Australian Capital Territory Water Resources Environmental Flow Guidelines 2019 (No 2) Disallowable instrument DI2019—190 made under the Water Resources Act 2007, s 12 (Environmental flow guidelines) 1 Name of instrument This instrument is the Water Resources Environmental Flow Guidelines 2019 (No 2). 2 Commencement This instrument commences on the day after its notification day. 3 Determination of environmental flow guidelines I approve the environmental flow guidelines in schedule 1. 4 Revocation This instrument revokes the Water Resources Environmental Flow Guidelines 2019 (DI2019-37). Mick Gentleman MLA Minister for the Environment and Heritage 24 July 2019 Authorised by the ACT Parliamentary Counsel—also accessible at www.legislation.act.gov.au Schedule 1 (see cl 3) ACT WATER RESOURCES Environmental Flow Guidelines - 2019 Contents EXECUTIVE SUMMARY ............................................................................................................... 5 Purpose of environmental flows ............................................................................................ 5 Components of environmental flows ..................................................................................... 5 How environmental flows are provided ................................................................................. 6 Ecological objectives for environmental flows ....................................................................... 6 Environmental flows in water supply catchments ................................................................. 6 Environmental flows in urban catchments ............................................................................ 7 Environmental flows in other catchments ............................................................................. 7 Indigenous water—values and uses....................................................................................... 7 Flow Requirements Summary ................................................................................................ 7 1 INTRODUCTION ....................................................................................................................... 8 1.1 Background ...................................................................................................................... 8 1.2 Purpose of the guidelines ................................................................................................ 9 1.3 National responsibilities ................................................................................................... 9 1.3.1 Murray Darling Basin Plan ......................................................................................... 9 1.4 Statutory basis for environmental flows in the ACT ....................................................... 10 1.4.1 Water Resources Act ............................................................................................... 10 1.4.2 Territory Plan .......................................................................................................... 11 1.4.3 Supporting legislation and strategies ...................................................................... 11 1.4.4 National waters ....................................................................................................... 12 1.4.5 Paramount rights to Queanbeyan and Molonglo waters ........................................ 12 1.5 Review of the guidelines ................................................................................................ 13 2 DETERMINATION OF ENVIRONMENTAL FLOWS .............................................................................. 13 2.1 Basis for determination of environmental flows ............................................................ 13 2.2 Adaptive management ................................................................................................... 14 2.3 Economic and social issues ............................................................................................ 14 2.4 Water quality issues ....................................................................................................... 15 2.5 Impoundment release structures .................................................................................. 16 1 Authorised by the ACT Parliamentary Counsel—also accessible at www.legislation.act.gov.au 2.5.1 Water supply dams ................................................................................................. 16 2.5.2 Urban lakes ............................................................................................................. 16 2.5.3 Lake Burley Griffin ................................................................................................... 16 2.6 Augmentation of stream flows ...................................................................................... 17 2.6.1 Urbanisation ........................................................................................................... 17 2.6.2 Water transfers ....................................................................................................... 17 2.6.3 Waste water discharges .......................................................................................... 17 2.7 Climate change .............................................................................................................. 17 2.8 Groundwater .................................................................................................................. 19 2.8.1 ACT aquifers ............................................................................................................ 19 2.8.2 Aquifers and base flow ............................................................................................ 19 2.9 Upstream influences ...................................................................................................... 20 2.10 Types of ecosystems .................................................................................................... 21 3 ENVIRONMENTAL FLOW APPROACH ADOPTED .................................................................... 24 3.1 Techniques for calculation of flows ............................................................................... 25 3.2 Components of environmental flows ............................................................................. 26 3.2.1 Base flows ............................................................................................................... 26 3.2.2 Flooding flows ......................................................................................................... 28 3.2.3 Special purpose flows ............................................................................................. 29 3.2.4 Impoundment drawdown levels for Urban lakes ................................................... 29 3.2.5 Temporary requirements ........................................................................................ 30 3.2.6 Water supply drought flows .................................................................................... 30 3.2.7 Flow variability ........................................................................................................ 31 4 ECOLOGICAL OBJECTIVES FOR ACT AQUATIC ECOSYSTEMS ................................................. 31 5 ENVIRONMENTAL FLOWS FOR PARTICULAR ECOSYSTEMS ................................................... 32 5.1 Water supply ecosystems .............................................................................................. 32 5.1.1 Reaches upstream of all impoundments................................................................. 33 5.1.2 Reaches between impoundments used as a conduit for water supply between Corin and Bendora dams and between Bendora and Cotter dams .................................. 33 5.1.3 Base flows ............................................................................................................... 34 5.1.4 Riffle maintenance flow .......................................................................................... 34 5.1.5 Pool maintenance flow ........................................................................................... 35 5.1.6 Drought flows - stage 1 restrictions ........................................................................ 35 5.1.7 Drought flows - stage 2 or more severe restrictions ............................................... 36 5.1.8 Reaches downstream of impoundments: Downstream of Cotter Dam Downstream of Googong Dam .............................................................................................................. 36 2 Authorised by the ACT Parliamentary Counsel—also accessible at www.legislation.act.gov.au 5.1.9 Base flows downstream of Cotter Dam .................................................................. 36 5.1.10 Riffle maintenance flow ........................................................................................ 37 5.1.11 Pool maintenance flow ......................................................................................... 37 5.1.12 Requirements applying to all water supply ecosystems ....................................... 37 5.2 Natural ecosystems ........................................................................................................ 38 5.2.1 Base flows ............................................................................................................... 39 5.2.2 Flooding flows ........................................................................................................