Inverting electromagnetics – a new way to measure groundwater flow

Photo of Whanganui River

A team of SfTI researchers have developed electromagnetic sensors that for the first time could allow water resource managers to accurately measure the volume and flow of groundwater.

Snapshot

  • This technology will help tackle issues of groundwater contamination and the preservation of precious water resources as parts of the world suffer the effects of climate change.
  • The project has progressed well, with a lab-scale prototype of the technology in operation and significant improvements achieved in magnet and sensing technology that will underpin the sensors.
  • The next phase will see field trials of the technology and partnerships with New Zealand tech companies with a view to preparing the sensors for commercial use.
 

Diagram illustrating the percentage of the Earth's ground water 

Getting a sense of our precious groundwater resources.

Groundwater that lies beneath tens of thousands of square kilometres of Aotearoa represents one of our most precious natural resources. The water feeds rivers and lakes and is also used for town and city supplies, agriculture and industry. It is mostly derived from rain that travels near the ground surface or deeper in aquifers, fed from water that has seeped through the Earth’s surface over thousands of years, forced by gravity into crevices underground.

While we know well how important groundwater is to our natural environment and for human uses, we still lack the tools to efficiently monitor the health of our groundwater and hard to reach aquifers.

Helping tackle climate change

The Spearhead team, headed by Lincoln Agritech’s Professor Ian Woodhead and featuring experienced scientists from across our universities and GNS Science, are developing electromagnetic sensors that could for the first time allow researchers to peek at groundwater and also determine flow into aquifers.

Commercialising the technology has serious potential for New Zealand with governments and water authorities the world over struggling to get to grips with how to measure and manage groundwater resources as they face the impacts of groundwater contamination, climate change and more frequent droughts.

Underground sensing - how does it work?

The researchers have developed a novel groundwater sensor, based on the age-old Faraday effect[1]that detects miniscule signals induced by the slow-moving groundwater. This new technique allows the sensor to detect and quantify sources of water, its speed and direction.

The science around the sensor is very challenging, but there are no alternatives that avoid small scale variations yet can measure the very small speeds to accurately gauge groundwater flow velocity. Our groundwater is frequently threatened with contaminants, but accurate measurement poses particular challenges and researchers tackling the issue have been constrained by limited information on groundwater flow.

 

Diagram illustrating the Faraday effect

Making sensors cost effective and accessible

The ultimate outcome is sensor technology that is minimally invasive and can be deployed cheaply so that local authorities can monitor the flow of groundwater to preserve the resource and limit its contamination with pollutants.

The project is drawing on fundamental science to overcome some major challenges that have now been largely cracked. The sensing technology requires precise manipulation of large-scale magnetic fields and very accurate detection of electromagnetic signals, while compensating for the background electrical noise that might muddy the picture.

The team is also working on ways to visualise the data and merge it with other layers of data so it is of immediate use to water quality managers. It is a complex problem, but one New Zealand researchers involved in the project think they have the answer to.

 

 

Lab-scale model of an aquifer from the lab at Lincoln Agritech

The team

  • Spearhead Leader, Professor Ian Woodhead – Lincoln University, Chief Scientist and Lincoln Agritech Technology Group Manager
  • Emeritus Professor John Talbot Boys, University of Auckland
  • Professor Bob Buckley – Victoria University of Wellington
  • Dr. Nick Long – Victoria University
  • Dr. John Kennedy - GNS Science
  • Associate Professor, Michael Hayes – University of Canterbury
  • Dr Ian Platt – Lincoln Agritech
  • Associate Professor, Colin Fox – University of Otago
  • Associate Professor, Maui Hudson – University of Waikato

Top image: Whanganui River

[1] Faraday’s Law of Induction describes how an electric current produces a magnetic field and, conversely, how a changing magnetic field generates an electric current in a conductor. Source: https://www.livescience.com/53509-faradays-law-induction.html