Researchers find low-cost, sustainable way to explore groundwater

A collaborative team of water engineers has developed a new technique to investigate and manage groundwater resources. The passive exploration method allows for more sustainable groundwater analysis at lower cost compared with current techniques.

In an article to be published in Reviews of Geophysics, the research team from UNSW Sydney, Karlsruhe Institute of Technology (KIT) in Germany and Deakin University details how changes in groundwater levels caused by the effects of Earth and atmospheric tides can be measured via monitoring boreholes.

Dr Gabriel Rau, an engineering geologist at KIT affiliated with UNSW’s Connected Waters Initiative (CWI) Research Centre, described the new method as paradigm shifting.

“We can use the impact of Earth and atmospheric tides on commonly acquired atmospheric and groundwater pressure to obtain unprecedented knowledge of subsurface properties at low cost,” he said.

“Similar to tides in the ocean, the groundwater level is affected by tidal forces squeezing the porous rocks in the subsurface and causing measurable pressure changes.”

Dr Rau explained that current testing methods require active pumping of water from a specially designed water-extraction well and observing the water level response in other wells in the vicinity. This strategy is expensive and only provides a result for a particular location. A crew of two to three people managing the drill rig to pump water out is also needed, with the process taking a few days up to several months.

“The properties of groundwater reservoirs — also known as aquifers — vary greatly in space, and it is much too expensive and intrusive to build extraction wells everywhere,” he said.

“The new method, on the other hand, involves using tidal information embedded in water levels from monitoring boreholes. It is a passive technique and simpler to conduct than the current practices of pump and aquifer testing.”

The passive approach requires only a small hole to be drilled, then an automated water pressure data logger is placed in the hole for a month, which produces the same results.

Co-author Timothy McMillan, from the UNSW CWI Research Centre and School of Minerals and Energy Resources Engineering, said, “An added advantage of our new approach lies in the fact that we can re-analyse decades of existing water level data to calculate subsurface properties that change over time.”

The global increase in groundwater extraction is linked to falling water tables, ground surface subsidence, water quality degradation and reduction of stream baseflow. It is hoped that knowledge of the impact of Earth and atmospheric tides on groundwater can be used to forecast the effect of climate variability on groundwater resources.

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