Frieda River Limited Sepik Development Project Environmental Impact Statement Appendix 6a – Site-wide Water Balance SDP-6-G-00-01-T-003-015 Frieda River Project Site-wide Water Balance Report Prepared for Frieda River Limited Report Prepared by SRK Consulting (Australasia) Pty Ltd PNA009 August 2018 SDP-6-G-00-01-T-003-015 SRK Consulting Page ii Frieda River Project Site-wide Water Balance Frieda River Limited PO Box 2297, Fortitude Valley Business Centre Brisbane QLD 4006 SRK Consulting (Australasia) Pty Ltd Level 1, 10 Richardson Street West Perth WA 6005 e-mail: [email protected] website: asia-pacific.srk.com Tel: +61 8 9288 2000 Fax: +61 8 9288 2001 SRK Project Number PNA009 August 2018 Compiled by Peer Reviewed by Brian Luinstra John Chapman Principal Hydrogeologist Principal Consultant Email: [email protected] Author: Brian Luinstra. LUIN/CHAP/edwa PNA009_FRHEP - Water Balance_Rev3 24 August 2018 SRK Consulting Page iii Table of Contents Disclaimer .................................................................................................................................................... vi List of Abbreviations ................................................................................................................................... vii 1 Introduction and Scope of Report ............................................................................... 1 1.1 Study objectives .................................................................................................................................. 1 1.2 Statement of SRK independence ........................................................................................................ 1 2 Site Summary ............................................................................................................... 2 2.1 Location ............................................................................................................................................... 2 2.2 Meteorology ........................................................................................................................................ 5 2.2.1 Climate setting ......................................................................................................................... 5 2.2.2 Precipitation ............................................................................................................................. 6 2.2.3 Automatic weather station data ............................................................................................. 10 2.3 Hydrology .......................................................................................................................................... 11 2.4 Climate change ................................................................................................................................. 15 3 Water Balance Model Components, Inputs and Operational Logic ....................... 16 3.1 Stochastic precipitation generation ................................................................................................... 16 3.2 Evaporation and evapotranspiration ................................................................................................. 18 3.3 Catchment modelling ........................................................................................................................ 18 3.4 Open-pit development ....................................................................................................................... 20 3.5 Groundwater inflow to open-pits ....................................................................................................... 20 3.6 Water treatment ................................................................................................................................ 21 3.7 ISF ..................................................................................................................................................... 21 4 Water Balance Modelling Results ............................................................................. 23 4.1 Introduction ....................................................................................................................................... 23 4.2 Base Case: pre-embankment flows .................................................................................................. 23 4.2.1 Assessment point flows ......................................................................................................... 23 4.3 Base Case: post-embankment flows ................................................................................................ 24 4.3.1 Post-embankment flow – operational period (Model Years 0–35; FRGCP Operational Years -2 to 33) ....................................................................................................................... 24 4.3.2 Mine water management ....................................................................................................... 28 4.4 Closure period (Model Year 37-56, FRGCP Year 34–54) ................................................................ 30 4.4.1 Pit inundation ......................................................................................................................... 30 4.4.2 Closure Scenario 1: ongoing hydropower ............................................................................ 31 4.4.3 Closure Scenario 2: no hydropower ..................................................................................... 32 4.4.4 Closure Scenario 3: maintained environmental flows .......................................................... 33 5 Conclusions and Limitations .................................................................................... 35 6 References .................................................................................................................. 37 LUIN/CHAP/edwa PNA009_FRHEP - Water Balance_Rev3 24 August 2018 SRK Consulting Page iv List of Tables Table 2-1: Details of assessment point locations .......................................................................................... 5 Table 2-2: Mean annual precipitation values ................................................................................................ 7 Table 2-3: Mean monthly precipitation values for upland sites (values in mm) ............................................ 8 Table 2-4: Mean monthly precipitation values for lowland sites (values in mm) ........................................... 8 Table 2-5: Average 24 hour storm precipitation levels .................................................................................. 9 Table 2-6: Modelled PMP levels for ISF and HITEK open-pit areas ............................................................. 9 Table 2-7: Monthly average humidity (values in %) .................................................................................... 10 Table 2-8: Monthly average solar radiation (values in W/m2) ..................................................................... 10 Table 2-9: Monthly average temperature (values in degrees Celsius) ....................................................... 10 Table 2-10: Monthly average wind speed (values in m/s) ............................................................................. 10 Table 2-11: Modelled evapotranspiration and pan evaporation (mine area) ................................................ 11 Table 2-12: Mean monthly flows in Nena, Frieda and Sepik Rivers (ML/day) .............................................. 12 Table 2-13: Flows in Nena, Frieda and Sepik rivers ..................................................................................... 13 Table 2-14: Overall climate change trends ................................................................................................... 15 Table 3-1: Annual precipitation at the Lower Nena and Lower Frieda stations and from stochastic data ............................................................................................................................................ 17 Table 3-2: Parameters used in AWBM ........................................................................................................ 19 Table 3-3: Calibrated flows for AP6............................................................................................................. 19 Table 3-4: Surface areas used in open-pit contact water catchment runoff modelling ............................... 20 Table 3-5: Average daily groundwater inflow rates ..................................................................................... 21 Table 4-1: Average modelled pre-embankment daily flow at each assessment point ................................ 24 Table 4-2: Average modelled post-embankment daily flow at each assessment point for the operational period (FRGCP Years 1–33 inclusive) .................................................................... 25 Table 4-3: Average modelled post-embankment daily flow at each assessment point for the closure period with Hydroelectric power operations maintained (FRGCP years 34–54) .......... 32 Table 4-4: Average modelled post-embankment daily flow at each assessment point for the closure period with hydroelectric power terminated and all flow through the closure spillway (FRGCP years 36–56 inclusive) ................................................................................... 33 Table 4-5: Average modelled post-embankment daily flow at each assessment point for the closure period with