Integrated Use of Geological, Geophysical, Radiocarbon and Stable Isotopes Data for Tracing the Conduit Flow Paths in a Small Karstic Aquifer: Poocher Swamp Freshwater Lens, South Australia

Abstract

An integrated approach combining lithological logs, downhole geophysics, electromagnetic survey and the distribution of radiocarbon ( 14 C) and the stable isotopes of water molecules ( 18 O) were used to identify the conduit flow paths of a small freshwater lens. Lost circulation zones, where drilling fluid flows into geological formation instead returning up the annulus recorded during water well drilling, were considered as the major fracture zones. The presence of high porosity zones within boreholes were identified using caliper, gamma and neutron logs. These methods were used to identify the depth intervals at which cavities and the existence of conduit porosity within the boreholes. Transient electromagnetic (TEM) method was used to investigate resistivity anomalies in the profiles along nine pre-determined lines across the freshwater lens. Resistivity anomalies were related to borehole information and other surface features such as sinkholes. Low resistivity zones of the TEM tomography sections had excellent correlation to fracture zones identified during well drilling, and downhole geophysical logs. Similarly, high resistivity zones in the profiles correlate well with the zones of O signatures of the groundwater confirm the presence of conduits and potential pathways of preferential flows. This investigation illustrates the effectiveness using an integrated approach to trace the conduit flow paths in karst aquifers. The information gained from the study is currently being used for the management of the freshwater lens.

Water Supply Source Evaluation in Unmanaged Aquifer Recharge Zones: The Mezquital Valley (Mexico) Case Study

“…However, integrated approaches (e.g., [32]) such as the one we present are comparatively scarce in the groundwater literature. More specifically, these have seldom been used for the purpose of characterizing groundwater bodies, and their application in the context of unmanaged aquifer recharge is practically non-existent.…”

Karst Conduit Networks, Connectivity and Recharge Dynamics of a Sinkhole

“…Synchronisation was controlled directly using the GDP-32ii receiver. Data were then used to produce 1D inversion model sections of resistivity using Zonge International's STEMINV modelling program (Somaratne & Mann, 2016). The survey was conducted on 5-13 January 2017, allowing two months of draining of the soil profile following the rain or irrigation.…”

“…The freshwater lens is surrounded by brackish water. The catchment area extends across the South Australian border into western Victoria and previously described by Somaratne (2014) and Somaratne and Mann (2016). For brevity, a succinct summary of the study freshwater lens is provided here.…”

“…This is because lithological samples are typically collected at certain depth intervals (in this case 3 m) and hence represent an average of the samples collected within the depth interval. Therefore, combining geophysical logs with lithological logs is more useful for interpretation than relying on only one set of logs (Somaratne & Mann, 2016). Because of lost circulation below 22.5 m depth, two wells critical to this study; WRG034 and WRG035 ( Figure 4 are the response of neutron counters which are highly sensitive to the amount of hydrogen around the sonde and thus the porosity.…”

“…Dryland grazing is common within the lens area and the surroundings. As such, prudent management of the Poocher Swamp fresh water lens is vital for sustaining local economic activities (Somaratne & Mann, 2016).…”