MAR is deployed at full scale permanently. Ongoing monitoring shows no indication of adverse groundwater quality effects from MAR. The river water injection improves the Makauri aquifer water quality by making it fresher and less corrosive than ambient groundwater.
Golder collaborated with the Netherland’s KWR Water Research Institute since 2017 to develop the monitoring program, review the MAR infrastructure and procedures, assess the occurrence of adverse water quality effects through monitoring, and investigate ongoing well clogging. We also monitored well performance, analysed ongoing pumping testing results and advised on well operation and maintenance. Golder was instrumental in optimising the injection system design and semi-automation, which helped improve injection well performance.
In addition, Golder’s innovation fund provided in-kind support to the project through the development of a catchment-wide comprehensive geological model and numerical groundwater model, and used this to assess injection plume migration, long-term effects on groundwater levels and the quality of different full-scale MAR scenarios.
By improving aquifer yield and groundwater quality, the Gisborne MAR project will benefit the community and the catchment by improving water security for many stakeholders. Opportunities can be explored to assess other potential environmental benefits such as enhancing base flow and water quality in streams and wetlands. The project may even enable expansion of the total area of productive land that can be irrigated sustainably.
MAR is a relatively new concept for New Zealand with only a few projects currently being developed. However, internationally, MAR has been a highly successful technology in providing safe and clean water to communities and industries at a large scale, particularly in Europe and the USA. New Zealand’s abundance of surface water and good aquifers offer many opportunities to utilise MAR to help achieve a sustainable management of water resources.