Accepted on 31 March 2018, doi:10.1029/2017WR021681 Confidential manuscript submitted to Water Resource Research The influence of syn-depositional macropores on the hydraulic 1 integrity of thick alluvial clay aquitards 2 Wendy A. Timms 1 , 2 , R. Ian Acworth 2 , 3 , Richard A. Crane 1 , 4 , Christoph H. Arns 5 , Ji-Youn Arns 6 , 3 Dayna E. McGeeney 2 , 3 , Gabriel C. Rau 2 , 3 , Mark O. Cuthbert 2 , 7 4 1 School of Mining Engineering, UNSW Sydney, Australia 5 2 Connected Waters Initiative Research Centre, UNSW Sydney, Australia 6 3 Water Research Laboratory, School of Civil and Environmental Engineering, UNSW Sydney, Australia 7 4 Camborne School of Mines, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Penryn, United 8 Kingdom 9 5 School of Petroleum Engineering, UNSW Sydney, Australia 10 6 Department of Applied Mathematics, Research School of Physics and Engineering, Australian National University, Canberra, 11 Australia 12 7 School of Engineering, Cardiff University, United Kingdom 13 Key Points: 14 • Syn-depositional macropores generated in a palaeo soil can increase pore connectivity and 15 therefore the vertical hydraulic conductivity. 16 • Syn-depositional macropores are present at greater depths than post-depositional features 17 which are more prevalent in the near surface. 18 • The scale of the macropores is of the order of mm and likely represents palaeo root chan- 19 nels and/or biological pathways. 20 Corresponding author: Wendy Timms, w.timms@unsw.edu.au –1–