ESTIMATING THE IMPACT OF CURRENT FARM DAM DEVELOPMENT ON THE SURFACE WATER RESOURCES OF THE ONKAPARINGA RIVER CATCHMENT DWLBC Report 2002/22 Document1 Page 1 of 1 Estimating the Impact of Current Farm Dams Development on the Surface Water Resources of the Onkaparinga River Catchment Kim S Teoh Surface Water Group, Knowledge and Information Division Department of Water, Land and Biodiversity Conservation October 2003 Report DWLBC 2002/22 In collaboration with The Onkaparinga Catchment Water Management Board and SA Water Corporation Knowledge and Information Division Department of Water, Land and Biodiversity Conservation Level 11, 25 Grenfell Street, Adelaide GPO Box 2834, Adelaide SA 5001 Telephone National (08) 8226 0222 International +61 8 8226 0222 Fax National (08) 8463 3146 International +61 8 8463 3146 Website www.dwlbc.sa.gov.au Disclaimer Department for Water Land and Biodiversity Conservation 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 for Water Land and Biodiversity Conservation and its employees expressly disclaims all liability or responsibility to any person using the information or advice. © Department for Water Land and Biodiversity Conservation 2002 This work is copyright. Apart from any use as permitted under the Copyright Act 1968 (Cwlth), no part may be reproduced by any process without prior written permission from the Department for Water Land and Biodiversity Conservation. Requests and inquiries concerning reproduction and rights should be addressed to the Director, Knowledge and Information Division, Department for Water Land and Biodiversity Conservation, GPO Box 2834, Adelaide SA 5001. ISBN 0 9751462 6 2 Teoh, K.S., 2002. Estimating the Impact of Current Farm Dams Development on the Surface Water Resources of the Onkaparinga River Catchment. South Australia. Department of Water, Land and Biodiversity Conservation. Report, DWR 2002/22. Cover. FOREWORD South Australia’s natural resources are fundamental to the economic and social wellbeing of the State. One of the State’s most precious natural resources, water is a basic requirement of all living organisms and is one of the essential elements ensuring biological diversity of life at all levels. In pristine or undeveloped situations, the condition of water resources reflects the equilibrium between rainfall, vegetation and other physical parameters. Development of these resources changes the natural balance and may cause degradation. If degradation is small, and the resource retains its utility, the community may assess these changes as being acceptable. However, significant stress will impact on the ability of a resource to continue to meet the needs of users and the environment. Understanding the cause and effect relationship between the various stresses imposed on the natural resources is paramount to developing effective management strategies. Reports of investigations into the availability and quality of water supplies throughout the State aim to build upon the existing knowledge base enabling the community to make informed decisions concerning the future management of the natural resources thus ensuring conservation of biological diversity. This assessment of the impact of current farm dams development on the surface water resources of the Onkaparinga Catchment is intended to contribute to the body of knowledge that will assist the effective management of water resources within the study area. Bryan Harris A/Director, Knowledge and Information Division Department of Water, Land and Biodiversity Conservation Estimating the Impact of Current Farm Dam Development on the Surface Water Resources of the Onkaparinga River Catchment - III - Report DWLBC 2002/22 ACKNOWLEDGEMENT The writer wishes to thank the Department of Water, Land and Biodiversity Conservation, South Australian Water Corporation and Onkaparinga Catchment Water Management Board for their assistance and comments in preparing this report. Department of Water, Land and Biodiversity Conservation Jim Barratt Graham Blair David Cresswell Theresa Heneker Robin Leaney Doug McMurray Bruce Murdoch Edward Pikusa Peter Stace Kumar Savadamuthu Martha Augoustinos Craig Walker South Australian Water Corporation Glyn Ashman Arthur Bailey Rob Hughes Peter Murphy Onkaparinga Catchment Water Management Board Steve Gatti Jill Kerby Estimating the Impact of Current Farm Dam Development on the Surface Water Resources of the Onkaparinga River Catchment - IV - Report DWLBC 2002/22 CONTENTS FOREWORD ......................................................................................................................III ACKNOWLEDGEMENT .....................................................................................................IV CONTENTS.........................................................................................................................V EXECUTIVE SUMMARY...................................................................................................11 Key Findings ..................................................................................................................11 Conclusions ...................................................................................................................15 INTRODUCTION ...............................................................................................................17 Background....................................................................................................................17 Aims of the study ...........................................................................................................17 Study Approach .............................................................................................................17 CATCHMENT DESCRIPTION...........................................................................................19 HYDROLOGICAL DATA....................................................................................................22 Rainfall...........................................................................................................................22 Evaporation....................................................................................................................30 Streamflow.....................................................................................................................31 WATER HARVESTING AND USE ....................................................................................35 Public Water Supplies....................................................................................................35 Farm Dams ....................................................................................................................38 Groundwater ..................................................................................................................45 Water use ......................................................................................................................45 SURFACEWATER MODELLING ......................................................................................49 Model Construction........................................................................................................49 Calibration......................................................................................................................49 Modelling Runoff Simulations ........................................................................................54 RESULTS AND DISCUSSIONS........................................................................................60 Rainfall Runoff Relationship ..........................................................................................60 Impact of Farm Dams on Individual Catchments (1900-1998) ......................................62 Impact of Farm Dams on Natural Flows at Houlgrave Weir ..........................................72 Impact of Farm Dams at Clarendon Weir ......................................................................81 Impact of Farm Dams at Clarendon Weir ......................................................................82 Impact on the Water Supply from Mt Bold Reservoir and Clarendon weir ....................83 SUMMARY AND CONCLUSIONS ....................................................................................89 Rainfall-runoff relationship .............................................................................................89 Farm Dam Development................................................................................................89 Farm Dam Impact on Current Scenario.........................................................................89 Farm Dam Impact on Future Scenarios.........................................................................90 Estimating the Impact of Current Farm Dam Development on the Surface Water Resources of the Onkaparinga River Catchment - V - Report DWLBC 2002/22 Opportunities to Enhance Modelling Outputs ................................................................91 SI UNITS COMMONLY USED WITHIN TEXT ..................................................................92 ABBREVIATIONS COMMONLY USED WITHIN TEXT.....................................................92 REFERENCES ..................................................................................................................93 APPENDIX