THE TENNENT DAM OPTION A report assessing various alternatives for a new Tennent Dam for future ACT water supply FINAL APRIL 2005 ACT Future Water Options Prepared By Integrated Project Team TransACT House 470 Northbourne Avenue CANBERRA ACT 2602 Property & Planning ACTEW Project No. 800845 © ACTEW Corporation Ltd This publication is copyright and contains information that is the property of ACTEW Corporation Ltd. It may be reproduced for the purposes of use while engaged on ACTEW commissioned projects, but is not to be communicated in whole or in part to any third party without prior written consent. ACT Future Water Options TABLE OF CONTENTS Executive Summary...............................................................................................................v 1 Introduction..................................................................................................................... 1 1.1 Purpose of Report ................................................................................................. 1 1.2 Water Supply in the ACT....................................................................................... 1 1.3 Think water act water Context............................................................................... 7 1.4 Study of Future Water Options.............................................................................. 8 1.5 Study Procedure ................................................................................................. 11 1.6 Contents of Report .............................................................................................. 12 2 Tennent Option Alternatives ....................................................................................... 14 2.1 Description and History of the Region................................................................. 14 2.2 Possible Dam and Virtual Tennent Alternatives................................................. 16 2.3 The Dam Alternatives.......................................................................................... 16 2.4 Virtual Tennent Alternatives ............................................................................... 20 2.5 Other Infrastructure ............................................................................................. 22 3 Planning Requirements and Approval Processes .................................................... 24 3.1 Statutory Planning and Legislation...................................................................... 24 3.1.1 Commonwealth water legislation and policy 26 3.1.2 Commonwealth planning legislation and policy 27 3.1.3 Commonwealth environmental legislation and policy 28 3.1.4 Commonwealth heritage legislation and policy 29 3.1.5 NSW legislation and policy framework 29 3.1.6 ACT legislation and policy framework 30 3.2 Canberra Planning Policies................................................................................. 33 3.3 Lease Conditions ................................................................................................ 34 3.4 Approvals Processes .......................................................................................... 35 4 Tennent Water Resources ........................................................................................... 36 4.1 Historical River Flows.......................................................................................... 36 4.2 Environmental Flows........................................................................................... 36 4.3 Water Quality ...................................................................................................... 39 4.3.1 Tennent Reservoir 40 4.3.2 Virtual Tennent – Pumping Murrumbidgee to Stromlo Treatment Plant 42 4.3.3 Virtual Tennent – Pumping from Angle Crossing to Googong 42 4.3.4 Water Quality Conclusions 42 4.4 Influence of Climate Change............................................................................... 43 4.5 Influence of Other Variables................................................................................ 44 4.6 Water Supply Outcomes for Tennent Alternatives .............................................. 44 4.6.1 Water Supply Reliability 44 Document No: 4698 - The Tennent Option i ACT Future Water Options 4.6.2 Population Growth and Other Assumptions 45 4.6.3 Analysis of the Options 46 5 Infrastructure ................................................................................................................ 48 5.1 Principal Infrastructure Considerations................................................................ 48 5.2 Large Tennent Dam - 159 GL ............................................................................. 48 5.2.1 Site and Geotechnical Conditions 48 5.2.2 Development Description 48 5.2.3 Construction Procedure 49 5.2.4 Operations 49 5.3 The “Virtual Tennent ”: Angle Crossing to Googong ........................................... 50 5.3.1 Site and Geotechnical Conditions 50 5.3.2 Development Description 50 5.3.3 Construction Procedure 50 5.3.4 Operations 51 6 Environmental Considerations.................................................................................... 52 6.1 Changes in Sediment Transport.......................................................................... 52 6.1.1 Dam Alternatives 52 6.1.2 Virtual Tennent alternatives 52 6.1.3 Burra Creek discharge 52 6.2 Effects on Fish and Crayfish................................................................................ 53 6.2.1 Current situation 53 6.2.2 Endangered and threatened species and communities 55 6.2.3 Fish Migration 55 6.2.4 Impacts on Fish and Crayfish 56 6.2.5 Further Design and Investigation 56 6.3 Effects on Aquatic Ecology.................................................................................. 57 6.3.1 Water resource Audits of Gudgenby and Naas Rivers 58 6.3.2 River Flow effects 58 6.3.3 Biota 59 Amphibians.............................................................................................. 59 Mammals – Platypus ............................................................................... 60 Wetlands ................................................................................................. 60 Riparian Effects ....................................................................................... 60 6.3.4 Aquatic Ecology impacts 60 6.4 Effects on Terrestrial Flora and Fauna................................................................ 62 6.4.1 Flora at the Tennent Site 62 Degraded Tablelands Dry Tussock Grasslands...................................... 62 Yellow Box-Red Gum Woodland............................................................. 62 Murrumbidgee Nortons Box Callitris Woodland ...................................... 63 Slopes and Tablelands Riparian She-oak Woodland.............................. 63 6.4.2 Endangered Ecological Communities 63 Natural Temperate Grassland ................................................................. 63 Yellow Box Red Gum Grassy Woodland................................................. 63 6.4.3 Significant plant species 64 6.4.4 Fauna and Fauna Habitats at Tennent 66 Significant Animal Species ...................................................................... 66 6.4.5 Potential Impacts on Flora and Fauna 68 Document No: 4698 - The Tennent Option ii ACT Future Water Options 7 Human Environment .................................................................................................... 70 7.1 Heritage............................................................................................................... 70 7.1.1 Indigenous Heritage 70 7.1.2 European Heritage 71 7.2 Recreation........................................................................................................... 72 7.3 Amenity ............................................................................................................... 73 7.4 Public Health ....................................................................................................... 74 7.5 Energy and Greenhouse Gas Emissions ............................................................ 75 7.6 Crown Leaseholders ........................................................................................... 77 8 Economic Implications ................................................................................................ 81 8.1 Economic Framework ......................................................................................... 81 8.2 Costs to Households ........................................................................................... 82 8.3 Other Costs of Restrictions ................................................................................. 84 8.4 Overall Costs....................................................................................................... 85 8.5 Implications for Tennent Alternatives .................................................................. 88 9 Risk Assessment.......................................................................................................... 90 9.1 Risk Assessment Results.................................................................................... 90 9.2 Control Measures................................................................................................ 91 10 Sustainability Assessment............................................................................... 92 10.1 Sustainability Framework ...................................................................................