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The influence of syndepositional macropores on the hydraulic integrity of thick alluvial clay aquitards

Timms, Wendy A., Acworth, R. Ian, Crane, Richard A., Arns, Christoph H., Arns, Ji-Yourn, McGeeney, Dayna E., Rau, Gabriel C. and Cuthbert, Mark O. 2018, The influence of syndepositional macropores on the hydraulic integrity of thick alluvial clay aquitards, Water resources research, vol. 54, no. 4, pp. 3122-3138, doi: 10.1029/2017WR021681.

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Title The influence of syndepositional macropores on the hydraulic integrity of thick alluvial clay aquitards
Author(s) Timms, Wendy A.ORCID iD for Timms, Wendy A. orcid.org/0000-0002-6114-5866
Acworth, R. Ian
Crane, Richard A.
Arns, Christoph H.
Arns, Ji-Yourn
McGeeney, Dayna E.
Rau, Gabriel C.
Cuthbert, Mark O.
Journal name Water resources research
Volume number 54
Issue number 4
Start page 3122
End page 3138
Total pages 17
Publisher American Geophysical Union
Place of publication Washington, D.C.
Publication date 2018-04
ISSN 0043-1397
1944-7973
Keyword(s) Science & Technology
Life Sciences & Biomedicine
Physical Sciences
Environmental Sciences
Limnology
Water Resources
Environmental Sciences & Ecology
Marine & Freshwater Biology
aquitard
macropore
preferential flow
permeability
NEW-SOUTH-WALES
SOLUTE TRANSPORT
LIVERPOOL PLAINS
ELECTRICAL-RESISTIVITY
GROUNDWATER RECHARGE
FRACTURE APERTURE
TILL
AUSTRALIA
Summary Clay-rich deposits are commonly assumed to be aquitards which act as natural hydraulic barriers due to their low hydraulic connectivity. Postdepositional weathering processes are known to increase the permeability of aquitards in the near surface but not impact on deeper parts of relatively thick formations. However, syndepositional processes affecting the hydraulic properties of aquitards have previously received little attention in the literature. Here, we analyze a 31 m deep sediment core recovered from an inland clay-rich sedimentary sequence using a combination of techniques including particle size distribution and microscopy, centrifuge dye tracer testing and micro X-ray CT imaging. Subaerial deposition of soils within these fine grained alluvial deposits has led to the preservation of considerable macropores (root channels or animal burrows). Connected pores and macropores thus account for vertical hydraulic conductivity (K) of 4.2×10-1m/s (geometric mean of 13 samples) throughout the thick aquitard, compared to a matrix K that is likely < 10-10m/s, the minimum K value that was measured. Our testing demonstrates that such syndepositional features may compromise the hydraulic integrity of what otherwise appears to have the characteristics of a much lower permeability aquitard. Heterogeneity within a clay-rich matrix could also enhance vertical connectivity, as indicated by digital analysis of pore morphology in CT images. We highlight that the paleo-environment under which the sediment was deposited must be considered when aquitards are investigated as potential natural hydraulic barriers and illustrate the value of combining multiple investigation techniques for characterizing clay-rich deposits.
Language eng
DOI 10.1029/2017WR021681
Field of Research 0907 Environmental Engineering
HERDC Research category C1.1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Grant ID FT120100216
Copyright notice ©2018, The Authors
Free to Read? Yes
Use Rights Creative Commons Attribution Non-Commercial No-Derivatives licence
Persistent URL http://hdl.handle.net/10536/DRO/DU:30115013

Document type: Journal Article
Collections: School of Engineering
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Every reasonable effort has been made to ensure that permission has been obtained for items included in DRO. If you believe that your rights have been infringed by this repository, please contact drosupport@deakin.edu.au.