Onshore natural gas water science studies The Gippsland groundwater model Technical report June 2015 Authors: Craig Beverly (DEDJTR), Mark Hocking (DEDJTR), Xiang Cheng (DEDJTR), Cassady O’Neil (DEDJTR), Ralf Schroers (DEDJTR) and Simon Baker (DELWP). Acknowledgements The authors acknowledge Jane McInnes (DEDJTR) and Terry McLean (DEDJTR) for their contribution to data collation, quality control, modelling and map production. Independent review was provided by: Professor Rae Mackay, Director, Geotechnical and Hydrogeological Engineering Group, Federation University Australia Professor Dayanthi Nugegoda, Ecotoxicology, School of Applied Science, RMIT University Professor Craig Simmons, Director, National Centre for Groundwater Research and Training, Flinders University. Onshore natural gas water science studies Contents Figures ................................................................................................................................................................ 6 Tables ............................................................................................................................................................... 10 Executive summary .................................................................................................................... 11 1 Introduction ........................................................................................................................ 13 1.1 Project background................................................................................................................................. 13 1.2 Project objectives ................................................................................................................................... 14 1.3 Model specification ................................................................................................................................. 14 1.4 Project duration ...................................................................................................................................... 15 1.5 Existing models ...................................................................................................................................... 15 2 Hydrogeological setting .................................................................................................... 29 2.1 Study area .............................................................................................................................................. 29 2.2 Climate ................................................................................................................................................... 31 2.3 Topography ............................................................................................................................................ 37 2.4 Land use ................................................................................................................................................. 41 2.5 Soil .......................................................................................................................................................... 43 2.6 Hydrology ............................................................................................................................................... 45 2.7 Flooding .................................................................................................................................................. 48 2.8 Surface water and groundwater interactions .......................................................................................... 53 2.9 Hydrogeology ......................................................................................................................................... 61 2.10 Current groundwater development ......................................................................................................... 65 2.11 Dominant aquifers .................................................................................................................................. 66 2.12 Schematic conceptualisation .................................................................................................................. 66 3 Numerical model design.................................................................................................... 69 3.1 Modelling approach ................................................................................................................................ 69 3.2 Data sources .......................................................................................................................................... 69 3.3 Groundwater model layer extents .......................................................................................................... 70 3.4 Groundwater model layer boundary conditions ...................................................................................... 72 3.5 Groundwater model layer parameter attribution ..................................................................................... 72 3.6 Model complexity .................................................................................................................................... 94 3.7 Allowance for temperature and density .................................................................................................. 95 The Gippsland groundwater model 3 Onshore natural gas water science studies 3.8 Allowance for faults ................................................................................................................................ 95 3.9 Model recharge ....................................................................................................................................... 95 3.10 Model evapotranspiration ....................................................................................................................... 95 3.11 Model rivers and drains .......................................................................................................................... 96 3.12 Model groundwater extractions .............................................................................................................. 99 3.13 Model simulation period ....................................................................................................................... 108 3.14 Model stress periods ............................................................................................................................ 108 3.15 Steady-state model conditions ............................................................................................................. 108 3.16 Transient model initial conditions ......................................................................................................... 108 4 Model calibration criteria ................................................................................................. 109 4.1 Key groundwater observation bores ..................................................................................................... 111 4.2 Baseflow estimates............................................................................................................................... 113 4.3 Manual calibration ................................................................................................................................ 113 4.4 Automated calibration ........................................................................................................................... 113 4.5 Sensitivity analysis ............................................................................................................................... 119 5 Steady-state model calibration ....................................................................................... 120 5.1 Mass balance ....................................................................................................................................... 123 5.2 Calibration statistics.............................................................................................................................. 123 5.3 Depth to watertable and potentiometric surfaces ................................................................................. 125 6 Transient model calibration ............................................................................................ 129 6.1 Calibrated model aquifer parameterisation .......................................................................................... 129 6.2 Mass balance ....................................................................................................................................... 130 6.3 Calibration statistics.............................................................................................................................. 131 6.4 Spatial residual error ............................................................................................................................ 133 7 Model sensitivity .............................................................................................................. 138 8 Model assumptions ......................................................................................................... 141 9 Model fit for purpose ....................................................................................................... 142 10 Scenario modelling .........................................................................................................