ORCID Profile
0000-0001-5862-9803
Current Organisations
Flinders University
,
University of Western Australia
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Hydrogeology | Geochemistry | Physical Geography and Environmental Geoscience | Isotope Geochemistry | Surface Processes | Environmental Monitoring | Inorganic Geochemistry | Ecology not elsewhere classified |
Water Allocation and Quantification | Effects of Climate Change and Variability on Australia (excl. Social Impacts) | Mining Land and Water Management | Land and Water Management of environments not elsewhere classified | Ecosystem Adaptation to Climate Change | Urban and Industrial Water Management | Environmental and Natural Resource Evaluation not elsewhere classified | Ecosystem Assessment and Management of Marine Environments
Publisher: Elsevier BV
Date: 12-2016
Publisher: Wiley
Date: 02-04-2014
DOI: 10.1111/GWAT.12052
Abstract: The interpretation of apparent ages often assumes that a water s le is composed of a single age. In heterogeneous aquifers, apparent ages estimated with environmental tracer methods do not reflect mean water ages because of the mixing of waters from many flow paths with different ages. This is due to nonlinear variations in atmospheric concentrations of the tracer with time resulting in biases of mixed concentrations used to determine apparent ages. The bias of these methods is rarely reported and has not been systematically evaluated in heterogeneous settings. We simulate residence time distributions (RTDs) and environmental tracers CFCs, SF6 , (85) Kr, and (39) Ar in synthetic heterogeneous confined aquifers and compare apparent ages to mean ages. Heterogeneity was simulated as both K-field variance (σ(2) ) and structure. We demonstrate that an increase in heterogeneity (increase in σ(2) or structure) results in an increase in the width of the RTD. In low heterogeneity cases, widths were generally on the order of 10 years and biases generally less than 10%. In high heterogeneity cases, widths can reach 100 s of years and biases can reach up to 100%. In cases where the temporal variations of atmospheric concentration of in idual tracers vary, different patterns of bias are observed for the same mean age. We show that CFC-12 and CFC-113 ages may be used to correct for the mean age if analytical errors are small.
Publisher: American Chemical Society (ACS)
Date: 29-08-2023
Publisher: Wiley
Date: 23-07-2021
DOI: 10.1111/GWAT.13120
Abstract: Accurate representation of groundwater flow and solute transport requires a sound representation of the underlying geometry of aquifers. Faults can have a significant influence on the structure and connectivity of aquifers, which may allow permeable units to connect, and aquifers to seal when juxtaposed against lower permeability units. Robust representation of groundwater flow around faults remains challenging despite the significance of faults for flow and transport. We present a methodology for the inclusion of faults utilizing the unstructured grid features of MODFLOW‐USG and MODFLOW 6. The method focuses on the representation of fault geometries using non‐neighbor connections between juxtaposed layers. We present an illustration of the method for a synthetic fluvial aquifer. The combined impact of the heterogeneous aquifer and fault offset is clearly visible where channel features at different depths in the aquifer were connected at the fault. These results highlight the importance of representing fault features in groundwater flow models.
Publisher: Elsevier BV
Date: 10-2022
DOI: 10.1016/J.WATRES.2022.119056
Abstract: The hyporheic zone (HZ) is considered a hydrodynamically-driven bioreactor with significant pollutant removal capacities and can therefore not only improve wholestream water quality but also preserve human and ecosystem health. Microbial metabolism is hypothesized to play a key role in pollutant transformation in hyporheic sediments of natural streams. However, previous work investigating the influence of microbial metabolism on pollutant transformation has been predominantly laboratory studies. The key challenge for field studies is the appropriate determination of net microbial metabolism, i.e. information on the actual exposure times to specific microbial processes in the investigated system. The present study uses reactive fluorescent tracers to determine microbial metabolism and ultimately its influence on pollutant transformation, e.g. for trace organic compounds, in hyporheic sediments under natural conditions. In particular, the reactive fluorescent tracers resazurin and its main transformation product resorufin were used to determine the microbial metabolism of facultative or obligate aerobes. The influence of the derived microbial metabolism on the transformation of 20 trace organic compounds, such as pharmaceuticals, including 3 parent-daughter pairs, was examined. The present findings validate laboratory results on the microbially-mediated transformation of the anticonvulsant gabapentin to its main transformation product gabapentin lactam under natural conditions. All other TrOCs investigated did not show a clear link between TrOC reactivity to the microbial metabolism informed by the resazurin-resorufin-system. Overall, the present study not only demonstrates the use of the fluorescent tracer-system resazurin and resorufin for determining microbial metabolism of facultative or obligate aerobes but also generally highlights the potential of reactive fluorescent tracers to disentangle specific reactive properties and ultimately their influence on the fate of pollutants in natural HZs.
Publisher: Elsevier BV
Date: 11-2021
Publisher: Wiley
Date: 13-06-2019
DOI: 10.1111/GWAT.12797
Abstract: Hydraulic head differences across the screened or open interval of a well significantly influence the s led water mixture. S le bias can occur due to an insufficient pumping rate and/or due to native groundwater displacement by intraborehole flow (IBF). Proper understanding of the s led water mixture is crucial for accurate interpretation of environmental tracers and groundwater chemistry data, and hence groundwater characterization. This paper uses numerical modeling to quantify s le bias caused by IBF in an un-pumped high-yield well, and the influence of pumping rate and heterogeneity on the volume of pumpage required to purge an IBF plume. The results show that (1) the pumping rate must be at least an order of magnitude greater than the IBF rate to achieve permeability-weighted yield, (2) purge volume was 2.2 to 20.6 times larger than the IBF plume volume, with the ratio depending on plume location relative to hydraulic conductivity and head distributions, and (3) after an ex le 1000-day un-pumped period, purging required removal of at least three orders of magnitude more water than the common practice of three to five well volumes. These results highlight the importance of knowing the borehole flow regime to identify IBF inflow and outflow zones, estimate IBF rates, and to develop a strategic s ling approach.
Publisher: Wiley
Date: 12-07-2015
DOI: 10.1111/GWAT.12237
Abstract: Apparent ages obtained from the measured concentrations of environmental tracers have the potential to inform recharge rates, flow rates, and assist in the calibration of groundwater models. A number of studies have investigated sources of error in the relationships between the apparent ages, and the age assumed by models to relate this quantity to an aquifer property (e.g., recharge). These studies have also provided a number of techniques for correcting the known biases of apparent ages. In this paper, we review some of the concepts of age bias. We then demonstrate this bias through the use on four numerical ex les, and assess the accuracy of correction methods in overcoming this bias. We examine this for CFCs, SF6, 3H/3He, 39Ar, and 14C. We demonstrate that in our four simple steady-state aquifer ex les, bias occurs for a wide range of environmental tracers and flow configurations. When applying correction methods, we found that the values obtained are limited by the model assumptions. Models accounting for exchange with aquitards represent whole mobile zones and not discrete well screens. Mean transit times (comparable to mean ages) obtained from lumped parameter models deviate from actual values as the assumed distribution varies from the actual distribution. Methods that use multiple tracer ages are limited to ranges where both tracers report apparent ages. Our findings suggest that the incorporation of environmental tracer data into the understanding of groundwater systems requires approaches such as the direct use of concentrations, or the simulation of full age distributions.
Publisher: Elsevier BV
Date: 02-2020
Publisher: American Geophysical Union (AGU)
Date: 07-2019
DOI: 10.1029/2018WR024103
Publisher: Elsevier BV
Date: 2012
Publisher: Elsevier BV
Date: 07-2021
Publisher: Springer Science and Business Media LLC
Date: 08-09-2012
Publisher: Elsevier BV
Date: 07-2019
Publisher: Springer Science and Business Media LLC
Date: 19-11-2012
Publisher: Wiley
Date: 25-04-2012
DOI: 10.1111/J.1745-6584.2011.00821.X
Abstract: Recognizing the underlying mechanisms of bank storage and return flow is important for understanding streamflow hydrographs. Analytical models have been widely used to estimate the impacts of bank storage, but are often based on assumptions of conditions that are rarely found in the field, such as vertical river banks and saturated flow. Numerical simulations of bank storage and return flow in river-aquifer cross sections with vertical and sloping banks were undertaken using a fully-coupled, surface-subsurface flow model. Sloping river banks were found to increase the bank infiltration rates by 98% and storage volume by 40% for a bank slope of 3.4° from horizontal, and for a slope of 8.5°, delay bank return flow by more than four times compared with vertical river banks and saturated flow. The results suggested that conventional analytical approximations cannot adequately be used to quantify bank storage when bank slope is less than 60° from horizontal. Additionally, in the unconfined aquifers modeled, the analytical solutions did not accurately model bank storage and return flow even in rivers with vertical banks due to a violation of the dupuit assumption. Bank storage and return flow were also modeled for more realistic cross sections and river hydrograph from the Fitzroy River, Western Australia, to indicate the importance of accurately modeling sloping river banks at a field scale. Following a single wet season flood event of 12 m, results showed that it may take over 3.5 years for 50% of the bank storage volume to return to the river.
Publisher: Springer Science and Business Media LLC
Date: 06-07-2010
Publisher: Springer Science and Business Media LLC
Date: 06-07-2010
Publisher: Springer Science and Business Media LLC
Date: 04-04-2017
Publisher: Elsevier BV
Date: 11-2020
Publisher: Wiley
Date: 20-11-2023
DOI: 10.1111/GWAT.13273
Abstract: Sedimentary structures have unique geometries and anisotropic hydraulic conductivity, both of which control groundwater flow. Traditional finite‐difference simulators (e.g., MODFLOW) have not been able to correctly represent irregular, dipping and anisotropic structures due their use of a simplified conductivity tensor, causing many modelers to turn toward finite‐element codes with their sophisticated meshing capabilities. However, the release of MODFLOW 6 with its flexible discretization and multipoint flux approximation scheme prompts us to revisit its capability to compute flow through complex sedimentary structures. Through the use of a novel benchmark and case study, we show that when versions previous to MODFLOW 6 are applied to dipping structures, modeled fluxes and hence flow through the system, can be significantly over or underestimated. For ex le, effective conductivity for a 30° dipping layer with a 100:1 conductivity ratio is reduced to only 2% of its inputted value. We show that MODFLOW 6, with its XT3D capability and flexible discretization options is far superior to its predecessors, allowing flow through complex sedimentary structures to be simulated more accurately. However, on vertically offset grids, which have been available in all versions of MODFLOW and are often used in practice, loss of accuracy is still a concern when the vertical offset is large, that is, the dip of the sedimentary layer is steep, particularly if the layer is much more conductive than the surrounding material. The hypothesis that vertically offset grids lack sufficient hydraulic connectivity between adjacent model layers to accurately simulate the steeply dipping, highly heterogeneous case is a topic for further investigation.
Publisher: American Chemical Society (ACS)
Date: 07-10-2018
Abstract: First-order half-lives for 26 trace organic compounds (TrOCs) were determined in the hyporheic zone (HZ) and along a 3 km reach of a first-order stream in South Australia during both dry and wet seasons. Two salt tracer experiments were conducted and evaluated using a transient storage model to characterize seasonal differences in stream residence time and transient storage. Lagrangian and time-integrated surface water s ling were conducted to calculate half-lives in the surface water. Half-lives in the HZ were calculated using porewater s les obtained from a modified mini-point s ler and hyporheic residence times measured via active heat-pulse sensing. Half of the investigated TrOCs (e.g., oxazepam, olmesartan, candesartan) were not significantly removed along both the investigated river stretch and the s led hyporheic flow paths. The remaining TrOCs (e.g., metformin, guanylurea, valsartan) were found to be significantly removed in the HZ and along the river stretch with relative removals in the HZ correlating to reach-scale relative removals. Using the modeled transport parameters, it was estimated that wet season reach-scale removal of TrOCs was predominately caused by removal in the HZ when the intensity of hyporheic exchange was also higher. Factors that increase HZ exchange are thus likely to promote in-stream reactivity of TrOCs.
Publisher: Elsevier BV
Date: 11-2018
Publisher: Elsevier BV
Date: 12-2023
Publisher: American Geophysical Union (AGU)
Date: 2015
DOI: 10.1002/2014WR015779
Publisher: Springer Science and Business Media LLC
Date: 24-01-2014
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.SCITOTENV.2015.08.036
Abstract: Groundwater within the coastal aquifer systems of the Daweijia area in northeastern China is characterized by a large of variations (33-521mg/L) in NO3(-) concentrations. Elevated nitrate concentrations, in addition to seawater intrusion in the Daweijia well field, both attributable to anthropogenic activities, may impact future water-management practices. Chemical and stable isotopic (δ(18)O, δ(2)H) analysis, (3)H and CFCs methods were applied to provide a better understanding of the relationship between the distribution of groundwater mean residence time (MRT) and nitrate transport, and to identify sources of nitrate concentrations in the complex coastal aquifer systems. There is a relatively narrow range of isotopic composition (ranging from -8.5 to -7.0‰) in most groundwater. Generally higher tritium contents observed in the wet season relative to the dry season may result from rapid groundwater circulation in response to the rainfall through the preferential flow paths. In the well field, the relatively increased nitrate concentrations of groundwater, accompanied by the higher tritium contents in the wet season, indicate the nitrate pollution can be attributed to domestic wastes. The binary exponential and piston-flow mixing model (BEP) yielded feasible age distributions based on the conceptual model. The good inverse relationship between groundwater MRTs (92-467years) and the NO3(-) concentrations in the shallow Quaternary aquifers indicates that elevated nitrate concentrations are attributable to more recent recharge for shallow groundwater. However, there is no significant relationship between the MRTs (8-411years) and the NO3(-) concentrations existing in the carbonate aquifer system, due to the complex hydrogeological conditions, groundwater age distributions and the range of contaminant source areas. Nitrate in the groundwater system without denitrification effects could accumulate and be transported for tens of years, through the complex carbonate aquifer matrix and the successive inputs of nitrogen from various sources.
Publisher: American Geophysical Union (AGU)
Date: 11-2018
DOI: 10.1029/2018WR022800
Publisher: Elsevier BV
Date: 06-2023
Publisher: American Geophysical Union (AGU)
Date: 03-2020
DOI: 10.1029/2019WR024987
Publisher: Elsevier BV
Date: 03-2016
Publisher: Elsevier BV
Date: 08-2023
Publisher: American Geophysical Union (AGU)
Date: 07-2010
DOI: 10.1029/2009WR008539
Publisher: American Geophysical Union (AGU)
Date: 02-2017
DOI: 10.1002/2016WR019839
Abstract: Understanding groundwater ages offers insight into the time scales of recharge, aquifer storage turnover times, and contaminant protection time frames. The ability to quantify groundwater age distributions heavily depends on the choice of the interpretive model, and often important features of the age distribution cannot be identified with the subset of available models. In this paper, we implemented a multiple tracer method using a technique that assumes limited details regarding the shape of the age distribution and applied it to dewatering wells at a mine site in the Pilbara region of north‐western Australia. Using our method, we were able to identify distinct age components in the groundwater. We calculated the presence of four distinct age groups in the s les. All wells contained water aged between zero and 20 years. However, the rest of the s les were composed of water between 50 and 100 years, 100 and 600 years, or water approximately 1000 years old. These were consistent with local recharge sources (50–100 years) and knowledge of paleoclimate from lake sediment records. We found that although the age components were well constrained, the relative proportions of each component were highly sensitive to errors of environmental tracer data. Our results show that our method can identify distinct age groups in groundwater s les without prior knowledge of the age distribution. The presence of distinct recharge times gives insight into groundwater flow conditions over long periods of time.
Publisher: American Geophysical Union (AGU)
Date: 11-2012
DOI: 10.1029/2012WR012103
Publisher: American Geophysical Union (AGU)
Date: 31-07-2020
DOI: 10.1029/2020WR027240
Abstract: Determining variations in groundwater replenishment over a variety of time scales remains a challenge in the management and protection of groundwater resources. Specifically, capacity to use hydraulic data collected in small windows of time to infer long‐term changes can be limited by system responses. Groundwater ages offer an alternative approach as they represent the time since recharge occurred. Here we use spatial variations in groundwater ages and environmental tracer concentrations to infer temporal variations in groundwater recharge and apply the method to a mine site in northwest Australia, where a stream has been modified from ephemeral to perennial, resulting in enhanced recharge to groundwater. Measurements of 14 C and CFC‐12 at five transects along an ephemeral stream were interpreted with the new model to identify recharge rates and the proportion of recharge attributable to enhanced versus natural recharge from flood events. Enhanced recharge varied between 0.03 and 0.66 m/year compared to flood‐generated recharge values ranging between 0.07 and 1.3 m/year. Our results show that spatial variations of groundwater ages and environmental tracer concentrations preserve information about past flow regimes. While our study has demonstrated decadal variations in recharge, application of the method on larger scales could infer much greater extent of temporal variability in recharge, with the potential for significant insight into climate effects on groundwater.
Publisher: Elsevier BV
Date: 12-2016
Publisher: American Geophysical Union (AGU)
Date: 03-2016
DOI: 10.1002/2015WR017441
Abstract: The biogeochemical functioning of stream ecosystems is heavily dependent on water and water‐borne nutrient fluxes between the stream itself and the streambed and banks (i.e., the hyporheic zone). The travel time of water exchanges through the hyporheic zone has been investigated previously however, these studies have primarily modeled exchanges under steady state conditions assuming spatial pressure variations. This assumes that the hydraulic gradients that drive the exchanges are maintained the whole time the stream water remains in the bed or banks, which is unrealistic. Therefore, in this study we use a transient approach to investigate residence time distributions (RTDs) of bank inflow and bank outflow during both regular, diurnal stream stage variations and storm flow events. We demonstrate that RTDs reflect the timing and magnitude bank inflows, rather than smooth RTDs. We also show that small percentages of water from a given bank inflow event may be present in bank outflows for long periods of time, due to dispersion and diffusion within the bank, and lower rates of bank outflow, relative to bank inflow. This is apparent in the synthetic model of a single storm flow event, where 10% remained in the bank after 50 days. Additionally, residence times for a given bank inflow event are longer when repeated events occur, because the bank outflows from one event are “interrupted” by an increase in stream stage during a successive event. For ex le, field data capturing events of variable timing and magnitude showed that 70 days after each of three storm flow events occurred, 40, 12 and 30% of the bank inflow event remained in the banks. These cases indicate that bank exchanges are temporally dynamic and the RTDs of return flows can have significant tailing, which will dictate rates of nutrient exchange within the near‐stream environment.
Publisher: American Geophysical Union (AGU)
Date: 03-2014
DOI: 10.1002/2013WR014974
Publisher: American Geophysical Union (AGU)
Date: 12-2022
DOI: 10.1029/2021GL096570
Abstract: Analyzing groundwater systems in transient state is essential for understanding the response of groundwater recharge to changing environments. Radioactive isotopes have long been used to track recharge behavior, typically under steady state conditions. This study tests the limitations of using radioactive isotopes in confined aquifers and under transient conditions to sense changes in groundwater recharge rates over time. Four system parameters determine the bounds of this approach: the isotope half‐life, the Péclet number (Pe), and mobile‐immobile zone interactions. This study revealed that in confined groundwater systems where Pe ≥ 10, isotopes reflect transience when the half‐life matches the water travel time down the flow path or the time elapsed from the change in velocity. This response is evident regardless of mobile‐immobile interaction, suggesting that appropriate isotope selection is key to establishing past recharge regardless of aquifer lithology or geometry.
Publisher: Copernicus GmbH
Date: 20-03-2018
DOI: 10.5194/HESS-22-1917-2018
Abstract: Abstract. Profiles of temperature time series are commonly used to determine hyporheic flow patterns and hydraulic dynamics in the streambed sediments. Although hyporheic flows are 3-D, past research has focused on determining the magnitude of the vertical flow component and how this varies spatially. This study used a portable 56-sensor, 3-D temperature array with three heat pulse sources to measure the flow direction and magnitude up to 200 mm below the water–sediment interface. Short, 1 min heat pulses were injected at one of the three heat sources and the temperature response was monitored over a period of 30 min. Breakthrough curves from each of the sensors were analysed using a heat transport equation. Parameter estimation and uncertainty analysis was undertaken using the differential evolution adaptive metropolis (DREAM) algorithm, an adaption of the Markov chain Monte Carlo method, to estimate the flux and its orientation. Measurements were conducted in the field and in a sand tank under an extensive range of controlled hydraulic conditions to validate the method. The use of short-duration heat pulses provided a rapid, accurate assessment technique for determining dynamic and multi-directional flow patterns in the hyporheic zone and is a basis for improved understanding of biogeochemical processes at the water–streambed interface.
Start Date: 11-2022
End Date: 11-2026
Amount: $770,288.00
Funder: Australian Research Council
View Funded ActivityStart Date: 04-2018
End Date: 09-2024
Amount: $364,200.00
Funder: Australian Research Council
View Funded ActivityStart Date: 02-2020
End Date: 02-2024
Amount: $838,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 09-2021
End Date: 12-2024
Amount: $704,711.00
Funder: Australian Research Council
View Funded Activity