Will the rivers run dry?

Understanding how decreasing rainfall is impacting river regions in South-Western Australia.

By Georgia Barrington-Smith & Dr Rebecca Duncan

Global rainfall patterns are changing, leading to dryer conditions in numerous biodiversity hotspots. Rivers in the Southern Hemisphere are particularly sensitive to these climate-induced changes.

To mitigate biodiversity loss and manage our precious water resources, we need to better understand the impacts of changing rainfall patterns on river systems. Specifically, we need to understand whether rivers can buffer or modulate changes in streamflow under a drying climate. The key to unlocking this puzzle lies in determining how surface water and groundwater interact to govern streamflow patterns in river systems.

Rose-Anne’s river investigations

Previous studies in how rainfall affects streamflow patterns in the South-West Australian region have not yet addressed variability in streamflow, arising from storage and release of water, or other hydrological processes.

With this gap in mind, Rose-Anne Bell, AINSE PGRA scholar and University of Western Australia student, has collaborated with ANSTO to investigate the streamflow response in the Donnelly Catchment in the south-western tip of Australia, approximately 250 km south of Perth. This catchment has been drying for several decades, with local rainfall reducing by 15-20% since the 1970s.

Rose-Anne and her collaborators investigated the streamflow response of three adjacent sub-catchments in the Donnelly Catchment: Donnelly River, Barlee Brook and Carey Brook.  By analysing long-term trends in streamflow, they identified periods when the streams had undergone a hydrological change including changes in flow patterns.

Within these periods Rose-Anne and her collaborators discovered that declining rainfall had caused two of the streams to lose year-round-flow (with statistical changepoints in 1975 and 2001), while the third stream (Carey Brook) had continued to flow all year round. This non-uniform response was attributed to depleted catchment water stores in the streams that had lost year-round flow (Donnelly River and Barlee Brook). This suggests that underlying geology and soil profiles with greater water storage capacity may be enabling the still-flowing stream to buffer changes in rainfall.

Map showing the Donnelly River, Barlee Brook and Carey Brook in the Donnelly catchment. Rainfall gauges and streamflow gauges are also shown, underlain by local geology.

Combining chemistry and hydrology to understand the effects of climate change.

The team also conducted a series of field campaigns to install streamflow loggers and collect surface and groundwater samples to assess streamflow. The samples were then analysed for ion chemistry, radon, stable water isotopes, and radiocarbon in surface water and groundwater, with some of this analysis taking place at ANSTO’s Centre for Accelerator Science (CAS) facility.

Based on this analysis, Rose-Anne was able to demonstrate how and where groundwater was contributing to streamflow.  For example, radon concentrations and radiocarbon trends along the Carey Brook showed the potential for higher levels of groundwater to inflow across the transition zone between hard rock and coastal geological plains.

These results pose an interesting question for future research: what potential impact could hydrogeological features in the landscape, such as the presence of a fault or impermeable geological layer, play in streamflow generation processes and a stream’s ability to buffer climatic stressors?

Investigations such as these are important for understanding surface and groundwater interactions, which will play a crucial role in protecting biodiversity and better preparing these important and diverse ecosystems to resist the worsening effects of climate change.

Rose-Anne Bell using a streamflow gauge at a logger site in Barlee Brook, August 2022.

AINSE are proud to spotlight Rose-Anne Bell for her insightful research.

Read more research spotlights at ainse.edu.au/research-spotlight and keep connected for next month’s Spotlight Series as we dial up the fun for Fungi February!
First up is Carl McCombe, whose research aims to understand how pathogenic fungi attack our important plant crops and how they can be stopped.

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