Water temperature to measure groundwater levels

Scientists at the National Centre for Groundwater Research and Training (NCGRT) are using heat to measure the extent to which some of Australia’s inland rivers and streams could dry up due to over extraction of groundwater.

By measuring water temperature both above and below the surface - indicating the rate at which the warmer surface water trickles into the cooler groundwater - “we can gain an idea of how quickly or slowly an aquifer is being recharged,” said Dr Martin Andersen of NCGRT and the University of NSW.

Dr Anderson explained that data loggers have been installed above and below ground around the Murray-Darling Basin, recording temperature changes throughout the day. The natural changes in heat are easy to measure and the loggers can collect data for many years, which “not only helps us build up a consistent picture of water flow in a given area but also means that we can monitor how groundwater levels recharge during floods,” said Dr Andersen.

This data provides information about the connection and flow between different water sources, helping the researchers to test and improve their models. This is especially important given that, according to Dr Anderson, “around 95% of Australia’s total freshwater supplies are underground” and there are “no easy ways to observe the movement and renewability of this water.”

Back in the laboratory, the researchers are using ‘sand tanks’ to test the rate at which water can move between an aquifer and a surface water body. Dr Anderson explained that water “typically penetrates gravels and sands much more readily than it does finer silts and clays,” so its movements could vary between different sections of the same river. The sand tank allows the researchers to examine the movement of water through different materials at different times of the day.

NCGRT Managing Director Professor Craig Simmons noted the importance of the groundwater research, saying increasing extraction “poses a long-term risk as we generally do not know what effect its removal will have on watercourses at the surface, such as streams and rivers.”

“In order to manage this risk, we need to understand how withdrawing water from one area will affect a water source in another,” he said. “Using heat to trace water movement is one important method that we have at our disposal to better understand and manage catchment areas such as the Murray-Darling Basin that provide critical sources of water to communities, businesses and ecosystems throughout Australia.”