Author: Steve Flook
Flook, Steve, 2024 Enhancing the understanding of groundwater–surface water interaction in the northern Surat Basin, Flinders University, College of Science and Engineering
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Understanding sub-regional relationships between groundwater and surface water resources – magnitude, timing and direction of flux – is an important element to inform effective water resource management, particularly in highly connected systems. The Dawson River and Hutton Creek are regionally significant watercourses within the southern Fitzroy River catchment. In this area, there is significant resource development and groundwater use, with the potential to alter the groundwater–surface water connectivity regime.
This thesis focuses on enhancing the understanding of groundwater–surface water interaction along two stream sections interpreted to be receiving discharge from the Precipice Sandstone, the basal aquifer of the Great Artesian Basin (GAB). The presence of permanent water within these semi-arid landscapes are intrinsically linked to significant cultural values and ecological diversity. Understanding this interact is necessary to assess changes in the existing flow regimes which may result from groundwater development or climate change.
Beyond dissection and erosion of the overlying and confining unit by surface water, it is hypothesised that other geomorphic characteristics – faults and fractures, variability in stream substrate and stream slope – may influence the location of groundwater discharge to stream. To evaluate this hypothesis, this thesis integrates stream gauging and environmental tracer data to assess the spatial variability, direction and magnitude of flux, and the local and regional groundwater flow components of stream discharge.
The study locations occur within the deeply dissected sandstone tablelands dominated by shallow and rocky soils. The bedrock geology – the lower Jurassic Surat Basin sequence – was deposited upon the eroded and folded Bowen Basin, with two regional structural features proximal to the study locations – the Hutton-Wallumbilla fault system and the Arcadia Anticline.
Stream gauging and environmental tracer data – Radiocarbon (14C), Tritium (3H), Radon (222Rn), Oxygen (18O), Deuterium (2H) and Strontium (Sr) – were concurrently collected during optimal baseflow conditions and historical bore sampling data were compiled for the analysis.
Analysis of stream gauging data indicates total groundwater discharge from these reaches is approximately 6,500 ML/yr – 90% of which is associated with the Dawson River. Differential stream gauging analysis highlights the presence of significant inter-reach variability, in terms of both the direction and magnitude of flux to the surrounding groundwater system.
Environmental isotope data provided complementary and additional insights to the stream gauging data – 222Rn data supported the refinement of zones of higher groundwater flux and 14C, 3H, 18O and 2H identified reaches dominated by either local or regional groundwater flow. Hutton Creek has one zone dominated by regional groundwater flow. The Dawson River is also dominated by regional groundwater discharge, downstream of the confluence of Hutton Creek. Significant variability in groundwater discharge is observed however, which appears controlled by factors beyond the geology, stream slope or substrate.
Consistent with recent studies in the northern Surat Basin, the stream gauging and environmental tracer data indicate a high degree of local variability, with higher discharge zones likely to be the result of secondary porosity within the Precipice Sandstone, potentially related to the interaction between the Surat Basin and underlying regional structures in the Bowen Basin.
This thesis highlights the benefits of integrating stream gauging and environmental tracer data to enhance the understanding of the internal dynamics of the broader discharge zone. The environmental tracer data were analysed and elucidated deeper insights into the zones and sources of groundwater discharge, which are unable to be determined from stream gauging alone. This is a critically important consideration in assessing the implications of future climate regimes, impacts from groundwater extraction, and consequences on dependent ecosystems and values.
Keywords: baseflow, environmental tracers, stream flow, groundwater-surface water interaction, groundwater-dependent ecosystems
Subject: Hydrology thesis
Thesis type: Masters
Completed: 2024
School: College of Science and Engineering
Supervisor: Okke Batelaan