TECHNICAL REPORT PRELIMINARY INVESTIGATION OF SEAWATER INTRUSION INTO A FRESH WATER COASTAL AQUIFER – LOWER SOUTH EAST 2012/01 PRELIMINARY INVESTIGATION OF SEAWATER INTRUSION INTO A FRESHWATER COASTAL AQUIFER – LOWER SOUTH EAST Saad Mustafa, Scott Slater and Steve Barnett Science, Monitoring and Information Division Department of Environment, Water and Natural Resources September, 2012 Technical Report DEWNR 2012/01 Science, Monitoring and Information Division Department of Environment, Water and Natural Resources 25 Grenfell Street, Adelaide GPO Box 2834, Adelaide SA 5001 Telephone National (08) 8463 6946 International +61 8 8463 6946 Fax National (08) 8463 6999 International +61 8 8463 6999 Website www.waterforgood.sa.gov.au Disclaimer The Department of Environment, Water and Natural Resources and its employees do not warrant or make any representation regarding the use, or results of the use, of the information contained herein as regards to its correctness, accuracy, reliability, currency or otherwise. The Department of Environment, Water and Natural Resources and its employees expressly disclaims all liability or responsibility to any person using the information or advice. Information contained in this document is correct at the time of writing. © Crown in right of the State of South Australia, through the Department of Environment, Water and Natural Resources 2012 This work is Copyright. Apart from any use permitted under the Copyright Act 1968 (Cwlth), no part may be reproduced by any process without prior written permission obtained from the Department of Environment, Water and Natural Resources. Requests and enquiries concerning reproduction and rights should be directed to the Chief Executive, Department of Environment, Water and Natural Resources, GPO Box 2834, Adelaide SA 5001. ISBN 978-1-921923-63-0 Preferred way to cite this publication Mustafa S, Slater S and Barnett S, 2012, Preliminary investigation of seawater intrusion into a freshwater coastal aquifer – Lower South East, DEWNR Technical Report 2012/01, Government of South Australia, through Department of Environment, Water and Natural Resources, Adelaide Download this document at: http://www.waterconnect.sa.gov.au/TechnicalPublications/Pages/default.aspx Department of Environment, Water and Natural Resources | Technical Report DEWNR 2012/01 ii Preliminary investigation of seawater intrusion into a freshwater coastal aquifer – Lower South East FOREWORD The Department of Environment, Water and Natural Resources (DEWNR) is responsible for the management of the State’s natural resources, ranging from policy leadership to on-ground delivery in consultation with government, industry and communities. High-quality science and effective monitoring provides the foundation for the successful management of our environment and natural resources. This is achieved through undertaking appropriate research, investigations, assessments, monitoring and evaluation. DEWNR’s strong partnerships with educational and research institutions, industries, government agencies, Natural Resources Management Boards and the community ensures that there is continual capacity building across the sector and that the best skills and expertise are used to inform decision making. Allan Holmes CHIEF EXECUTIVE DEPARTMENT OF ENVIRONMENT, WATER AND NATURAL RESOURCES Department of Environment, Water and Natural Resources | Technical Report DEWNR 2012/01 iii Preliminary investigation of seawater intrusion into a freshwater coastal aquifer – Lower South East Department of Environment, Water and Natural Resources | Technical Report DEWNR 2012/01 iv Preliminary investigation of seawater intrusion into a freshwater coastal aquifer – Lower South East CONTENTS FOREWORD ........................................................................................................................................... III SUMMARY............................................................................................................................................... 1 1. INTRODUCTION ............................................................................................................................. 2 1.1. BACKGROUND ................................................................................................................... 2 1.2. PREVIOUS WORK ............................................................................................................... 3 1.3. HYDROGEOLOGY ............................................................................................................... 4 1.4. LAND USE .......................................................................................................................... 5 1.5. GROUNDWATER DEPENDENT ECOSYSTEMS ....................................................................... 7 1.6. AIM AND OBJECTIVES ........................................................................................................ 8 2. METHODOLOGY ............................................................................................................................ 9 2.1. REGIONAL GROUNDWATER LEVEL AND SALINITY MONITORING ........................................ 9 2.2. DRILLING ........................................................................................................................... 9 2.3. GEOPHYSICAL INVESTIGATION ......................................................................................... 10 2.4. HYDROCHEMISTRY........................................................................................................... 10 2.5. INTEGRATED GROUNDWATER AND SURFACE WATER MONITORING PROGRAM .............. 12 3. RESULTS....................................................................................................................................... 14 3.1. DRILLING PROGRAM ........................................................................................................ 14 3.2. GEOPHYSICAL INVESTIGATION ......................................................................................... 14 3.3. REGIONAL WATER LEVEL MONITORING ........................................................................... 15 3.4. REGIONAL SALINITY MONITORING ................................................................................... 18 3.5. GROUNDWATER SALINITY PROFILES ................................................................................ 18 3.6. WATER CHEMISTRY ......................................................................................................... 22 3.6.1. Chemical characteristics .................................................................................................. 22 3.6.2. Oxygen and hydrogen isotopes........................................................................................ 28 3.6.3. Seawater mixing ratio ..................................................................................................... 28 3.7. CONCEPTUAL MODEL ...................................................................................................... 30 3.8. GROUNDWATER DEPENDENT ECOSYSTEMS ..................................................................... 31 3.8.1. Seawater intrusion and Sea Level Rise ............................................................................. 33 4. DISCUSSION ................................................................................................................................. 35 5. CONCLUSIONS AND RECOMMENDATIONS .................................................................................. 36 APPENDICES .......................................................................................................................................... 38 A. HYDROSTRATIGRAPHIC LOGS ........................................................................................... 38 B. GROUNDWATER AND SURFACE WATER CHEMISTRY ........................................................ 48 C. WETLANDS WITHIN THE PROJECT BOUNDARY ................................................................. 49 D. CONCEPTUAL FLOW MODELS OF CRESS CREEK, EWENS PONDS AND MIDDLEPOINT SWAMP (SKM, 2010) ....................................................................................................... 52 UNITS OF MEASUREMENT ..................................................................................................................... 54 GLOSSARY ............................................................................................................................................. 55 REFERENCES .......................................................................................................................................... 59 Department of Environment, Water and Natural Resources | Technical Report DEWNR 2012/01 v Preliminary investigation of seawater intrusion into a freshwater coastal aquifer – Lower South East CONTENTS LIST OF FIGURES Figure 1. Location of geophysical traverses (source: King and Dodds, 2002) ........................................ 4 Figure 2. Map of the study area and final location of the drilling sites ................................................. 6 Figure 3. Intensity of groundwater extraction for irrigation within and up hydraulic gradient of the study region ................................................................................................................... 7 Figure 4. Coastal spring discharge data for 8 Eight Mile Creek, Deep Creek, Piccaninnie Ponds, Cress Creek. The blue graph represents the cumulative rainfall for