3D Aquifer Mapping Project FAQs

We are using the latest airborne electromagnetic survey technology (SkyTEM) to see deep underground and get a picture of our aquifers that we’ve never had before. You may see a helicopter towing a large hoop hanging from a cable which ‘scans’ the aquifers. The information we get from this will help us to get a 3D picture of what the aquifers look like down to 300 metres underground.

This is a big step forward for the Hawke’s Bay community in getting better understanding of our water resource.

SkyTEM technology is widely accepted globally as the best method for mapping water resources. It is the ‘rolls royce’ of aquifer mapping. Its advanced technology is a safe and cost effective way for the Regional Council to get precision imaging.

Water storage, access and security is an important focus for the Hawke’s Bay Regional Council, iwi, local authorities, industry bodies and communities. As a region, we understand a combined/collaborative approach is needed to protect, predict and manage this resource for future generations.

We are building a crystal clear understanding of our region’s water supply and gaining cutting edge understanding of the region’s major aquifer systems.

It will give us cutting-edge scientific information to understand what’s happening underground in our aquifers and fill the gaps in our knowledge.

We can literally have a look down to 300 metres deep underground – including at depths previously unexplored. It will also give us high-resolution information of the shallow system, which is critical for managing groundwater/surface water interaction, drinking water supply risks and shallow groundwater resources.

Korus J. 2018. Combining Hydraulic Head Analysis with Airborne Electromagnetics to Detect and Map Impermeable Aquifer Boundaries. Water. 10(8):975. doi:10.3390/w10080975.

Our current knowledge of the aquifer systems has come from drilling logs, collected for example when a bore for extracting groundwater is developed, and water sampling from such bores. Most of our bores are less than 50 m deep, and little is known about properties of deeper aquifer systems.

The 3D aquifer mapping project will significantly advance the Regional Council’s ability to holistically image and characterise major aquifers at system-wide scales and depths, with the resolution needed for local understanding.

There’s more information about our aquifers here

Our Hawke’s Bay aquifers provide groundwater that we use for drinking, agriculture, horticulture, industry and the environment.

There are nine productive aquifer systems in Hawke’s Bay, two large – Heretaunga, Ruataniwha – and seven smaller - Mahia, Nuhaka, Wairoa, Esk, Poukawa, Papanui/Otane, Waipukurau/Waipawa.

Groundwater is the water found underground in the cracks and spaces in soil, sand and rock. It is stored in and moves slowly through geologic formations of soil, sand and rocks called aquifers.

The SkyTEM airborne electromagnetic survey technology was developed by the Danish Government and Universities specifically for efficient and effective mapping of groundwater resources.

The technology has been used commercially since 2004 to map large aquifer systems in countries including Denmark, Netherlands, India, USA, Canada and Australia. SkyTEM technology can map the subtle changes between sand, clay, silt, gravel and tills that define the location and potential vulnerability of groundwater resources. 

Check out more information about SkyTEM here

The photo below shows what the SkyTEM helicopter and aparatus look like. The helicopter will fly at 80-100 km/hr in parallel lines 200 m apart and at a height of approximately 100 m. The measurement instruments are suspended under the helicopter and will be about 35 m above the ground.     

The Regional Council’s Head of Science, Dr Jeff Smith, says there’s limited exposure to the magnetic field generated from airborne SkyTEM equipment as the system is being flown at high speed. It’s comparable to standing 0.2 metres in front of your house, and safer than watching a LCD or plasma TV or blow-drying your hair!

The noise from the helicopter has been described as the equivalent to a truck going past on a motorway, and lasts for around two to four minutes. The helicopter flies up and down in gridlines, so it will then return approximately 30 minutes later but be 200 metres away.

The SkyTEM team says most stock are unfazed by the helicopter, but younger stock could be more of a problem. When SkyTEM was used in the Waikato horses were observed during the flyover in the Piako catchment and they continued grazing happily.

If you are concerned about the effect helicopter flights might have on you or your stock (particularly horses) email 3Dwater@hbrc.govt.nz or phone (06) 835 9200 and ask for the 3D water team. We can let you know flight details. Alternatively, we will be keeping our website and facebook page updated daily with flight information.

The Regional Council, in partnership with the Provincial Growth Fund (PGF) and GNS Science, is spending money on tried and true, cutting edge Danish technology that has been used extensively overseas

The total cost for the project is $4.3 million dollars. It’s a joint effort with the PGF contributing $2.15 million, the Regional Council $1.85 million and GNS Science assisting with $300,000.

Water management is crucially important for the future of our region. The more information we have about our aquifers, the better our decision making can be.

GNS Science is working closely with the Regional Council on the 3D aquifer mapping project and have committed $300,000 to the project through their Groundwater Strategic Science Investment Fund (SSIF) Research Programme. This is because the work programme is highly relevant to current research at GNS Science on advancing our understanding of NZ’s aquifers through cutting-edge measurements, mapping, and modelling of our aquifer systems.

GNS Science is strongly committed to achieving the objectives of the collaboration - to provide robust scientific data to further enable sustainable resource management in the Hawke’s Bay region. Internationally, similar initiatives have resulted in significant advances in the understanding, mapping and modelling of aquifer systems.

The Provincial Development Unit has $3 billion to spend over three years to reinvigorate regional New Zealand. This investment will create jobs, improve wellbeing, increase environmental sustainability, create better road and digital connections and diversify the economy. 

The Hawke’s Bay was identified early on as one of six ‘surge regions’, in need of early and prioritised investment. Among other investments, a package of $68 million was announced for the region, relating to skills and employment, Hawke’s Bay Airport, transport and water storage. 

The Regional Council is responsible for making decisions about our water and how we use it. The information will help us better understand our aquifers and our groundwater, to protect and manage this resource for future generations.

These flights are not in any way used for compliance monitoring.

The results from the 3D aquifer mapping will be a big asset to the Hawke’s Bay community, and freely shared and available to tangata whenua, other councils and groups. We will let the public know when they are ready.

If you would like to join our mailing list for updates please email your details to 3Dwater@hbrc.govt.nz.

The SkyTEM helicopter will fly over the blue coloured areas on the maps below and ‘scan’ them. The areas are;

- Heretaunga Plains and offshore

- Ruataniwha Plains

- Otane and Poukawa Basins

- Ngaruoro River Valley

We won’t be flying over built up urban areas like Napier, Hastings and Havelock as the high presence of steel in buildings and infrastructure disturbs the electromagnetic response of the SkyTEM technology.

The first map below shows the total area which will be surveyed by the SkyTEM helicopter. More detailed maps of each individual area follow.

The helicopter will fly at 80-100 km/hr in parallel lines 200 m apart and at a height of approximately 100 m. The measurement instruments are suspended under the helicopter and will be about 35 m above the ground.

The 3D aquifer mapping project will start around 20 January 2020 and will take about six weeks, so should finish in early March. Keep an eye on our website and facebook page and listen to local radio stations for updates around that time.

The SkyTEM system is an airborne transient electromagnetic system. The system uses a magnetic field to generate an electric current in the subsurface (an eddy current) and then measures the behaviour of that induced electric current. Such measurements can be used to infer subsurface properties relevant to understanding groundwater resources.

As rocks are composed mostly of silicate minerals that are essentially insulators, electrical conduction is dominated by electrolytic conduction, and depends mainly upon porosity, permeability, moisture content, concentration of dissolved electrolytes, temperature and phase of pore fluid, and amount and composition of clay content.

Groundwater acts as an electrolyte, and so increases the conductivity of water-bearing lithologies. This conductivity increase depends on the volume of water as well as the chemical composition of the water. Fresh water is resistive, but contaminants such as clays and/or salt will increase its conductivity.

The SkyTEM survey will deliver:

- precise 3D hydrogeological models for entire aquifer systems (see Figure 1 for an example) and, consequently, greatly improved conceptual understanding of aquifer systems and variability of aquifer properties;
- improving the reliability of groundwater flow modelling predictions, including at small spatial scales;
- enhancing understanding of groundwater and surface water interaction;
- exploring the extent of deep groundwater resources and aquifer properties;
- precise identification of boundaries that define groundwater recharge areas, confined aquifers and semi-confined areas;
- identifying areas of vulnerability to contamination from land use activities and discharges to groundwater; and significantly reducing the uncertainty of groundwater transport modelling predictions that are sensitive to small scale variability, such as pathogen transport. This will be particularly valuable for identifying source protection areas based on risks of pathogen contamination to drinking water supplies.

Figure 1. Example of a 3D geological model developed using SkyTEM data and bore log information.

Along with being a powerful visualization tool, this model is ready for application in a groundwater flow model, such as MODFLOW.

Figure from Korus (2018)

The Heretaunga and Ruataniwha surveys will deliver electromagnetic data every ~11 metres along transects approximately 200 metres apart, to depths of approximately 300 metres. Figures 2 and 3 show the preliminary SkyTEM flight paths for the Heretaunga and Ruataniwha surveys, along with the locations of wells greater than 50 metres depth. There are very large distances between wells in areas with demand for groundwater resources and, with known variability within these aquifer systems, SkyTEM will provide far greater certainty of aquifer properties throughout these areas.

Figure 2. Heretaunga Plains Survey - SkyTEM Flight Paths (green lines) and location of wells greater than 50 m depth (blue circles).

Figure 3. Ruataniwha Survey - SkyTEM Flight Paths (green lines) and location of wells greater than 50 m depth (blue circles)

To illustrate the value of electromagnetic surveys, Figure 3 shows the poor knowledge gained from 518 drilling logs in an area of Denmark, compared with the outcome from a ground-based electromagnetic survey with 1400 TEM soundings (ground-based equipment that is directly equivalent to skyTEM). The conceptual understanding of aquifer structures was significantly different after the ground-based TEM survey, which was subsequently verified by new boreholes. The TEM survey also revealed completely unknown aquifers in the area. For regional scale mapping, SkyTEM is much more cost effective, provides significantly more soundings, and delivers more accurate data than these ground-based surveys.

Figure 4. Comparison of borehole and ground-based TEM mapping in an area of Denmark. The dark blue areas are thick aquifers, while red colours show areas with no aquifer or a thin aquifer.

Reference

Rethink Water & Danish Water Forum. 2013. Groundwater mapping and sustainable groundwater management. White Paper. http://skytem.com/wp-content/uploads/2014/12/Greater-water-security-with-groundwater.pdf.

Following the airborne surveys, electromagnetic data will then be processed to provide a resistivity model for each transect throughout the survey area. An example is shown in Figure 5.

Figure 5. Example inversion showing resistivities at depths to 500 m below ground level.

A similar model is produced for each transect, which may then be interpreted collectively along with borehole data to produce a 3D geological model for visualization of entire aquifer systems. As an example, slices through a 3D geological model for an aquifer system in Denmark are shown in Figure 6.

Figure 6. Slices through a 3D geological model constructed using SkyTEM data and information from boreholes.

The data are also particularly valuable for informing groundwater flow and transport models that are used for water resource management. One example of this application is shown in Figure 7, where a clay fraction model is created. This clay fraction model was subsequently utilized to inform aquifer properties within a groundwater flow model ­– as clay content is related to aquifer properties such as hydraulic conductivity.

It can be seen that significantly more variability of aquifer properties is able to be mapped by utilizing the skyTEM data compared to utilizing boreholes alone (Figure 7c-d). This enables water resource management to be more fully informed by the groundwater models, and to reduce the uncertainty of decisions informed by such models.

The Hawke’s Bay SkyTEM surveys will deliver information in great detail and will generate substantially more knowledge than we currently have on the region’s major aquifer systems.

Figure 7. a) Interpolated resistivity horizontal slice at 2 m below sea level. b) Clay Fraction model corresponding to the resistivity shown in a). c) Resistivity cross-section (grey line in a)) with boreholes within 200 m of the profile superimposed: black blocks mark clay layers and yellow blocks mark sand and gravel layers. d) Clay fraction cross-section (grey line in b)) with the same boreholes as plotted in c).

References

Foged N, Marker PA, Christansen AV, Bauer-Gottwein P, Jørgensen F, Høyer A-S, Auken E. 2014. Large-scale 3-D modeling by integration of resistivity models and borehole data through inversion. Hydrology and Earth System Sciences 18(11):4349–4362. doi:10.5194/hess-18-4349-2014.

Høyer A-S, Jørgensen F, Foged N, He X, Christiansen AV. 2015. Three-dimensional geological modelling of AEM resistivity data — A comparison of three methods. Journal of Applied Geophysics. 115:65–78. doi:10.1016/j.jappgeo.2015.02.005.

If you are interested in updates from us on the results of the 3D aquifer mapping project, please email us at 3Dwater@hbrc.govt.nz to be added to our database.

The Regional Council would like to thank Lincoln Agritech for sharing information, photos and videos of its SkyTEM experience.

Lincoln Agritech and its MBIE-funded Critical Pathways Programme applied the SkyTEM technology to NZ early in 2019.

The team mapped the shallow subsurface in the Piako headwater and Waiotapu Stream catchments to research how water and nutrients move from the land into a waterway.

An introduction to their research programme can be found in:

Stenger et al (2019) Critical Pathways Programme: unravelling sub-catchment scale nitrogen delivery to waterways. In: Nutrient loss mitigations for compliance in agriculture. (Eds L. D. Currie and C. L. Christensen). https://researcharchive.lincoln.ac.nz/bitstream/handle/10182/11724/FLRC_auditing_2019.pdf?sequence=3&isAllowed=y. Occasional Report No. 32. Fertilizer and Lime Research Centre, Massey University, Palmerston North, New Zealand. 

The pdf of the manuscript can be downloaded here (free of charge)

For more information please contact Roland Stenger phone (07) 858 4844 at Lincoln Agritech.

We would love to hear from you with any questions you may have. Find out the ways you can contact us here.

The results from the 3D aquifer mapping will be a big asset to the Hawke’s Bay community, and freely shared and available to tangata whenua, other councils, researchers  and groups. We will let the public know when they are ready.

If you would like to join our mailing list for updates please email your details to 3Dwater@hbrc.govt.nz

We are not flying over Napier, Hastings and Havelock North for the 3D aquifer mapping survey, because the high presence of steel in buildings and infrastructure in urban areas disturbs the electromagnetic response of the SkyTEM technology. This affects the data collection.

However, there may be opportunities for us to use similar ground based methods in these dense urban areas to provide underground images.

We have envisaged that ground-based work would be key to getting a full picture of the larger urban areas once the SkyTEM models had been completed.

The Regional Council decided not to include Wairoa aquifers in the 3D aquifer mapping survey as there is already good information of what the aquifer systems there are like – they are generally shallow and sandy with some gravel.