Mapping of the hyporheic zone around a tidal creek using a combination of borehole logging,borehole electrical tomography and cross-creek electrical imaging,New South Wales,Australia |
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| Authors: | R I Acworth G R Dasey |
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| Institution: | (1) UNSW Groundwater Group, Water Research Laboratory, School of Civil and Environmental Engineering, King Street, 2093, Manly Vale, New South Wales, Australia,;(2) , URS Australia Pty Ltd., Level 3, 116 Miller Street, 2060, North Sydney, New South Wales, Australia, |
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| Abstract: | A combination of electrical imaging carried out across a tidal creek and borehole electrical tomography between strings of
electrodes installed in bores adjacent to the creek is used to establish the shape of the hyporheic zone beneath a tidal creek
in a sand aquifer. The interpretations provided by the data inversions are checked against fluid electrical conductivity (EC)
samples collected from bundled piezometers installed in the creek banks and from bulk EC measurements made using induction
logs in bores on the creek banks. Extensive seepage into the base of the creek is identified from the electrical image and
verified by independent measurements of hydraulic head and fluid EC. The Effective Medium Theory is used to derive values
of fluid EC from bulk resistivity measurements obtained from the inversion process. The data show an extensive zone of mixing
between seawater and rainwater recharge into the aquifer, with the shape of the hyporheic zone strongly influenced by regional
groundwater discharge and the presence of a thin layer of cemented sands at a depth of 10 m. The combined interpretation demonstrates
the importance of borehole control in the interpretation of electrical images measured from the surface over complex EC distributions.
Electronic Publication |
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| Keywords: | Coastal aquifers Geophysical methods Salt-water/fresh-water relations |
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