Combining geophysics, near surface chemistry and environmental … · 2017-07-31 · TEMPEST AEM...
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FOR FURTHER INFORMATION Figure 2: Interpretation of palaeohydrology derived from airborne magnetics 1 st Vertical Derivative, draped over SRTM 1sec DEM REFERENCES FrOG Tech. 2005. OZ SEEBASE TM v1 Structural GIS http://www.frogtech.com.au/seebase-range Harrington, G.A., and Harrington, N.M., (2017) Hydrochemistry of peat mound springs within Mandora Marsh, West Canning Basin, W.A., A report prepared for Department of Parks and Wildlife Western Australia by Innovative Groundwater Solutions. Leech, R.E.J., 1979. Geology and groundwater resources of the Southwestern Canning Basin, Western Australia. Geological Survey of Western Australia. Record 1979/9. Perth 1979. ISBN No. 072448034X. V&C Semeniuk Research Group (2000) Wetlands of the northwestern Great Sandy Desert; in the LaGrange hydrological sub-basin. A report prepared for Water and Rivers Commission Western Australia. Van der Graff, W.J.E., Crowe, W.R.A., Bunting, J.A., and Jackson, M.J., (1977) Relict early Cenozoic drainages in arid Western Australia. Zeitschrift fur Geomorphologie 21:4 379-400. ACKNOWLEDGEMENTS We respectively acknowledge the Nyangumarta as the traditional owners of the land on which the spring survey was conducted. We are grateful to you for imparting your cultural knowledge, for introducing us to the springs and wetlands of Walyarta and for assistance in the 2015 and 2016 field surveys. DBCA Principal Ecologist Val English for requesting the investigation and staff of the Kimberley Region for coordinating the field programs, in particular Tracy Sonneman and Naomi Findlay. BHP Billiton for funding this work. Department of Agriculture and Food (DAFWA) and Department of Water (DoW) for sharing data collected across the Canning Basin. Combining geophysics, near surface chemistry and environmental tracers to define a critical ecohydrological management zone for the Walyarta (Mandora Marsh) mound springs, Australia Hydrogeology Advective flow along geological faults (Wallal aquifer) and throughflow-discharge (Broome aquifer) are thought to be the main groundwater processes that sustain mound spring discharge in Mandora Marsh. These Canning Basin Mesozoic aquifers have similar lithology's (sandstone with rare siltstone interbeds), groundwater type (Na-Cl to Na-Ca-Cl-HCO 3 and are separated by a generally thick, laterally continuous siltstone-claystone aquitard of Jurassic age (Jarlemai Siltstone) (Leech 1979). Average annual rainfall is low (~370mm) and potential evaporation high (>3,000mm p.a.). Groundwater recharge to the Wallal aquifer is variable, via throughflow and vertically through the Broome Sandstone and Jarlemai Siltstone. As a result groundwater in the Wallal aquifer is older and has a different environmental isotope signature (e.g. lower pMC 14 C activities (~10 pMC) and depleted in δ 2 H) (Harrington & Harrington 2014). Mound Spring Discharge – Aquifer Fingerprinting The Mandora Marsh is remote and the mound springs difficult to access (Fig 1a&b). Two four day field programs were undertaken yielding a total of 23 samples (Sept 2015 (fifteen samples) and Nov 2016 (eight samples)). Water was sampled in the field for pH, EC, temperature and samples collected and analysed for major ions, nutrients, metals, rare earth elements and environmental isotopes δ 2 H, δ 18 O, 87 Sr/ 86 Sr, 14 C, 13 C/ 12 C. As few groundwater bores are located in the study area spring hydrochemistry data were interpreted with historical groundwater datasets collected north and south of the study area. Results showed that approx. 25% of the spring discharge samples from ‘1. mid slope flowing’ sites (see Fig 1b) had a δ 2 H, δ 18 O and 14 C composition indicating significant groundwater discharge from the Wallal aquifer, indicating advective flow along geological faults is important for the spring water balance. The Ramsar listed Mandora Marsh mound spring and wetland system is located in the west Canning Basin, in the arid zone of the Great Sandy Desert, north-west Western Australia. The artesian mound spring system has high ecological values, hosting unique phreatophytic vegetation communities and perennial and ephemeral water bodies inhabited by fish and invertebrates. Little is known of the current hydrological function of the mound springs. With an increased water demand and climate change there is an urgent need to gain this knowledge and develop a robust approach to their management. Jasmine Rutherford 1 , Glenn Harrington 2 ,Neil Milligan 3 , Camilla Soerenson 4 , Steven Batty 5 , Lindsay Bourke 1 and Tim Munday 4 1 Department of Biodiversity, Conservation and Attractions 2 Innovative Groundwater Solutions 3 Cymod Systems Pty Ltd 4 CSIRO Mineral Resources 5 Target Geoscience DEPARTMENT OF BIODIVERSITY, CONSERVATION AND ATTRACTIONS (SCIENCE AND CONSERVATION) Jasmine Rutherford e [email protected] w www.dpaw.wa.gov.au Figure 3: Pseudocoloured TEMPEST AEM interval conductivities (a. 0-10m, b. 60-70m) over magnetics 1VD, showing structural interpretation and location of flight line L40026. Management Strategies Encourage the development of a groundwater management strategy and monitoring plan that appreciates the risks associated of depressurising the Wallal aquifer through groundwater abstraction (e.g. anisotropic drawdown along geological faults and potential compartmentalised pumping responses (e.g. horst-graben and palaeochannels). Continue to research and assess technologies and methods to resolve and understand hydrogeological / ecohydrological controls on surface water and groundwater movement and define effective management zone boundaries. Figure 1: a. Mandora Marsh Project Area (showing bores sampled within area) b. Mound spring and groundwater environmental isotope data (plotted δ 18 O vs δ 2 H); schematic showing variation in 14 C in relation to the location sampled across a typical mound spring and photographs from the Nov 2016 program showing site transport and sampling methods. Figure 5: Modflow/MT3D 14 C concentrations at the watertable, following a 15000 year transient solute transport simulation (Fig 1a shows the location of modelling results) Hydrology and Geomorphology An integrated interpretation of airborne magnetic data (1 st vertical derivative) with the SRTM 1sec DEM shows mound springs are located within and up- gradient of the valley floor (Fig 2). Under the current climate, waterbodies are ephemeral and the valley floor contains thin valley fill sediments that include evaporates (halite and carbonates). Low-frequency, dominant NW-SE magnetic responses resolve deeper palaeodrainage channels located west and south of the mound springs. In the valley floor, shallow high-frequency magnetic responses correspond with later beach/slope and strandlines and are likely to be related to the last major sea level high stand in the Pleistocene (Semeniuk 2000). Both the deep and shallow palaeodrainage networks evident in the magnetic data follow major geological structural trends, which is common (Van der Graff 1977). Numerical modelling A simplified geological structural model was constructed using Leapfrog Geo 3D™ for the development of a fault block numerical model. An existing numerical saturated flow model, as developed by the Department of Water WA, was modified using Modflow/MT3D to simulate the behaviour of flow along geological faults and the exponential decay of 14 C using a 3D solute transport model. Rainfall and the Wallal aquifer were assigned 14 C concentrations of 100 and 10 pMC respectively. The model was run as steady state flow and transient solute transport for 15000 years, with the resulting distribution of 14 C at the water table accounting for decay as well as horizontal and vertical flow (Fig 5). Modelling results provide a proof of concept that fault conduits and elevated hydraulic heads in the Wallal aquifer can facilitate discrete discharge of older, deeper groundwater. Modelling of conservative tracers is currently being undertaken to verify these results. a. b. Figure 4: TEMPEST AEM conductivity-depth section for flight line L40026 (Fig 3), showing the depth of investigation (DoI) for the TEMPEST system, the location of interpreted transfer and normal faults (dashed lines), and groundwater conductivity (mS/m), for northern-most spring on L40026 (Stockyard Mangrove Spring). a. b. Structure and Airborne Geophysics The main structural styles from an integrated interpretation of airborne magnetics and electromagnetics resolve NW-SE transfer faults separating horst and grabens, with WSW-ENE normal faulting showing relay displacement at the Mandora Marsh valley margin, close to mound springs (Fig 3 a&b). Mapped and sampled mound springs occur in potential zones of dilation in a transpressional setting (at the intersection of transfer and normal faults) to a depth of at least 200 meters below ground level (Fig 4). FrOG TECH (2005) describe similar structural styles for the Canning Basin and advised reactivation of these faults was likely in the Miocene to Recent (21-5 Ma), making the faults visible in contemporary landscape and influencing the location of Quaternary and current drainage lines. Stockyard Mangrove Spring Spring groundwater discharge: 345 mS/m Broome aquifer Jarlemai Siltstone Stockyard Mangrove Spring DoI POSTER PRESENTED The 3 rd American Geophysical Union-Society of Exploration Geophysicists Hydrogeophysics Workshop: Imaging the Critical Zone, Stanford California 24-27 July 2017 (http://workshops.agu.org/hydrogeophysics/)
Transcript of Combining geophysics, near surface chemistry and environmental … · 2017-07-31 · TEMPEST AEM...
FOR FURTHER INFORMATION
Figure 2: Interpretation of palaeohydrology derived from airborne magnetics 1st Vertical Derivative, draped over SRTM 1sec DEM
REFERENCES FrOG Tech. 2005. OZ SEEBASETM v1 Structural GIS http://www.frogtech.com.au/seebase-range Harrington, G.A., and Harrington, N.M., (2017) Hydrochemistry of peat mound springs within Mandora Marsh, West Canning Basin, W.A., A report prepared for Department of Parks and Wildlife Western Australia by Innovative Groundwater Solutions. Leech, R.E.J., 1979. Geology and groundwater resources of the Southwestern Canning Basin, Western Australia. Geological Survey of Western Australia. Record 1979/9. Perth 1979. ISBN No. 072448034X. V&C Semeniuk Research Group (2000) Wetlands of the northwestern Great Sandy Desert; in the LaGrange hydrological sub-basin. A report prepared for Water and Rivers Commission Western Australia. Van der Graff, W.J.E., Crowe, W.R.A., Bunting, J.A., and Jackson, M.J., (1977) Relict early Cenozoic drainages in arid Western Australia. Zeitschrift fur Geomorphologie 21:4 379-400.
ACKNOWLEDGEMENTS We respectively acknowledge the Nyangumarta as the traditional owners of the land on which the spring survey was conducted. We are grateful to you for imparting your cultural knowledge, for introducing us to the springs and wetlands of Walyarta and for assistance in the 2015 and 2016 field surveys. DBCA Principal Ecologist Val English for requesting the investigation and staff of the Kimberley Region for coordinating the field programs, in particular Tracy Sonneman and Naomi Findlay. BHP Billiton for funding this work. Department of Agriculture and Food (DAFWA) and Department of Water (DoW) for sharing data collected across the Canning Basin.
Combining geophysics, near surface chemistry and environmental tracers to define a critical ecohydrological management zone for the Walyarta (Mandora Marsh) mound springs, Australia
Hydrogeology Advective flow along geological faults (Wallal aquifer) and throughflow-discharge (Broome aquifer) are thought to be the main groundwater processes that sustain mound spring discharge in Mandora Marsh. These Canning Basin Mesozoic aquifers have similar lithology's (sandstone with rare siltstone interbeds), groundwater type (Na-Cl to Na-Ca-Cl-HCO3 and are separated by a generally thick, laterally continuous siltstone-claystone aquitard of Jurassic age (Jarlemai Siltstone) (Leech 1979).
Average annual rainfall is low (~370mm) and potential evaporation high (>3,000mm p.a.). Groundwater recharge to the Wallal aquifer is variable, via throughflow and vertically through the Broome Sandstone and Jarlemai Siltstone. As a result groundwater in the Wallal aquifer is older and has a different environmental isotope signature (e.g. lower pMC 14C activities (~10 pMC) and depleted in δ2H) (Harrington & Harrington 2014).
Mound Spring Discharge – Aquifer Fingerprinting The Mandora Marsh is remote and the mound springs difficult to access (Fig 1a&b). Two four day field programs were undertaken yielding a total of 23 samples (Sept 2015 (fifteen samples) and Nov 2016 (eight samples)). Water was sampled in the field for pH, EC, temperature and samples collected and analysed for major ions, nutrients, metals, rare earth elements and environmental isotopes δ2H, δ18O, 87Sr/86Sr, 14C, 13C/12C.
As few groundwater bores are located in the study area spring hydrochemistry data were interpreted with historical groundwater datasets collected north and south of the study area. Results showed that approx. 25% of the spring discharge samples from ‘1. mid slope flowing’ sites (see Fig 1b) had a δ2H, δ18O and 14C composition indicating significant groundwater discharge from the Wallal aquifer, indicating advective flow along geological faults is important for the spring water balance.
The Ramsar listed Mandora Marsh mound spring and wetland system is located in the west Canning Basin, in the arid zone of the Great Sandy Desert, north-west Western Australia. The artesian mound spring system has high ecological values, hosting unique phreatophytic vegetation communities and perennial and ephemeral water bodies inhabited by fish and invertebrates. Little is known of the current hydrological function of the mound springs. With an increased water demand and climate change there is an urgent need to gain this knowledge and develop a robust approach to their management.
Jasmine Rutherford1, Glenn Harrington2,Neil Milligan3, Camilla Soerenson4, Steven Batty5, Lindsay Bourke1 and Tim Munday4
1Department of Biodiversity, Conservation and Attractions 2Innovative Groundwater Solutions 3Cymod Systems Pty Ltd 4CSIRO Mineral Resources 5Target Geoscience
DEPARTMENT OF BIODIVERSITY, CONSERVATION AND ATTRACTIONS (SCIENCE AND CONSERVATION)
Jasmine Rutherford e [email protected] w www.dpaw.wa.gov.au
Figure 3: Pseudocoloured TEMPEST AEM interval conductivities (a. 0-10m, b. 60-70m) over magnetics 1VD, showing structural interpretation and location of flight line L40026.
Management Strategies Encourage the development of a groundwater management strategy and monitoring plan that appreciates the risks associated of depressurising the Wallal aquifer through groundwater abstraction (e.g. anisotropic drawdown along geological faults and potential compartmentalised pumping responses (e.g. horst-graben and palaeochannels).
Continue to research and assess technologies and methods to resolve and understand hydrogeological / ecohydrological controls on surface water and groundwater movement and define effective management zone boundaries.
Figure 1: a. Mandora Marsh Project Area (showing bores sampled within area) b. Mound spring and groundwater environmental isotope data (plotted δ18O vs δ2H); schematic showing variation in 14C in relation to the location sampled across a typical mound spring and photographs from the Nov 2016 program showing site transport and sampling methods.
Figure 5: Modflow/MT3D 14C concentrations at the watertable, following a 15000 year transient solute transport simulation (Fig 1a shows the location of modelling results)
Hydrology and Geomorphology An integrated interpretation of airborne magnetic data (1st vertical derivative) with the SRTM 1sec DEM shows mound springs are located within and up- gradient of the valley floor (Fig 2).
Under the current climate, waterbodies are ephemeral and the valley floor contains thin valley fill sediments that include evaporates (halite and carbonates).
Low-frequency, dominant NW-SE magnetic responses resolve deeper palaeodrainage channels located west and south of the mound springs.
In the valley floor, shallow high-frequency magnetic responses correspond with later beach/slope and strandlines and are likely to be related to the last major sea level high stand in the Pleistocene (Semeniuk 2000).
Both the deep and shallow palaeodrainage networks evident in the magnetic data follow major geological structural trends, which is common (Van der Graff 1977).
Numerical modelling A simplified geological structural model was constructed using Leapfrog Geo 3D™ for the development of a fault block numerical model.
An existing numerical saturated flow model, as developed by the Department of Water WA, was modified using Modflow/MT3D to simulate the behaviour of flow along geological faults and the exponential decay of 14C using a 3D solute transport model.
Rainfall and the Wallal aquifer were assigned 14C concentrations of 100 and 10 pMC respectively. The model was run as steady state flow and transient solute transport for 15000 years, with the resulting distribution of 14C at the water table accounting for decay as well as horizontal and vertical flow (Fig 5).
Modelling results provide a proof of concept that fault conduits and elevated hydraulic heads in the Wallal aquifer can facilitate discrete discharge of older, deeper groundwater. Modelling of conservative tracers is currently being undertaken to verify these results.
a. b.
Figure 4: TEMPEST AEM conductivity-depth section for flight line L40026 (Fig 3), showing the depth of investigation (DoI) for the TEMPEST system, the location of interpreted transfer and normal faults (dashed lines), and groundwater conductivity (mS/m), for northern-most spring on L40026 (Stockyard Mangrove Spring).
a. b.
Structure and Airborne Geophysics The main structural styles from an integrated interpretation of airborne magnetics and electromagnetics resolve NW-SE transfer faults separating horst and grabens, with WSW-ENE normal faulting showing relay displacement at the Mandora Marsh valley margin, close to mound springs (Fig 3 a&b).
Mapped and sampled mound springs occur in potential zones of dilation in a transpressional setting (at the intersection of transfer and normal faults) to a depth of at least 200 meters below ground level (Fig 4).
FrOG TECH (2005) describe similar structural styles for the Canning Basin and advised reactivation of these faults was likely in the Miocene to Recent (21-5 Ma), making the faults visible in contemporary landscape and influencing the location of Quaternary and current drainage lines.
Stockyard Mangrove Spring
Spring groundwater discharge: 345 mS/m
Broome aquifer
Jarlemai Siltstone
Stockyard Mangrove Spring
DoI
POSTER PRESENTED The 3rd American Geophysical Union-Society of Exploration Geophysicists Hydrogeophysics Workshop: Imaging the Critical Zone, Stanford California 24-27 July 2017 (http://workshops.agu.org/hydrogeophysics/)
