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Perth Shallow Groundwater Systems Investigation Lexia Wetlands Government of Western Australia Department of Water Looking after all our water needs Perth Shallow Groundwater Systems Investigation Lexia Wetlands Hydrogeological record series Report no. HG44 May 2011 Perth Shallow Groundwater Systems Investigation Lexia Wetlands Looking after all our water needs Department of Water Hydrogeological record series Report no. HG44 May 2011 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 2011 May 2011 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. ISSN 1329-542X (print) ISSN 1834-9188 (online) ISBN 978-1-921736-44-5 (print) ISBN 978-1-921736-45-2 (online) Acknowledgements The Department of Water would like to thank Stuart Richardson and team from Sinclair Knight Merz for their contribution to this report. This project was part funded by the Australian Government under its $12.9 billion Water for the Future plan. For more information about this report, contact Sandie McHugh, Water Resource Assessment Branch ([email protected]). Recommended reference DoW 2011. Perth Shallow Groundwater Systems Investigation: Lexia Wetlands, Western Australia Department of Water, Hydrogeological record series no. HG44. Disclaimer This document has been published by the Department of Water. Any representation, statement, opinion or advice expressed or implied in this publication is made in good faith and on the basis that the Department of Water and its employees are not liable for any damage or loss whatsoever which may occur as a result of action taken or not taken, as the case may be in respect of any representation, statement, opinion or advice referred to herein. Professional advice should be obtained before applying the information contained in this document to particular circumstances. This publication is available at our website <www.water.wa.gov.au> or for those with special needs it can be made available in alternative formats such as audio, large print, or Braille. Perth Shallow Groundwater Systems Investigation Hydrogeological Record, no. HG 44 Contents Preface ....................................................................................................................... vi Summary ................................................................................................................... vii 1 Context and objectives ............................................................................................ 1 2 Background ............................................................................................................. 2 2.1 Location and climate ........................................................................................................... 2 2.2 Geology and geomorphology ............................................................................................. 2 2.3 Hydrogeology .................................................................................................................... 10 2.4 Previous studies ............................................................................................................... 13 2.5 Ecological value ................................................................................................................ 15 2.6 Cultural significance ......................................................................................................... 23 2.7 Land and water management ........................................................................................... 23 3 Investigation program ............................................................................................ 25 3.1 Background ....................................................................................................................... 25 3.2 Bore construction .............................................................................................................. 25 3.3 Acid sulfate soils testing ................................................................................................... 26 3.4 Water monitoring and sampling program ......................................................................... 26 3.5 Data accuracy and precision ............................................................................................ 27 4 Geology ................................................................................................................. 29 4.1 Local geology and aquifer setting ..................................................................................... 29 4.2 Acid sulfate soils ............................................................................................................... 30 5 Hydrogeology ........................................................................................................ 38 5.1 Groundwater occurrence at the Lexia Wetlands .............................................................. 38 5.2 Groundwater flow.............................................................................................................. 38 5.3 Interaction with the regional flow system ......................................................................... 41 5.4 Water level trends ............................................................................................................. 44 5.5 Surface water–groundwater interaction inferred from groundwater level data ................ 46 5.6 Influence of land and water use on groundwater conditions at the Lexia Wetlands ........ 46 5.7 Hydrogeochemistry ........................................................................................................... 49 5.8 Main findings ..................................................................................................................... 70 6 Implications for ecological values and management recommendations ................ 75 6.1 Monitoring infrastructure ................................................................................................... 75 6.2 Summary wetland conceptualisation ................................................................................ 75 6.3 Land and water use .......................................................................................................... 77 6.4 Soil and groundwater quality implications ........................................................................ 79 6.5 Management considerations ............................................................................................ 80 Appendices ................................................................................................................ 81 Shortened forms ........................................................................................................ 98 Glossary .................................................................................................................... 99 References .............................................................................................................. 103 Department of Water iii Perth Shallow Groundwater Systems Investigation Hydrogeological Record, no. HG44 Appendices Appendix A – Bore construction diagrams ..................................................................... 82 Appendix B – Historical groundwater elevation contours ............................................... 88 Appendix C – Sampling methods and analysis.............................................................. 90 Appendix D – Water quality time series data ................................................................. 95 Figures Figure 1 Location of Lexia Wetlands ........................................................................ 4 Figure 2 Annual rainfall data and trends (period 1938–2009) .................................. 5 Figure 3 Regional geology around Lexia Wetlands .................................................. 6 Figure 4 Regional geological cross-section .............................................................. 6 Figure 5 Regional groundwater elevation contours and inferred flow directions..... 12 Figure 6 Numerical groundwater model prediction for various scenarios ............... 15 Figure 7 Location of Lexia Wetlands basins and Ministerial criteria bores ............. 17 Figure 8 Hydrographs showing current Ministerial criteria and base elevation ....... 18 Figure 9 Hydrographs showing revised EWRs and base elevation ........................ 22 Figure 11 Location of SGS monitoring bores and wetland bore locations ............... 26 Figure 12 Cross-section using SGS stage 2 investigation data ............................... 29 Figure 13 Field pH measurements at LXA_Ec and LXA_Wc) ................................. 32 Figure 14 Actual acidity as indicator of net acidity ................................................... 36 Figure 15 Time series water level data from SGS bores ......................................... 39 Figure 16 Groundwater elevation contours in March 2009 ....................................... 40 Figure 17 Groundwater elevation contours in September 2009 ............................... 41 Figure 18 Head differences between the Mirrabooka and Superficial
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