Hawke’s Bay 3D Aquifer Mapping (3DAMP)

Overview

GNS Science and Hawke’s Bay Regional Council partnered on the largest-scale groundwater mapping project ever done in New Zealand. The Hawke’s Bay 3D Aquifer Mapping Project (3DAMP) is a four-year initiative (2019–2023) jointly funded by the Provincial Growth Fund, Hawke’s Bay Regional Council and GNS’ Groundwater Strategic Science Investment Fund (SSIF) research programme.

The 3DAMP project aims to deliver a significant advancement in the detailed understanding of the region’s underground freshwater resources and enable more effective management of these resources. It will also advance our ability to map aquifers from local to national scale and provide decision-making tools that could be used by councils all over New Zealand.

The project applies SkyTEM technology to improve mapping and modelling of groundwater resources specifically within the Heretaunga Plains, Ruataniwha Plains and Poukawa and Otane basins. 3DAMP involves collaboration between HBRC, GNS and the Aarhus University HydroGeophysics Group.

The SkyTEM system was developed by the Aarhus University HydroGeophysics Group in Denmark. It is a geophysical technique that uses electromagnetic waves to investigate the shallow (up to 500 m) resistivity structure of the earth.

Close to 8,000 line km of data were collected in Jan/Feb 2020 by SkyTEM Australia Pty Ltd. using a helicopter equipped with a SkyTEM system.

Using these data, electrical resistivity models of the three areas have been developed. The subsequent development of hydrogeological models is currently underway.

To achieve these objectives

• SkyTEM data was collected across the Ruataniwha Plains, Heretaunga Plains and the Poukawa and Otane Basins
• pre-existing supporting data was compiled and assessed, and some additional data was collected through a drilling programme
• the SkyTEM data was processed and resistivity models developed
• the resistivity models are being analysed alongside the supporting datasets, and hydrogeological models are being developed
• the Hawke's Bay Regional Council’s numerical groundwater models in the Heretaunga Plains are being updated with these data
• the developed models will be made publicly accessible through online tools. Access to models in the Poukawa and Otane survey area have been made available here.(external link)

The project

Why use airborne electromagnetic data?

Traditional methods of gathering data from drilling or ground-based surveys are slow, costly, provide poor spatial data coverage, and generally don’t go deep enough.

Aerial mapping, on the other hand, can cover large areas of ground quickly and cost-effectively, giving high levels of detail on the subsurface. Developed by Aarhus University in Denmark, SkyTEM provides a 3D view of the subsurface to about 500 m (depending on the noise and geology). In comparison, most available information from boreholes within the Heretaunga Plains is within the upper 50 m.  

SkyTEM is an airborne dual-moment time-domain electromagnetic survey technology. Electromagnetic (EM) data is sensitive to rock type, porosity, permeability, clay content, moisture content, and properties of the water. These all help in understanding and mapping aquifers.

Adding more to the picture

Data was collected in January and February 2020. A drilling programme was undertaken in 2021 to collect additional data to support hydrogeological interpretations.

Through 2020 – 2022, GNS processed the SkyTEM data, primarily to remove EM noise, and developed electrical resistivity models. GNS is currently working on hydrogeological interpretations of these data and numerical groundwater modelling in the Heretaunga Plains.

GNS is also currently working with HBRC to develop an online interface to provide easy access to the 3D models being developed. A first release(external link) was made available in June 2022, and subsequent releases are planned in 2023.