About the Project

New Zealand's water resources are extremely valuable and yet are poorly understood. The national groundwater resource is valued at $8 billion NZD and provides 35% of the nation's consumptive water use, with 80% of this groundwater allocation used for agriculture. As surface water is already fully allocated in many catchments, future consumptive use of groundwater will increase. If the resource is not adequately understood and effectively managed, this might cause spatial or temporal water scarcity situations. Groundwater also provides base flow to rivers, streams, springs and lakes, which are vital to the tourism industry and central to the cultural and recreational values of New Zealanders.

Without essential information related to basic aquifer properties, management decisions have to be made without knowledge of groundwater volumes, flow rates and directions, or extent of interaction with surface water. Better understanding of water resources will lead to improvements in water management with potential to prevent social, cultural, environmental and economic losses. Understandably, central and regional government has identified improved characterisation of groundwater resources as a top research priority.

Objectives

The overall aim of the proposed research is to develop a suite of highly innovative methods for characterising New Zealand’s groundwater systems. Transdisciplinary information needs have been determined by stakeholder consultation and include the measurement of:

  • groundwater volume and changes in it over time
  • aquifer hydraulic properties
  • fluxes of groundwater interchange with surface waters
  • water age.

Overarching research will be undertaken in parallel to communicate these issues effectively by means of

  • uncertainty quantification
  • data synthesis and visualisation

Research programme

Groundwater resources account for one third of New Zealand’s consumptive water needs [1,2]. 80% of these groundwater supplies are used in the agricultural sector [1,2], which is valued at ca. $17 billion (10% of GDP) [3]. Groundwater also supplies the base flow to streams and springs, which are vital to the nation’s tourism industry (valued at ca. $7 billion) [4] and to the cultural, environmental and recreational values of New Zealanders. Reliance on groundwater will increase in the future because surface water is fully allocated in many catchments [1,2].

Despite the importance of New Zealand’s groundwater resources, we still lack essential information related to their basic properties. Information needs to be addressed in this research programme have been determined by stakeholder consultation and include the following:

  • The total volume of groundwater and any temporal changes in this value, both nationally and in individual aquifers, has only been estimated crudely [5,6]. Groundwater volume (storage) is a key term in the water balance equation and this information is crucial for determining whether current allocation limits are sustainable, or to what extent we are “mining” groundwater in some aquifers.
  • Aquifer hydraulic properties have been measured for very few wells. Hydraulic conductivity is a key variable determining groundwater flow rates, but a recent national compilation indicates that it has been robustly measured at only 200 wells [7] (ca. 1% of NZ wells); whilst transmissivity and storativity have been robustly measured at only 2,300 wells (ca. 15% of NZ wells). Without knowledge of an aquifer’s hydraulic properties, it is difficult to reliably construct and interpret groundwater models. It is also difficult to evaluate local or cumulative effects of pumping at the ca. 13,000 wells (ca. 84% of NZ wells) across New Zealand that have consents to abstract groundwater [2] but at which hydraulic properties are unknown.
  • Fluxes across the groundwater-surface water interface are not known. This includes locations and volumes of groundwater recharge from rainfall and groundwater interchange with streams, rivers and lakes. Without this information it is very difficult to manage the water resource holistically.
  • Groundwater age still needs to be determined and refined at the aquifer scale. Without understanding groundwater age, the development of effective management strategies is severely hampered by inability to establish cause-and-effect in terms of aquifer response to human influence.

"Traditional" methods for aquifer mapping and characterisation exist, but they are prohibitively time consuming and too costly for wide scale application. Such methods also generally provide data at very limited spatial and temporal resolution. The traditional method for estimating aquifer volume is to drill boreholes at several locations to establish depth to the basement, ideally in conjunction with some type of active geophysical survey to interpolate the basement surface between boreholes. Hydraulic properties are typically determined by aquifer testing, in which water is pumped from the well of interest while groundwater levels are monitored at nearby bores. Fluxes of water into or out of a stream are typically quantified by concurrent gauging surveys, in which discharge is compared between two stream reaches. Rainfall recharge to aquifers is traditionally measured using paired lysimeters; however, fewer than ten lysimeter stations are in operation in New Zealand, providing extremely poor coverage of the spatial variation of rainfall recharge. Determination of groundwater age at the aquifer scale requires time-series analysis of tracers, e.g. tritium, in multiple wells. Overall, it is reasonable to estimate that national mapping of aquifers using traditional techniques would cost on the order of $20-30 million and require a decade or more to complete.

The overall aim of the Smart Aquifer Characterisation research programme is to assemble and validate a suite of highly innovative techniques that can be applied to map and characterise New Zealand’s aquifers. The SMART (Save Money And Reduce Time) project will place emphasis on techniques that use passive data sources. That is, they rely on existing data sources, or on new measurements that can be made over large areas with little effort and minimal cost. The new methods to be used will be prioritised through stakeholder consultation, but may include ambient noise seismic tomography, airborne geophysical surveying, satellite remote sensing, fibre optic temperature sensing, and novel age tracers (Table 1). Validation will be achieved by the use of multiple methods in case study areas (yet to be selected), and by “ground-truthing” to existing data obtained from traditional methods. Overarching research will be undertaken to develop a consistent objective framework for uncertainty quantification, and a web portal and harmonised 3D groundwater database that will meet stakeholder needs for open access, ease of use, and interoperability with existing systems.

Table 1 – Aquifer properties to be measured and proposed methods to be applied in the Smart Aquifer Characterisation research programme.

SMART applied methods

The research project is led by the GNS Science Hydrogeology team. The programme is led by S Cameron, Senior Hydrogelogist. Other key research leaders from GNS Science include: P White, Z Rawlinson and U Morgenstern, who have several decades of collective experience covering physical/chemical hydrology, 3D geological characterisation of groundwater systems, numerical modelling, geophysics, groundwater-surface water interaction, aquifer hydraulics and water dating. Our research partners provide expertise in key areas: R Westerhoff (Deltares, the Netherlands) in satellite remote sensing; F Verhagen (Royal HaskoningDHV, the Netherlands) in groundwater-surface water interaction; H Klug (University of Salzburg, Austria) in databases and sensor observation services; and N Dudley Ward (Otago Computational Modelling Group, New Zealand) in computational modelling and uncertainty quantification. Our team also includes four co-supervised PhD students. Guidance from a stakeholder advisory panel will ensure that our outputs are of the highest technical calibre while also being relevant and properly structured for rapid end-user uptake. The structure of the research programme personnel is shown in Figure 1.

Figure 1 – Research programme structure. Four of the Research Aims are for over-arching activities; the remaining four are based on methods listed in Table 1. Most Research Aims are co-led by NZ and EU researchers. The programme supports four PhD students co-supervised by NZ and EU researchers.

Methods

Traditional methods for determining these properties exist (e.g. drilling, aquifer testing, river gauging) but we are focusing on novel methods that provide accurate data "passively". New findings rely on existing data sources or on new measurements that can be made over large areas with minimal cost. The methods to be used will be prioritised through stakeholder consultation but may include: ambient noise seismic tomography, airborne geophysical surveying, satellite remote sensing, fibre optic temperature sensing; and novel age tracers. Validation will be achieved by use of multiple methods in case study areas (yet to be selected) and by "ground-truthing" to existing data obtained from traditional methods and in situ Sensor Observation Networks.

References

1. White PA (2001). Groundwater resources in New Zealand. In: Rosen, M.R. and White, P.A. (eds.) Groundwaters of New Zealand, New Zealand Hydrological Society, Wellington, New Zealand: 47-75.

2. Rajanayaka C, Donaggio J, McEwan H. (2010). Update of water allocation and estimates of actual water use of consented takes – 2009-2010. Aqualinc Research Report H10002/3.

3. Statistics New Zealand (2010). National accounts: Year ended 2010. www.stats.govt.nz.

4. Statistics New Zealand (2010). Tourism satellite account. www.stats.govt.nz.

5. White PA, Reeves RR (2002). The volume of groundwater in New Zealand 1994 to 2001. GNS Science Client Report 2002/79.

6. White PA (2007). New Zealand groundwater volumes – Update for June 2005. Unpublished letter report to Statistics New Zealand.

7. Meilhac C, Cameron S, Minni G (2010). Compilation of aquifer test data for sites in the National Groundwater Monitoring Programme. GNS Science Report 2009/19