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Thirlmere Lakes research shared with local community

Thirlmere Lakes, situated in the Greater Blue Mountains World Heritage Area in NSW, are thought to be about 15 million years old.

Published on the 09 November 2021
Conceptual hydrogeological model of Lake Baraba and Lake Couridjah indicating the hydraulic situation of May 2019. Hydraulically conductive layers (i.e. sand which allows easy travel of water if present) are displayed in yellow, while unconductive silt/clay layers (which form a barrier for water flow) are shown in grey and peat layers in the lakes are shown in brown. During May 2019 the more elevated Lake Baraba contains water while the lower Lake Couridjah is dry. This indicates that there is no hydraulic connection between the two lakes. Two bores, while drilled to different depths, show a similar groundwater level, indicating a possible regional aquifer spanning below the two lakes, but being hydraulically disconnected from both by the clay, silt and peat.

Thirlmere Lakes, situated in the Greater Blue Mountains World Heritage Area in NSW, are thought to be about 15 million years old. The group of lakes - which includes Lake Gandangarra, Lake Werri Berri, Lake Couridjah, Lake Baraba and Lake Nerrigorang - began experiencing a significant decline in water levels in the last decade, leading to widespread community concern. In 2016, the Department of Planning, Industry and Environment (formerly Office of Environment and Heritage) committed $1.9 million over 4 years to the Thirlmere Lakes Research Program to help understand the fluctuating water levels in the lakes.

UNSW partnered with the Department of Planning, Industry and Environment (DPIE), the University of Wollongong (UoW) and the Australian Nuclear Science and Technology Organisation (ANSTO) to investigate the geology, geomorphology, hydrogeology and hydrology of the system, with the objective of providing a more detailed understanding of the dynamics of water sources and water flows.
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Lake dynamics under the microscope

In addition to looking at the internal dynamics of the system, researchers investigated the sensitivity of the wetland systems to external influences including mining activity and groundwater extraction.

Five research themes were addressed, led by technical experts from each of the project partners. Associate Professor Martin Andersen from the UNSW Water Research Laboratory (WRL) and Connected Waters Initiative (CWI) led two research projects; the first on surface water - groundwater interactions and the second on geological mapping and geophysical surveys of the area. Associate Professor William Glamore (WRL) also played a key role by leading research to develop an understanding of the overall of water balance of the lakes. Research on environmental isotope investigations into periodic and recent water losses from Thirlmere Lakes was led by ANSTO’s Dr Dioni Cendon while research on geomorphology, sub-surface characteristics and the prehistoric environment of Thirlmere Lakes was led by UoW’s Dr Tim Cohen.

Outcomes shared during community science day

At a community science day on 6 June 2021, partners had the opportunity to share their findings and project outcomes with stakeholders and residents from the surrounding area. Around 50 people gathered at the Picton Bowling Club to hear a series of short talks from the researchers.

A/Prof Martin Andersen, Prof Wendy Timms (Deakin University), Dr Timothy McMillan (CWI and School of Minerals and Resources Engineering), Dr Katarina David (CWI and School of Minerals and Resources Engineering), and Titus Murray (Southern Highlands Structural Geology) began the morning’s presentations by sharing the results of their research on geology, hydrogeology and geological structures of Thirlmere Lakes. They discussed the research undertaken and revealed that geological mapping of Thirlmere Lakes National Park did not present any evidence that the lakes were directly impacted by the effects of mining through hydrogeological processes.
Baraba Lake, Thirlmere Lakes region 3 in 2019. Photo by Fang Bian (WRL) UNSW

A/Prof Martin Andersen, Dr Kirsten Cowley, Dr Christian Anibas (WRL) and Dr Gabriel Rau (Karlsruhe Institute of Technology, Germany) then presented the outcomes of their work on shallow groundwater - surface water interactions. Based on an analysis of data from their network of monitoring bores they revealed that the lakes had variable but low connectivity to groundwater, with some lakes experiencing a small groundwater loss. With falling lake water levels, they observed that the downward flow is likely to be decreasing as the surface water gets confined to areas over low-permeable material in the lake beds such as peat and clay.

A/Prof William Glamore (WRL) and A/Prof Fiona Johnson (WRC) then presented their research on current and future climate drivers. They developed detailed surface water balance models for each of the five lakes and considered climate change impacts to understand plausible future changes in the system. Their assessment of the models concluded that a majority of the water losses from the lakes during the major drying period of the study could be attributed to evaporation and transpiration from vegetation. Based on an analysis of past climate data they also concluded that similar dry periods were likely to have happened in approximately the last 100 years. 

Core and drill hole data gathered by UoW researchers revealed that the modern Thirlmere lakes attained their current state 12,000 years ago and that the lakes completely dried 21,000 to 12,000 years ago. Prior to this last major drying period, Thirlmere lakes had a long history of permanent water.

Dr Dioni Cendon, Dr Cath Hughes and Dr Mark Peterson from ANSTO found that evaporation and transpiration dominated losses across all lakes during the major recent drying period of the study, but that a significant component of loss still occurred from each lake to groundwater. They suggested that possible lake management responses could include limiting the increasing regional drawdown of groundwater from multiple sources.

A/Prof Martin Andersen said that the project outcomes were significant for many reasons.

“The collective learnings from the five projects have brought us a much deeper understanding about how the lakes function and the major divers of their water balance and their connectivity to the subsurface,” said Dr Andersen.

“The project has also given us important baseline data, which can be used to assess potential future impacts and inform science-based management. This is very important as our water resources and natural environments, exemplified by these unique and beautify wetlands, are facing multiple threats and competing interests from urbanisation, agriculture, mining and climate change. We can’t manage these systems sustainably without proper process understanding and good monitoring data.”

For further information contact:

Martin Andersen | Associate Professor | m.andersen@wrl.unsw.edu.au