Groundwater and Surface Water Connectivity in Tasmania Preliminary Assessment and Risk Analysis Department of Primary Industries, Parks, Water and Environment Groundwater and Surface Water Connectivity in Tasmania Preliminary Assessment and Risk Analysis December 2011 Copyright Notice Material contained in the report provided is subject to Australian copyright law. Other than in accordance with the Copyright Act 1968 of the Commonwealth Parliament, no part of this report may, in any form or by any means, be reproduced, transmitted or used. This report cannot be redistributed for any commercial purpose whatsoever, or distributed to a third party for such purpose, without prior written permission being sought from the Department of Primary Industries, Parks, Water and Environment, on behalf of the Crown in Right of the State of Tasmania. Disclaimer Whilst the Department of Primary Industries, Parks, Water and Environment has made every attempt to ensure the accuracy and reliability of the information and data provided, it is the responsibility of the data user to make their own decisions about the accuracy, currency, reliability and correctness of information provided. The Department of Primary Industries, Parks, Water and Environment, its employees and agents, and the Crown in the Right of the State of Tasmania do not accept any liability for any damage caused by, or economic loss arising from, reliance on this information. Preferred Citation Sheldon, R. (2011). Groundwater and Surface Water Connectivity in Tasmania: Preliminary Assessment and Risk Analysis. Water and Marine Resources Division, Department of Primary Industries, Parks, Water and Environment, Hobart. The Department of Primary Industries, Parks, Water and Environment (DPIPWE) The Department of Primary Industries, Parks, Water and Environment provides leadership in the sustainable management and development of Tasmania’s natural resources. The Mission of the Department is to support Tasmania’s development by ensuring effective management of our natural resources. The Water and Marine Resources Division provides a focus for water management and water development in Tasmania through a diverse range of functions, including implementing the Water Management Act 1999 and the National Water Initiative; design of policy and regulatory frameworks to ensure sustainable use of surface water and groundwater resources; monitoring, assessment and reporting on the condition of the State’s freshwater resources; and providing regulatory and policy support for water infrastructure development projects. Groundwater and Surface Water Connectivity in Tasmania Executive Summary This report collates existing connected water information and provides a first pass risk assessment of water development on the connectivity of Tasmania’s water resources. It identifies key areas within regions and catchments for further assessment, planning and second pass risk assessments. Groundwater-surface water interaction has been recognised as a key issue at State and National levels, however understanding and appreciation of connected water in Tasmania is in its infancy. This report reviews existing information on the interaction of groundwater and surface water and compiles new information to increase our understanding of connected water resources in Tasmania. Understanding the nature of groundwater-surface water interaction will allow the development of effective strategies to manage these interactions, and the development of integrated water management plans for key catchments. Previous connected water studies (e.g. Tasmanian Sustainable Yields Project, Tasmanian Groundwater Models) are reviewed and results summarised. Previous baseflow separation analyses are collated and new analysis undertaken in order to determine the various levels of connectivity in catchments across Tasmania. The results of the Lyne and Hollick digital filter method undertaken for the Sustainable Yields Project are collated as are the baseflow indices acquired as part of the Groundwater Modelling Project. A new tracer approach using river conductivity and flow from selected stream gauges was used to compare baseflow index relationships for Tasmanian catchments. Connected water regions (regions with similar connected water behaviour) were developed for Tasmania, then classified and characterised. Various regionalisations were reviewed and three selected (surface water, physiography, and hydrogeology) for input to a GIS-based analysis. Thirteen regions in all resulted from the approach. Once developed, these regions were characterised using existing spatial information and classified by applying the recently developed classification system included in the National Water Commission’s Groundwater/Surface Water Connectivity Guidelines Project. Tasmania’s connected water regions fitted into four classes of connectivity, with Karst and Coastal Sands regarded as the most highly connected, followed by Northwest Basalt Plateaus and Valleys, and Basins. All of Tasmania’s water resources are however considered to be connected; only the level of connectivity varies across the state. These regions were then used as inputs to a connected water risk assessment. The risk assessment was undertaken in two parts: the first assessed the sustainability of current water extraction across the state (i.e. current surface water and groundwater extraction relative to water availability – the risk of over/double allocation); the second assessed the risk of current water development on the connectivity of Tasmania’s water resources (i.e. the risk posed to surface water resources from groundwater development, and vice versa). This assessment confirmed our knowledge of some of our key water risk areas and priorities for management, however it also highlighted some high risk areas of the state which have previously gone unnoticed. Parts of the highly connected water regions were determined to be priorities for ongoing connected water assessments and for the inclusion of provisions to manage connected water in water management plans. DPIPWE M:\WRM_Water_Resources\WWM_Water_Mgmt\WWM_Groundwater\GW_SW Project\Deliverables\Reg_RA\Final_RegRA.docx PAGE i Groundwater and Surface Water Connectivity in Tasmania Contents 1. Introduction 4 1.1. Scope 4 1.2. Objectives 5 2. Groundwater and Surface Water Connectivity 6 2.1. What is Groundwater and Surface Water Connectivity? 6 2.2. Why Should We Manage Connectivity? 7 3. Connected Water Assessments 8 3.1. Previous Studies 8 3.1.1. Tasmanian Sustainable Yields Project 8 3.1.2. Development of Models for Tasmanian Groundwater Resources Project 12 3.2. Concurrent Investigations 16 3.3. Baseflow Separation 16 3.3.1. Lyne and Hollick Filter Method 16 3.3.2. Tracer Method Using River EC 25 3.3.3. Comparison of Baseflow Separation Studies 31 3.4. Key Findings for Tasmania’s Connected Water Resources 33 4. Connected Water Regionalisation, Classification and Characterisation 34 4.1. Review of Relevant Regionalisations 34 4.1.1. Connected Water Regionalisation for Tasmania 34 4.2. Connected Water Classifications 40 4.2.1. Connected Water Classification for Tasmania 40 4.3. Connected Water Characterisation 47 4.4. Key Findings and Recommendations for Tasmania’s Connected Water Regions 50 5. Connected Water Risk Assessment 52 5.1. Previous Water Extraction Sustainability Analyses 52 5.2. Risk Assessment Approach 56 5.3. Part 1: Double Allocation/Over Allocation Risk Assessment 58 5.3.1. Input Layers 58 5.3.2. Risk Analysis 62 5.3.3. Output Layers 63 5.4. Part 2: Connected Water Regions Risk Assessment 69 5.4.1. Input Layers 69 5.4.2. Risk Analysis 70 5.4.3. Output Layers 71 5.5. Priority Regions for Connected Water Management 74 5.6. Key Findings and Recommendations based on the Connected Water Risk Assessment 75 DPIPWE M:\WRM_Water_Resources\WWM_Water_Mgmt\WWM_Groundwater\GW_SW Project\Deliverables\Reg_RA\Final_RegRA.docx PAGE ii Groundwater and Surface Water Connectivity in Tasmania 6. Conclusions 78 6.1. Recommendations 80 References 83 Appendix A Summary of Groundwater and Surface Water Connectivity Knowledge for Tasmania 89 Appendix B Summary of Previous Regionalisations for Tasmania’s Resources 90 Appendix C Metadata for Connected Water Region Input Data Layers 91 Appendix D Connected Water Regional Summaries 92 Appendix E Connected Water A3 Posters 93 DPIPWE M:\WRM_Water_Resources\WWM_Water_Mgmt\WWM_Groundwater\GW_SW Project\Deliverables\Reg_RA\Final_RegRA.docx PAGE iii Groundwater and Surface Water Connectivity in Tasmania 1. Introduction Groundwater-surface water interaction has been recognised as a key issue at the State and National level. Groundwater management in Tasmania is in its infancy, as surface water sources have previously been regarded as a more visible and obvious source for agricultural, urban and industrial purposes. Groundwater extraction/pollution has not been widely recognised as a cause of degradation in surface water environments. This is not to say that groundwater extraction has been negligible. In certain high value agricultural regions groundwater extraction is likely equal to surface water extraction. The reliance of many of Tasmania’s rivers on groundwater to provide river baseflows (and the potential for double allocation of the connected water resource) has only recently been recognised. With the predicted effects of climate change, water development will increasingly focus on groundwater resources, as surface supplies are currently approaching optimum allocation. The imminent introduction