Government of Western Australia Department of Water Looking after all our water needs Groundwater recharge from the Gascoyne River, Western Australia Hydrogeological record series Report no. HG 32 May 2009 Groundwater recharge from the Gascoyne River, Western Australia Wade John Dodson (1) (1)Formerly of Department of Water Department of Water Hydrogeological record series Report no. HG 32 May 2009 Department of Water 168 St Georges Terrace Perth Western Australia 6000 Telephone +61 8 6364 7600 Facsimile +61 8 6364 7601 www.water.wa.gov.au © Government of Western Australia 2009 May 2009 This work is copyright. You may download, display, print and reproduce this material in unaltered form only (retaining this notice) for your personal, non-commercial use or use within your organisation. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. Requests and inquiries concerning reproduction and rights should be addressed to the Department of Water. National Library of Australia Cataloguing-in-Publication The recommended reference for this publication is: Dodson, Wade John 2009, Groundwater recharge from the Gascoyne River, Western Australia, Western Australia Department of Water, Hydrogeological record series HG 32. ISSN 1329-542X (print) ISSN 1834-9188 (online) ISBN 978-1-921508-59-2 (print) ISBN 978-1-921508-60-8 (online) Acknowledgements The author would like to thank Dr Angus Davidson, Mr Chris O’Boy and Dr Binh Anson for their support. For more information about this report, contact Section Manager, Groundwater Assessment. Cover photo: Gascoyne River, Western Australia Groundwater recharge from the Gascoyne River, Western Australia Hydrogeological record series, no. HG 32 Contents Abstract .......................................................................................................................ix 1 Introduction ............................................................................................................1 1.1 Historical setting ............................................................................................1 1.2 Location .........................................................................................................3 1.3 Climate ..........................................................................................................3 1.4 Physiography .................................................................................................6 1.4.1 Drainage ..........................................................................................10 1.5 Vegetation ....................................................................................................10 1.6 Land use ......................................................................................................11 1.7 Water supply ................................................................................................11 1.8 Previous investigations ................................................................................13 1.8.1 Geology ...........................................................................................13 1.8.2 Hydrogeology ..................................................................................13 1.8.3 Groundwater modelling ...................................................................15 1.8.4 Drilling and testing ...........................................................................16 1.8.4.1 Pumping-tests ....................................................................19 1.8.4.2 Geophysical logging ..........................................................20 2 Geology ................................................................................................................22 2.1 Geological setting ........................................................................................22 2.1.1 Toolunga Calcilutite .........................................................................23 2.1.2 Cardabia Calcarenite .......................................................................23 2.1.3 Older alluvium ..................................................................................23 2.1.4 Riverbed sand .................................................................................25 2.2 Depositional environment ............................................................................26 3 Hydrology .............................................................................................................28 3.1 Stream gauging ...........................................................................................28 3.2 River flow and no flow probability ................................................................32 3.3 Surface water-groundwater interaction ........................................................35 3.4 Chloride in surface water .............................................................................38 3.5 Surface water salinity ..................................................................................42 Department of Water iii Hydrogeological record series, no. HG 32 Groundwater recharge from the Gascoyne River, Western Australia 4 Hydrogeology .......................................................................................................44 4.1 Groundwater occurrence .............................................................................44 4.1.1 Riverbed sand aquifer .....................................................................44 4.1.1.1 Groundwater storage .........................................................46 4.1.2 Older alluvium aquifer......................................................................46 4.1.2.1 Groundwater storage .........................................................48 4.2 Groundwater balance ..................................................................................55 4.2.1 No flow analysis ...............................................................................55 4.2.1.1 Change in riverbed sand storage ......................................56 4.2.1.2 Leakage downwards to older alluvium ..............................58 4.2.1.3 Groundwater flow in the riverbed sand ..............................59 4.2.1.4 Abstraction from riverbed sand ..........................................60 4.2.1.5 Rainfall recharge to riverbed sand .....................................61 4.2.1.6 Evapotranspiration from riverbed sand ..............................62 4.2.2 River flow flownet analysis ..............................................................63 4.2.2.1 Throughflow by groundwater hydraulics ............................64 4.2.2.2 Throughflow by chloride mass balance .............................66 4.2.2.3 Throughflow in the riverbed sand ......................................67 4.2.2.4 Throughflow in the older alluvium ......................................69 South of the river ...............................................................69 North of the river ................................................................70 4.3 Groundwater–ocean water interface ...........................................................71 4.4 Groundwater chemistry ...............................................................................72 5 Groundwater flow model ......................................................................................75 5.1 Computer code ............................................................................................75 5.2 Model construction ......................................................................................76 5.2.1 Modelling rationale ..........................................................................76 5.2.2 Model grid and layers ......................................................................77 5.2.3 Digital files for modelling..................................................................78 5.2.4 Boundary conditions ........................................................................78 5.2.4.1 Re-wetting boundary conditions ........................................80 5.2.5 Hydraulic parameters ......................................................................81 5.2.5.1 Layer codes and storage properties ..................................81 5.2.5.2 Hydraulic conductivity ........................................................82 iv Department of Water Groundwater recharge from the Gascoyne River, Western Australia Hydrogeological record series, no. HG 32 5.2.6 Model stresses ................................................................................83 5.2.6.1 Rier flow ...........................................................................83 5.2.6.2 Eapotranspiration .............................................................86 5.2.6.3 Groundwater abstraction ...................................................88 5.2.6.4 Rainfall ...............................................................................90 5.3 Calibration ...................................................................................................91 5.3.1 Sensitiity analysis ..........................................................................93 5.3.2 Verification .......................................................................................93 5.3.3 Hydrographs ....................................................................................94 5.3.4 Water balance components .............................................................96 5.3.4.1 Eapotranspiration .............................................................97