TNG Darwin Processing Facility Outfall · Darwin NTC AWS measured data from metocean instruments...

APPENDIX O: TECHNICAL REPORT FOR HYDRODYNAMIC

MODELLING OF DISCHARGE

TNG Darwin Processing Facility Outfall Hydrodynamic Modelling Report

15 October 2019 | 13135.101.R1.Rev0


© 2019 Baird Australia Pty Ltd as Trustee for the Baird Australia Unit Trust (Baird) All Rights Reserved. Copyright in the whole and every part of this document, including any data sets or outputs that accompany this report, belongs to Baird and may not be used, sold, transferred, copied or reproduced in whole or in part in any manner or form or in or on any media to any person without the prior written consent of Baird.

This document was prepared by Baird Australia Pty Ltd as Trustee for the Baird Australia Unit Trust for Animal Plant Mineral Pty Ltd. The outputs from this document are designated only for application to the intended purpose, as specified in the document, and should not be used for any other site or project. The material in it reflects the judgment of Baird in light of the information available to them at the time of preparation. Any use that a Third Party makes of this document, or any reliance on decisions to be made based on it, are the responsibility of such Third Parties. Baird accepts no responsibility for damages, if any, suffered by any Third Party as a result of decisions made or actions based on this document.

Commercial in Confidence

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Prepared for: Prepared by:

Animal Plant Mineral Pty Ltd 3/25 The Broadway Ellenbrook WA 6069 Contact: Mitch Ladyman Phone: +61 8 6296 5155

Baird Australia Pty Ltd as Trustee for the Baird Australia Unit Trust ACN 161 683 889 | ABN 92 798 128 010 For further information, please contact Jim Churchill at +61 8 6255 5080 [email protected] www.baird.com

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Rev. Date Status Comments Prepared Reviewed Approved

A 6/09/2019 Draft Issued For Client Review RW JC JC

0 15/10/2019 Draft Final Issue RW JC JC



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Executive Summary The TNG Darwin Processing Facility Outfall Project proposes to establish the processing facility on land adjacent the Elizabeth River Bridge near Darwin in the Northern Territory. Baird Australia Pty Limited (Baird) has been engaged by Animal Plant Mineral Pty Ltd to develop a hydrodynamic modelling program to support the environmental approvals process to assess: • Dilution contours around the outfall in typical wet and dry season conditions; • Predicted mixing zones required to meet the level of ecological protection of the waters surrounding

the mixing zone (salinity and temperature); and. • Provide outputs and reporting in a format suitable to support the development of a Marine

Environmental Quality Monitoring and Management Plan to support the environmental approvals for the Project (to be completed by O2 Marine).

A summary of the metocean conditions for the Darwin Processing Facility Outfall project has been completed incorporating background studies, analysis of climate data from a Bureau of Meteorology site at Darwin NTC AWS measured data from metocean instruments deployed in Elizabeth Rvier (collected by both O2Marine in 2019 and the Department of Environment and Natural Resources between 2015 and 2017) and Darwin Harbour (upper east arm, collected by O2Marine in 2019).

The metocean summary has informed the development of the hydrodynamic model for the project, which will be the platform for the delivery of the outfall modelling scope. A range of bathymetric and topographic data sets captured through the general marine precinct for the project were utilised to establish the model.

The hydrodynamic model has been developed using the Delft3D modelling system (Deltares 2018). A regional scale model extending across the full extent of the Northern Territory coastal region is used to define boundary conditions for a local scale hydrodynamic model established over the Darwin Harbour area in a domain decomposition grid arrangement with increasing resolution from offshore into the Harbour. The local scale model has been setup and validated for 2D (depth-averaged) and 3D sigma-layer model configurations.

The validation of the hydrodynamic model for representative four-week periods in the Wet Season and the Dry season against the measured data shows good validation metrics for water level, depth averaged current velocity and direction, as well as depth dependent current velocity and direction. The validation of the hydrodynamic model system confirms it is accurately reproducing the general hydrodynamic conditions for the Darwin Harbour project area and provides confidence the model can be applied in the outfall modelling studies to follow.



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Table of Contents

1. Introduction ............................................................................................................................. 5

1.1 Background 5

1.2 Project Overview 5

1.3 Hydrodynamic Modelling Scope 6

2. Background Information ........................................................................................................ 7

2.1 Measured Data Sources 7

2.1.1 Data Summary – Site Specific Data 7

2.1.2 Bureau of Meteorology Data 8

3. Hydrodynamic Processes .................................................................................................. 10

3.1 Bathymetric Features 10

3.2 Oceanographic Influences on Hydrodynamics 11

3.2.1 Tides 11

3.2.2 Water Level 11

3.2.3 Currents 11

3.3 Meteorological Data 16

3.3.1 Winds 16

3.3.2 Rainfall 18

3.4 Water Quality Processes Overview 19

4. Hydrodynamic Model Setup ............................................................................................... 26

4.1 Model System 26

4.2 Model Domain 26

4.2.1 Regional Scale Model 26

4.2.2 Local Scale Model 27

4.3 Model Setup 29

4.3.1 Bathymetry 29

4.3.2 Boundary Conditions 30



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4.4 Representative Seasonal Scenarios Modelled 31

4.4.1 Wet Season 31

4.4.2 Dry Season 32

5. Hydrodynamic Model Validation ........................................................................................ 33

5.1 Validation of Regional Model 33

5.2 Validation of Local Model 34

5.2.1 Hydrodynamic Model Validation 34

5.2.2 Model Metrics -Statistical Descriptions 38

5.2.3 Model Validation – Water Levels and Currents 39

5.2.4 Spatial Current Fields 40

5.2.5 2D and 3D Model Comparisons 41

6. Conclusions ......................................................................................................................... 46

7. References ............................................................................................................................ 49

Tables Table 2.1: Data Summary - Metocean Data ....................................................................................................... 7

Table 2.2: Data Summary - Site Specific Data ................................................................................................... 8

Table 3.1: Darwin Harbour Tidal Planes (Darwin NTC AWS, MGA 700647E 8620547S) ............................ 11

Table 3.2: Exceedence Table – Elizabeth River Measured Data. Depth average current speed and direction over the period 27 March 2019 to 22 May 2019 ................................................................................ 14

Table 3.3: Exceedence Table – Darwin East Arm Measured Data. Depth average current speed and direction over the period 22 May 2019 to 24 July 2019.................................................................................... 15

Table 3.4: Darwin Mean Rainfall Data (BoM 2019) .......................................................................................... 18

Table 3.5: Temperature Statistics – Analysis of DENR data from Elizabeth River, collected between 2015 and 2017 .............................................................................................................................................................. 19

Table 3.6: Salinity Statistics – Analysis of DENR data from Elizabeth River, collected between 2015 and 2017 ..................................................................................................................................................................... 21

Table 3.7: Temperature Statistics – Analysis of DENR data from Darwin Harbour Pt 2 (707429.9, 8617860 MGA94), collected between 1986 and 2018 ..................................................................................................... 23



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Table 3.8: Salinity Statistics – Analysis of DENR data from Darwin Harbour Pt 2 (707429.9, 8617860 MGA94), collected between 1986 and 2018 ..................................................................................................... 24

Table 4.1: Delft Flow Model setup summary ..................................................................................................... 28

Table 5.1: Model Metrics for water level, depth-averaged current velocity and direction .............................. 39

Table 6.1: Model Metrics for water level, depth-averaged current velocity and direction .............................. 47

Figures Figure 2.1: Measured Data Locations ................................................................................................................. 9

Figure 3.1: Bathymetric data coverage across the TNG Darwin Outfall local scale model domain ............. 10

Figure 3.2: Measured Data from Darwin Inner Harbour Aquadopp, May to July 2019. Time series depth averaged current velocity and direction with associated water level. .............................................................. 12

Figure 3.3: Measured Data from Darwin Inner Harbour Aquadopp, May to July 2019. Time series depth averaged current velocity and direction with associated water level. .............................................................. 13

Figure 3.4: Current speed rose plot in Elizabeth River, based on measured data collected by O2Marine over the period 27 March 2019 to 22 May 2019 . ............................................................................................. 14

Figure 3.5: Current speed rose plot in Darwin Inner Harbour, based on measured data collected by O2 in the dry season of 2019. ...................................................................................................................................... 15

Figure 3.6: Measured current data roses at the location of data capture. Sites are shown at Darwin Harbour East Arm location to the north west and Elizabeth River to the south east .................................................... 16

Figure 3.7: Wind Rose plots by month based on 20 years analysis of the measured data from Darwin BoM NTC AWS (1999-2019) ..................................................................................................................................... 17

Figure 3.8: Wind Rose for Dry Season (left) and Wet Season (Right) based on analysis of Darwin BoM NTC AWS data (1999-2019) .............................................................................................................................. 18

Figure 3.9: Temperature measured at Elizabeth River by the DENR between September 2015 and November 2017, covering two dry seasons and two wet seasons ................................................................. 20

Figure 3.10: Temperature measured at Elizabeth River by the DENR between September 2015 and November 2017, covering two dry seasons and two wet seasons ................................................................. 22

Figure 3.11: INPEX Channel Island water quality monitoring site ‘CHI’ in Middle Arm and DENR water quality monitoring site Darwin Harbour Pt 2 ...................................................................................................... 23

Figure 3.12: Measured Temperature variation between August 2012 and August 2014 at the Channel Island Site in Middle Arm (Source, INPEX 2014 Ichthys Project LNG Project Nearshore Environmental Monitoring Program report). ............................................................................................................................... 24



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Figure 3.13: Measured Salinity variation between August 2013 and August 2014 at the Channel Island Site in Middle Arm (Source, INPEX 2014 Ichthys Project LNG Project Nearshore Environmental Monitoring Program report). .................................................................................................................................................. 25

Figure 4.1: Regional Delft-FM model grid Extent and bathymetry. ................................................................. 27

Figure 4.2: Local Hydrodynamic Model - Domain Decomposition Grid setup ................................................ 29

Figure 4.3: Bathymetry Grid for Local Scale Model (Datum m MSL Darwin Harbour) .................................. 30

Figure 4.4: Local Model Domain (Yellow Boundaries) nested inside Regional Model Domain Flexible Mesh Grid (shown in orange) ....................................................................................................................................... 31

Figure 5.1: Regional Model Tidal Validation at nearby Port locations ............................................................. 33

Figure 5.2: Comparison of Elizabeth River Location Measured vs Modelled Data for Water level and Depth Averaged Current. Dry Season Validation Period, 1 April 2019 – 30 April 2019. .......................................... 35

Figure 5.3: Comparison of Elizabeth River Location Measured vs Modelled Data for Water level and Depth Averaged Current. Wet Season Validation Period, 5 January 2016 – 5 February 2016. .............................. 36

Figure 5.4: Comparison of Darwin Harbour Location Measured vs Modelled Data for Water level and Depth Averaged Current. Dry Season Validation Period, 20 June 2019 to 20 July 2019 ........................................ 37

Figure 5.5: Local Model Grids – Flood Tide for Large Spring Tide Case (06 Apr 2019 1900UTC) .............. 40

Figure 5.6: Local Model Grids – Ebb Tide for Large Spring Tide Case (07 Apr 2019 0030UTC) ................ 41

Figure 5.7: Comparison of modelled 2D and 3D current speed timeseries data from the Darwin Harbour East Arm Location ............................................................................................................................................... 42

Figure 5.8: Comparison of 3D current speed and direction modelled and measured data from the Darwin Harbour Aquadopp .............................................................................................................................................. 42

Figure 5.9: Comparison of Darwin Harbour Location Measured vs Modelled Data for Water level and Depth Averaged Current ................................................................................................................................................ 43

Figure 5.10: Comparison of Darwin Harbour Location Measured vs Modelled Data for Water level and bottom layer currents .......................................................................................................................................... 44

Figure 5.11: Comparison of Darwin Harbour Location Measured vs Modelled Data for Water level and bottom layer currents .......................................................................................................................................... 45



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1. Introduction

1.1 Background

Animal Plant Mineral Pty Ltd (APM) are preparing the environmental approval for TNG Limited (TNG) who have submitted a Notice of Intent (NOI) to the Northern Territory Environment Protection Authority (NT EPA) and Department of Lands Planning and Environment (DLPE) to construct and operate the Darwin Processing Facility (processing facility).

TNG proposes to establish the Processing Facility on land adjacent the Elizabeth River Bridge. Land to the north, south and west contains intertidal areas and mangrove forests that connect the site to the Elizabeth River and Darwin Harbour, and have been zoned for Conservation.

The Processing Facility will process magnetite concentrate to produce: • vanadium pentoxide - for use in steel, non-ferrous alloys, chemicals, catalysts and energy storage

(vanadium redox batteries); • titanium dioxide pigment - for use in paint, plastics, paper and inks; and • pig iron - for use in steel making.

The three products will be exported through the Port of Darwin’s East Arm Wharf to international customers.

The Processing Facility outfall will discharge wastewater into the Darwin Harbour system, with the exact location to be determined. Based on discussions with APM the wastewater will be released at a higher temperature than the ambient receiving waters in the Darwin Harbour system and the discharge water will be at a lower salinity to the ambient salinity in Darwin Harbour system.

1.2 Project Overview

The primary objective of the outfall modelling is to support the environmental approvals for the site which will be delivered by APM and O2Marine. The modelling program will examine in detail reduction in water quality around the outfall location and also consider the far-field effects of the wastewater impacts to Darwin Harbour. The program will characterise the local hydrodynamic conditions in the Elizabeth River and other locations around the project site and assist in determination of an outfall diffuser design and wastewater release strategy. The modelling program will determine: • Dilution contours around the outfall in typical wet and dry season conditions; • Predicted mixing zones required to meet the level of ecological protection of the waters surrounding

the mixing zone (salinity and temperature); and. • Provide outputs and reporting in a format suitable to support the development of a Marine


The study program by Baird is arranged to be completed in three phases which will complement the timing and delivery of the O2Marine metocean measurement campaign and Marine Environmental Quality Monitoring and Management Plan. The phases are as follows: 1. Initial hydrodynamic model development 2. Engineering design phase of diffuser design and location 3. Detailed plume modelling



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This report summarises the hydrodynamic model establishment and the validation against measured data sources from Darwin Harbour. This hydrodynamic model will provide the basis for detailed outfall modelling of the wastewater into Darwin Harbour, with analysis to support the EIS.

1.3 Hydrodynamic Modelling Scope

Baird has been engaged by APM to develop a hydrodynamic model of the Darwin region around the project site. The model system will be applied in studies to follow which will analyse the water quality and marine impacts from the processing facility outfall.

The hydrodynamic model establishment and validation is outlined in this report. The tasks for the hydrodynamic model detailed in Baird’s initial scope for APM are as follows: 1. A summary of input data will be prepared, which will draw on the Metocean summary and review of

relevant reports and documentation. 2. Application of Baird’s existing hydrodynamic model of Darwin Harbour (regional scale) and refine the

model description through the Elizabeth River area to a higher resolution around the site incorporating available bathymetry sources. Boundary conditions to input to the local scale far field hydrodynamic model will be taken from this existing validated model.

3. Local scale far field hydrodynamic model establishment (2D and 3D), inclusive of tidal flows and wind conditions. • Validation of model against measured water levels, current velocity and direction (based on data

available at kick-off and as these become available from O2Marine) • Establish representative seasonal periods of four weeks model duration to describe the typical

hydrodynamics occurring in representative periods nominally for: ο dry season ο wet season

• Reporting of key metocean characteristics at the site over the spring – neap tide cycle would be documented from the model for each seasonal period. Output to be shown as time series, graphical plots, rose plots, exceedance tables.



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2. Background Information

2.1 Measured Data Sources

The measured data sources available to the project which have been applied in the setup of the numerical model system are outlined in this section.

2.1.1 Data Summary – Site Specific Data

Table 2.1: Data Summary - Metocean Data

Dataset Description

Bathymetry

• Very detailed bathymetric surveys of Darwin Inner Harbour, undertaken between October 17 and November 7 2010 and June 24 and August 20th 2011 by iXSurvey Australia Pty Ltd for Darwin Port Corporation and Department of Lands Planning and the Department of Natural Resources, Environment, The Arts and Sport (NRETAS), in collaboration with Geoscience Australia (GA), the Darwin Port Corporation (DPC) and the Australian Institute of Marine Science (AIMS) were compiled into one dataset covering a large part of Darwin Inner Harbour, reaching down East and Middle Arm into the Elizabeth River and the Blackmore River at a resolution of 1m.

• Bathymetric survey of Darwin Outer Harbour was undertaken between May 28 and June 23 2015 by Geoscience Australia (GA) in collaboration with the Australian Institute (AIMS) and the Department of Land Resource Management (Northern Territory), covering a large extent of the outer harbour at a resolution of 1m (cut down to 10m for ease of use in this instance).

• Where required, depth data was supplemented with the recent Australian Hydrographic Service (RAN) bathymetric charts for Darwin Harbour (AUS0025 and AUS0026).

Topography

A DEM of the Darwin Region (UTM Zone 52L) has been compiled as part of a long-term collaboration between Geoscience Australia (GA), the Cooperative Research Centre for Spatial Information (CRCSI), the Departments of Climate Change and Environment and Local Governments, covering a large majority of the landward part (above 0m AHD) of the Darwin Harbour coastal region, at a resolution of 5m.

Baseline Metocean Data

Elizabeth River Aquadopp (O2) • Approximately 1.2km downstream of the Elizabeth River Bridge in

Palmerston, in 5.7m depth (MSL, MGA50 713734E, 8613513S) • Deployment covering the period 27 March 2019 – 22 May 2019 • Current speed and direction through the water column, Water Level,

Temperature Darwin Harbour Aquadopp (O2) • Approximately 1.5km offshore of the East Arm Boat Ramp, in 8.2m

depth (MSL, MGA50 707986E, 8617540S) • Deployments covering period 22 May 2019 – 24 July 2019



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Dataset Description

• Current speed and direction through the water column, Water Level, Temperature

Elizabeth River ADCP (DENR) • Approximately 1.2km downstream of the Elizabeth River Bridge in

Palmerston, in 5.7m depth (MSL, MGA50 713754 8613566) • Deployments covering November 2015 to September 2017 (some

gaps existing) • Current speed and direction through the water column, Water Level,

Temperature

Baseline Water Quality

Elizabeth River Seabird CTD (DENR) • Approximately 1.2km downstream of the Elizabeth River Bridge in

Palmerston, in 5.7m depth (MSL, MGA50 713754 8613566) • Deployments covering April 2015 to April 2016 (some gaps existing) • Temperature, Salinity, pH, DO, PAR, Turbidity, Fluorescence Darwin Harbour (Darwin Harbour Pt2) WQ logger (DENR) • Approximately 1.5km offshore of the East Arm Boat Ramp, in 8.2m

depth (MSL, MGA50 707429E, 8617859S) • Deployments covering December 1986 to October 2018 (many and

large gaps) • Salinity, NTU, Temperature, pH, TDS etc.

2.1.2 Bureau of Meteorology Data

Table 2.2: Data Summary - Site Specific Data

Dataset Description

Measured Wind Data from Darwin Airport (14072)

Data for the period 16 August 2012 to 20 May 2019 from the Darwin Station location at the Darwin Airport, northwest of the project site (MGA 705453E 8626273S) • Wind Speed / Direction data Half hourly data converted, measured 10-minute average at 10m height

Measured Tide, WQ and Wind Data from NTC AWS (IDO71014)

Data for the period 01 Jan 1991 to 31 July 2019 from the Darwin NTC AWS (including tide gauge) on Fort Hill Wharf (MGA 700647E 8620547S) • Sea Level (mAHD) • Water Temperature (degC) • Pressure (hPa) • Wind Speed (m/s) • Wind Gust (m/s) • Wind Direction (degN)

The locations of the measured metocean data is shown in Figure 2.1.



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Figure 2.1: Measured Data Locations

Darwin Airport (BOM 014027)

DENR Darwin Harbour Pt2

O2 Darwin Harbour Adopp

DENR ElizRiv01

O2 Middle Arm Adopp

Darwin NTC AWS (BOM IDO71014)

O2 Elizabeth River Adopp



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3. Hydrodynamic Processes

3.1 Bathymetric Features

Bathymetric and topographic data covering the model domain was available at high resolution (see Table 2.1 for attribution details) across the majority of the local scale modelling domain, providing an excellent description of the depths through the harbour and into its tributaries, as well as elevation over the land side. The combined survey data is shown in Figure 3.1 to the datum of Mean Sea Level (equal to m AHD in Darwin Harbour).

Figure 3.1: Bathymetric data coverage across the TNG Darwin Processing Facility Outfall local scale model domain



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The hydrographic Charts AUS025 and AUS026 have been used in this study to define any areas not described by the bathymetric and topographic data shown above, specifically the intertidal and offshore area between East Point and Lee Point, and the dredged channel and pocket reaching towards Inpex facilities based on Bladin Point.

3.2 Oceanographic Influences on Hydrodynamics

3.2.1 Tides

The astronomical tide is the periodic rise and fall of the sea surface caused by the combination of the gravitational force exerted by the moon and the Sun upon the Earth and the centrifugal force due to rotations of the Earth and moon, and the Earth and the Sun around their common centre of gravity. Tides are subject to spatial variability due to hydrodynamic, hydrographic and topographic influences.

The Darwin Processing Facility Outfall project location experiences a semi-diurnal tide (two highs and two lows a day), with an overall tidal range of 8m, a spring tidal range of about 6m, and a neap tidal range of around 3m (Cardno 2014). Tidal planes, as provided in hydrographic Charts AUS025 and AUS026, are provided in Table 3.1.

Table 3.1: Darwin Harbour Tidal Planes (Darwin NTC AWS, MGA 700647E 8620547S)

Tidal Planes Elevation (m LAT)

HAT 8.1

MHWS 7.0

MHWN 5.1

MSL 4.2

MLWN 3.3

MLWS 1.4

LAT 0.0

3.2.2 Water Level Consistent water level measurement has been taken at the Darwin NTC AWS at Fort Hill Wharf since 1991, providing a reliable and relatively long-term water level record close to the project site. In addition to this dataset, there were two instruments deployed for the project to measure the water level in the Elizabeth River and Darwin Harbour near East Arm (refer Figure 2.1 and Table 2.1).

3.2.3 Currents

Current speed and direction have been measured by the Department of Environment and Natural Resources (DENR) in the Elizabeth River over the period 2015 to 2017, providing coverage of all seasons occurring in the northern territory, including: • wet season; • wet to dry season transition; • dry season; and, • dry to wet season transition.



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Further current speed and direction measurements have been carried out by O2Marine in Elizabeth River (measured in close proximity to the data provided by DENR) and Darwin Inner Harbour, both measured with an Aquadopp Instrument, covering the periods of: • 27 March 2019 to 22 May 2019 (wet to dry Season Transition); and, • 22 May 2019 to 24 July 2019 (Dry Season) respectively.

The measured currents from the O2Marine Aquadopp within Elizabeth River (2019) show the following characteristics during the wet to dry season transition period over which it was deployed: • Depth averaged peak current speed of 0.8ms-1 - 1.0ms-1 in springs and 0.2ms-1 – 0.4ms-1 in neaps • Current direction (direction to) consistent in Ebb 290˚ - 300˚ and Flood 100˚ - 120˚ • The ebb current speeds are generally stronger than the flood current speeds

The measured currents from the O2Marine Aquadopp within Darwin Inner Harbour (East Arm) show the following characteristics during the dry season period over which it was deployed: • Depth averaged peak current speed of 0.6ms-1 - 0.7ms-1 in springs and 0.2ms-1 – 0.25ms-1 in neaps • Current direction (direction to) consistent in Ebb 240˚ - 270˚ and Flood 40˚ - 70˚ • The ebb current speeds are also generally stronger than the flood current speeds

The depth averaged current time series data from 27 March 2019 to 22 May 2019 measured by the Elizabeth River Aquadopp is shown in Figure 3.2, and from 22 May 2019 to 24 July 2019 measured by the Darwin Inner Harbour Aquadopp is shown in Figure 3.3.

Figure 3.2: Measured Data from Darwin Inner Harbour Aquadopp, May to July 2019. Time series depth averaged current velocity and direction with associated water level.



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Figure 3.3: Measured Data from Darwin Inner Harbour Aquadopp, May to July 2019. Time series depth averaged current velocity and direction with associated water level.

The current speeds and direction measured at Elizabeth River and Darwin Harbour are shown graphically in rose plots presented in Figure 3.4 and Figure 3.5 respectively. These rose plots clearly illustrate the alignment of the ebb and flood currents change from within the Elizabeth River to within Darwin Inner Harbour, reflecting the local geomorphology, further illustrated in Figure 3.7, with Elizabeth River notably more southeast - northwest aligned whilst Darwin Inner Harbour is more northeast to southwest aligned. The Elizabeth River current speeds are higher than Darwin Inner Harbour, also reflecting the local geomorphology, with flows being more constricted and funnelled through the banks of the Elizabeth River region.



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Figure 3.4: Current speed rose plot in Elizabeth River, based on measured data collected by O2Marine over the period 27 March 2019 to 22 May 2019 .

Table 3.2: Exceedence Table – Elizabeth River Measured Data. Depth average current speed and direction over the period 27 March 2019 to 22 May 2019

Current Direction (going to)

Current Speed

N

NN

E

NE

ENE

E ESE

SE

SSE S

SSW

SW

WSW

W

WN

W

NW

NN

W

Total (%)

<0.2ms-1 1.06 0.76 0.99 1.75 3.72 5.24 3.49 1.59 0.53 1.06 1.44 2.20 5.39 6.68 4.18 2.35 42.44

0.2ms-1 to

< 0.4ms-1 0.00 0.15 0.00 0.08 3.34 13.67 2.35 0.08 0.00 0.00 0.00 0.00 2.73 8.96 1.37 0.08 32.80

0.4ms-1 to

< 0.6ms-1 0.00 0.00 0.00 0.00 1.37 10.10 0.38 0.00 0.00 0.00 0.00 0.00 0.38 6.23 0.23 0.00 18.68

0.6ms-1 to

< 0.8ms-1 0.00 0.00 0.00 0.00 0.00 0.30 0.00 0.00 0.00 0.00 0.00 0.00 0.08 4.10 0.00 0.00 4.48

0.8ms-1 to 1.0ms-1

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.29 0.00 0.00 1.29

>1.0ms-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.30 0.00 0.00 0.30

TOTAL 1.06 0.91 0.99 1.82 8.43 29.31 6.23 1.67 0.53 1.06 1.44 2.20 8.58 27.56 5.77 2.43 100.00



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Figure 3.5: Current speed rose plot in Darwin Inner Harbour, based on measured data collected by O2 in the dry season of 2019.

Table 3.3: Exceedence Table – Darwin East Arm Measured Data. Depth average current speed and direction over the period 22 May 2019 to 24 July 2019

Current Direction (going to)

Current Speed

N

NN

E

NE

ENE

E ESE

SE

SSE S

SSW

SW

WSW

W

WN

W

NW

NN

W

Total (%)

<0.2ms-1 3.05 3.45 5.51 4.11 2.32 0.46 0.40 0.27 0.20 0.53 2.19 6.83 8.10 4.84 2.39 2.32 46.98

0.2ms-1 to

< 0.4ms-1 0.40 3.05 7.76 8.36 0.46 0.07 0.00 0.00 0.00 0.00 0.53 8.16 7.90 1.19 0.40 0.33 38.62

0.4ms-1 to

< 0.6ms-1 0.00 0.33 4.84 1.73 0.00 0.00 0.00 0.00 0.00 0.00 0.07 4.11 2.85 0.00 0.00 0.00 13.93

>0.6ms-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.20 0.27 0.00 0.00 0.00 0.46

TOTAL 3.45 6.83 18.12 14.20 2.79 0.53 0.40 0.27 0.20 0.53 2.79 19.31 19.11 6.04 2.79 2.65 100.00



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Figure 3.6: Measured current data roses at the location of data capture. Sites are shown at Darwin Harbour East Arm location to the north west and Elizabeth River to the south east

3.3 Meteorological Data

The nearest Bureau of Meteorology (BoM) meteorological station for the project is located at Fort Hill Wharf to the north west of the proposed outfall location options. This BOM NTC AWS site (Figure 2.1) measures water level, water temperature, air temperature, barometric pressure, wind speed, wind gust speed and wind direction for Darwin Harbour.

3.3.1 Winds

Darwin is located in the tropical north of the Northern Territory, sitting within the band of the Tropical Major Koppen Class, in the Climate Zone characterised by hot humid summers (BOM 2016); • The dry season (generally May to October) is characterised by hot temperatures, easterly to south-

easterly winds and clear and stable conditions derived from the subtropical high-pressure ridge. • In the wet season months (generally November to April) the wind climate is more active and

dominated by westerly and north-westerly winds.

Wind rose plots for each respective month of measured data from Darwin across the approximately 20-year measured dataset at the Darwin BoM NTC AWS are shown in Figure 3.7.



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Figure 3.7: Wind Rose plots by month based on 20 years analysis of the measured data from Darwin BoM NTC AWS (1999-2019)



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Based on analysis of the monthly wind data (Figure 3.7), the key periods for the wet season and dry season is summarised as follows: • Dry season – May to October • Wet season – November to April

Wind rose plots for the Dry Season months (May to October) and Wet Season months (November to April) are presented in Figure 3.8 based on analysis of the measured wind records from Darwin BoM NTC AWS over the period 1999 - 2019.

Figure 3.8: Wind Rose for Dry Season (left) and Wet Season (Right) based on analysis of Darwin BoM NTC AWS data (1999-2019)

3.3.2 Rainfall

The Darwin regional climate is classed by the Bureau of Meteorology (BoM) as ‘Equatorial Savanna’ characterised by year-round hot weather, with emphasis on a hot humid summer. Rains are delivered in the wet season by the northwest monsoonal system bringing warm moist air over the Darwin region. These systems can bring both tropical storms (lows) and tropical cyclones to the Darwin region, consistently bringing considerable rainfall and associated large volumes of fresh water to Darwin Harbour. Conditions are stable during the dry season due to the sub-tropical high-pressure ridge that sits over the region during these months. There is little cloud cover or rainfall during the dry season, with associated high rates of evaporation from water bodies during this season (BOM 2019).

Rainfall statistics from the Darwin Airport are reported in Table 3.4, showing mean rainfall data from 1941 to 2019.

Table 3.4: Darwin Mean Rainfall Data (BoM 2019)

Month J F M A M J J A S O N D Annual

Rainfall (mm) 429.4 372 314.8 101.5 21.2 1.7 1.1 4.6 15.8 70.2 143.4 251.1 1731.2



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3.4 Water Quality Processes Overview

Water quality datasets with the temporal coverage to describe water quality conditions in both wet and dry season, including salinity and temperature conditions across these seasons, are largely limited to the Elizabeth River, based on data measured by DENR between September 2015 and April 2016. A temporally sparse dataset captured sporadically between 1986 and 2018 within the outer reaches of East Arm (Darwin Harbour Pt2 in Figure 2.1) provides some indication of salinity and temperature variation between the seasons, which can be given further veracity when compared with information taken from INPEX’s 2014 Ichthys Project LNG Project Nearshore Environmental Monitoring Program report. Baird have made a request to INPEX to gain access to data measured in Darwin Harbour over the course of the INPEX project without success. Further data collection to inform temperature and salinity values over wet season and dry season in the Harbour is recommended to confirm statistics calculated from the available DENR dataset.

Temperature statistics for the Elizabeth River, calculated from data obtained from DENR, are provided in Table 3.7. Variation in temperature is higher in the dry season, with a maximum to minimum temperature range of 4.4˚C, compared to the wet season, with a maximum to minimum temperature range of 2.4˚C. This variation, as well as the general trend of warmer water temperature measured in wet season, is evident in Figure 3.9

Table 3.5: Temperature Statistics – Analysis of DENR data from Elizabeth River, collected between 2015 and 2017

Water Temperature (˚C)

Season Median Maximum Minimum 80th Percentile

95th percentile

Dry Season 28.0 32.4 22.4 30.7 31.6

Wet Season 31.8 34.2 24.3 32.3 32.7



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Figure 3.9: Temperature measured at Elizabeth River by the DENR between September 2015 and November 2017, covering two dry seasons and two wet seasons



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Salinity statistics for the outer reaches of East Arm (Darwin Harbour), calculated from data obtained from DENR, are provided in Table 3.8. Median Salinity is higher in the dry season (36.8ppt) compared to the wet season (30.8ppt). Variation in salinity is significantly higher in the wet season, with a maximum to minimum salinity range of 23.7 ppt, compared to the dry season, with a maximum to minimum salinity range of 1.8 ppt. These salinity outcomes are due to the significant freshwater inflows experienced by the Darwin Harbour during the wet season.

Table 3.6: Salinity Statistics – Analysis of DENR data from Elizabeth River, collected between 2015 and 2017

Salinity (ppt)


95th percentile

Dry Season 36.8 37.9 36.1 37.1 37.5

Wet Season 30.8 37.6 14.0 36.1 36.9



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Figure 3.10: Temperature measured at Elizabeth River by the DENR between September 2015 and November 2017, covering two dry seasons and two wet seasons



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Temperature statistics for the outer reaches of East Arm (Darwin Harbour), calculated from data obtained from DENR, are provided in Table 3.7. Variation in temperatures is significantly higher in the dry season, with a maximum to minimum temperature range of 8.8˚C, compared to the wet season, with a maximum to minimum temperature range of 4.7˚C. This variation is also seen in Figure 3.12, taken from INPEX’s 2014 Ichthys Project LNG Project Nearshore Environmental Monitoring Program report, with visual inspection showing similar temperature ranges measured at INPEX’s water quality monitoring site at Channel Island in Middle Arm (Figure 3.11).

Table 3.7: Temperature Statistics – Analysis of DENR data from Darwin Harbour Pt 2 (707429.9, 8617860 MGA94), collected between 1986 and 2018

Water Temperature (˚C)


95th percentile

Dry Season 26.9 32.7 23.9 29.7 30.8

Wet Season 31.1 32.8 28.1 31.6 32.2

Figure 3.11: INPEX Channel Island water quality monitoring site ‘CHI’ in Middle Arm and DENR water quality monitoring site Darwin Harbour Pt 2

DENR WQ Monitoring Site Darwin Harbour Pt 2

INPEX WQ Monitoring Site Channel Island (Site 1 - CHI)



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Figure 3.12: Measured Temperature variation between August 2012 and August 2014 at the Channel Island Site in Middle Arm (Source, INPEX 2014 Ichthys Project LNG Project Nearshore Environmental Monitoring Program report).

Salinity statistics for the outer reaches of East Arm (Darwin Harbour, calculated from data obtained from DENR, are provided in Table 3.8. Variation in salinity is significantly higher in the wet season, with a maximum to minimum salinity range of 16.8 ppt, compared to the dry season, with a maximum to minimum salinity range of 8.3 ppt, as expected due to the significant freshwater inflows experienced by the Darwin Harbour during the wet season. This variation is also seen in Figure 3.13, taken from INPEX’s 2014 Ichthys Project LNG Project Nearshore Environmental Monitoring Program report, with visual inspection showing similar salinity ranges measured at INPEX’s water quality monitoring site at Channel Island in Middle Arm (Figure 3.11).

Table 3.8: Salinity Statistics – Analysis of DENR data from Darwin Harbour Pt 2 (707429.9, 8617860 MGA94), collected between 1986 and 2018

Salinity (ppt)


95th percentile

Dry Season Average 35.3 39.6 31.3 36.4 36.8

Wet Season Average 32.1 37.5 20.7 35.7 36.3



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Figure 3.13: Measured Salinity variation between August 2013 and August 2014 at the Channel Island Site in Middle Arm (Source, INPEX 2014 Ichthys Project LNG Project Nearshore Environmental Monitoring Program report).



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4. Hydrodynamic Model Setup

4.1 Model System

The hydrodynamic model has been developed using the Delft3D modelling system (Deltares 2018). Delft3D is an integrated modelling suite, which simulates two-dimensional (in either the horizontal or a vertical plane) and three-dimensional flow, sediment transport and morphology, waves, water quality, and ecology and can handle the interactions between these processes.

The Delft3D system is built around modules that can be coupled to simulate specific processes. For the hydrodynamics, the FLOW module was used to simulate the flows within Darwin Harbour, and through the key project areas of interest in East Arm and the Elizabeth River. The model has been setup in 2D for validation of the hydrodynamics, with some initial 3D simulations run to investigate the efficacy of the model in describing processed occurring through the water column. Both 2D and 3D simulations will be applied in the outfall project modelling investigations.

4.2 Model Domain

For this project Baird has utilised its existing regional scale hydrodynamic model for the Northern Territory to provide boundary inputs (water levels) to a local scale model at high resolution for the Darwin coast around the project site.

4.2.1 Regional Scale Model

The regional scale model has adopted Baird’s existing Delft-Flow Flexible Mesh (D-Flow FM) model of the Northern Territory. The model extent is shown in Figure 4.1 extending across the entire northern coast of the Northern Territory and down through Darwin Harbour and into the Elizabeth River in the vicinity of the project site. The flexible mesh grid is triangular with increasing resolution shoreward and ranges from approximately 5km offshore to 500m along coastal areas. The model is driven by tidal constituents along its open boundaries with bathymetry defined from hydrographic chart data and local scale bathymetry sources where available.

The local scale model boundary conditions have been defined from the regional scale model.



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Figure 4.1: Regional Delft-FM model grid Extent and bathymetry.

4.2.2 Local Scale Model

The local scale model is established over the Darwin Harbour area with boundary conditions defined by the Regional model. The local model is setup in a domain decomposition grid arrangement to optimise the efficiency of the model performance. The outer grid extends across the Darwin Harbour area aligned with the aspect of the Harbour, extending 33km across the outer harbour, and 52km down to the harbour tributaries. The outer grid is setup on a 100m grid size, and a smaller domain within sized at 33m extends around the upper East Arm area close to the project site.

Regional Model Grid Darwin Harbour

Project Location Elizabeth River



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An overview of the local model domain is shown in Figure 4.2, with the key characteristics of the model specified in Table 4.1. The local model can be run in 2D (depth-averaged) and 3D in sigma-layer mode. The specifications for the 2D and 3D modes are presented in Table 4.1.

Table 4.1: Delft Flow Model setup summary

Feature Description

Grid size / type Domain Decomposition (DD) - Regular Grids at 100m and 33m.

Grid Extent Outer Grid: 52km x 33km

3D sigma layer model 5-vertical sigma layers with each layer thicknesses 20% of the water column.

Vertical Datum Mean Sea Level (m MSL) which is approximately Australian Height Datum (AHD)

Horizontal eddy diffusivity coefficient 100m Grid = 10 m2/s, 33m Grid = 5 m2/s

Horizontal eddy viscosity coefficient 100m Grid = 10 m2/s, 33m Grid = 5 m2/s

Vertical eddy viscosity / diffusivity k-ε turbulence closure model

Time step (2D model) 0.25 mins (15 secs)

Time step (3D z-layer) 0.25 mins (15 secs)

Bed friction Chezy 65m1/2/s



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Figure 4.2: Local Hydrodynamic Model - Domain Decomposition Grid setup

4.3 Model Setup

4.3.1 Bathymetry

The existing case bathymetry has been compiled from the available data sources around the Darwin project location with all data converted to mean sea level (MSL) according to the Darwin Harbour tidal planes in the numerical model (refer Table 3.1).

The bathymetry and survey data sources are as follows in order of preference (highest to lowest): 1. 1m resolution compiled bathymetric survey collected in 2015; 2. 1m resolution compiled bathymetric survey collected in 2010 and 2011; 3. Australian Hydrographic Chart data (AUS025 and AUS026); 4. 5m resolution DEM compiled from LiDAR data collected over several years.

100m Grid

33m Grid



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The compiled bathymetry grid is shown in Figure 4.3.

Figure 4.3: Bathymetry Grid for Local Scale Model (Datum m MSL Darwin Harbour)

4.3.2 Boundary Conditions

The local model is driven by two offshore water level boundaries with the conditions defined from the regional scale model as shown in Figure 4.4. The north eastern and north western boundaries are water level boundaries with conditions defined from the Regional Model. For the local model, water level is updated every 10 minutes at the boundary.



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Figure 4.4: Local Model Domain ocean side boundary (thick yellow D3D Grid Boundary lines) nested inside Regional Model Domain Flexible Mesh Grid (subset of the entire Regional Model shown in fine orange grid mesh)

4.4 Representative Seasonal Scenarios Modelled

The modelling program for the outfall modelling is based on a scenario modelling approach. The scenario modelling approach has been adopted to optimise the model run times, as continuous modelling of environmental conditions over the full year would be impractical due to the long run times of the model system.

In developing the scenario approach, modelling cases of four weeks duration have been selected that are representative of the dry season and wet season in Darwin. It is noted that the periods selected correspond with times where measured data is available for each location, and therefore where model validation can be completed, as presented and detailed in the next section.

4.4.1 Wet Season

The period selected as representative of the wet season period was 01 January 2016 – 31 January 2016. The month of January 2016 was selected based on the following:



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1. The winds in January from the measured data (3.3.1) represent generally the key wind directions over the wet season months November, December, January and February (Figure 3.7). Analysis of the measured data indicates the wind speed characteristics in the January period selected is generally descriptive of the average of the wet season months.

4.4.2 Dry Season

The period selected as representative of the dry season period was 20 June – 20 July 2019. The period was selected based on the following: 2. The winds from the measured data (3.3.1) represent generally the key wind directions over the Dry

season months May, June July and August (Figure 3.7). Analysis of the measured data indicates the wind speed characteristics are generally descriptive of the average of the dry season months.

3. As measured current and water level data for Elizabeth River is not available for this June/July period, a period of time directly preceding the typical wet season months (April) was selected for validation of dry season conditions at the Elizabeth River location. Analysis of the winds occurring in April 2019 were seen to be generally representative of the winds typically occurring during wet season over the length of the wind record at the Darwin NTC AWS.



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5. Hydrodynamic Model Validation

5.1 Validation of Regional Model

Baird’s regional scale hydrodynamic model has been applied in previous projects in the Northern Territory and comparison of the modelled water levels against the predicted astronomical tide at standard port locations across the northern Australian region shows very good agreement to tidal constants in both amplitude and phase.

A comparison of the modelled water level against predicted water levels (based on tidal constituents) for the full year of 2011 are shown in Figure 5.1. The comparisons for port locations in Darwin Harbour and at nearby port locations in Port Keats (Wadeye), Snake Bay (Milikapiti, Tiwi Islands) and Gove (Nhulunbuy) show excellent agreement.

Figure 5.1: Regional Model Tidal Validation at nearby Port locations

For this project the regional scale model was updated and executed over the 2015 – 2016 and 2018 - 2019 periods to coincide with the metocean data collection campaigns. The regional model uses the TOPEX8 tidal constituents on the boundary with spatial wind and pressure fields from the NCEP Climate Forecast System (CFSR) updated across the model domain hourly throughout the entire model period.



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5.2 Validation of Local Model

5.2.1 Hydrodynamic Model Validation

The validation for the hydrodynamic model has been undertaken, comparing model outcomes with measured data for selected periods where two full spring tides and two full neap tide cycles are completed in the simulations as: 1. a 4-week period in the Dry Season where data was available from the Aquadopp instrument

deployment in the Elizabeth River. The adopted period is 01 April 2019 – 30 April 2019 with model warm-up period of 2 days prior.

2. a 4-week period in the Wet Season where data was available from the Aquadopp instrument deployment in the Elizabeth River. The adopted period is 05 January 2016 –05 February 2016 with model warm-up period of 2 days prior.

3. a 4-week period in the Dry Season where data was available from the Aquadopp instrument deployment in the Darwin Harbour near East Arm. The adopted period is 20 June 2019 –20 July 2019 with model warm-up period of 2 days prior

For the validation of the model, the modelled and measured data is presented as graphical times series in the sections to follow. The detailed statistical analysis of the performance of the model is summarised in Section 5.2.2 thereafter.

The time series plots are presented as follows for the validation: • The comparison of the modelled data against the measured data for the water level, current speed

(depth averaged) and direction is shown in Figure 5.2 for the Elizabeth River location in the Wet Season and in Figure 5.3 for the Dry Season; and

• The comparison of the modelled data against the measured data for the water level, current speed (depth averaged) and direction is shown in Figure 5.4 for the Darwin Harbour East Arm location in the Dry Season. It is noted there is no available wet season data from the Darwin Harbour location with which to make similar comparisons for the wet season.



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Figure 5.2: Comparison of Elizabeth River Location Measured vs Modelled Data for Water level and Depth Averaged Current. Dry Season Validation Period, 1 April 2019 – 30 April 2019.



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Figure 5.3: Comparison of Elizabeth River Location Measured vs Modelled Data for Water level and Depth Averaged Current. Wet Season Validation Period, 5 January 2016 – 5 February 2016.



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Figure 5.4: Comparison of Darwin Harbour Location Measured vs Modelled Data for Water level and Depth Averaged Current. Dry Season Validation Period, 20 June 2019 to 20 July 2019



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5.2.2 Model Metrics -Statistical Descriptions

The model performance has been analysed by comparing the model predictions against the measured data using the statistical descriptions 1. Model skill 2. Bias 3. RMS Error 4. Scatter Index

The derivation of the parameters is outlined in brief in the following sections.

Model Skill

The model skill at simulating the measured conditions is given by Equation 5.1. This produces 0 in cases of no agreement and 1 for perfect agreement between the modelled and measured data.

𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 = 1 − ∑ [𝑀𝑀𝑖𝑖−𝑂𝑂𝑖𝑖]2𝑁𝑁𝑖𝑖=1

∑ ([𝑀𝑀𝑖𝑖−𝑂𝑂�𝑖𝑖]+ [𝑂𝑂𝑖𝑖−𝑂𝑂�𝑖𝑖])2𝑁𝑁𝑖𝑖=1

(5.1)

where:- • Oi observed, or measured data (m/s for wind speed) • Mi modelled data (m/s for wind speed)

Bias

The bias is a measure of the difference between the expected value and the true value of a parameter and is calculated using Equation 5.2. An unbiased model has a zero bias. Otherwise the model is said to be positively or negatively biased, an indication as to whether the model is persistently over or under-predicting the physical conditions, respectively.

𝐵𝐵𝑀𝑀𝐵𝐵𝐵𝐵 = 1𝑁𝑁∑ 𝑀𝑀𝑖𝑖 − 𝑂𝑂𝑖𝑖𝑁𝑁𝑖𝑖=1 (5.2)

RMS Error

The RMS error, Equation 5.3, is also a measure of the difference between the expected value and the true value of a parameter. It provides a measure of the magnitude of the difference between the modelled and measured values.

𝑅𝑅𝑀𝑀𝑀𝑀 = �1𝑁𝑁∑ [𝑀𝑀𝑖𝑖 − 𝑂𝑂𝑖𝑖]2𝑁𝑁𝑖𝑖=1 (5.3)

Scatter index

The scatter index is the RMS error normalised by the mean of the observations – see Equation 5.4. It provides an indication of the scatter of the data about the mean.

𝑀𝑀𝑆𝑆 = �1𝑁𝑁∑ ([𝑀𝑀𝑖𝑖−𝑀𝑀�]−[𝑂𝑂𝑖𝑖−𝑂𝑂�])2𝑁𝑁

𝑖𝑖=1

𝑂𝑂� (5.4)



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5.2.3 Model Validation – Water Levels and Currents

The model metrics have been calculated for the water level, current speed and direction against the measured data in the model cases presented in Figure 5.2 to Figure 5.4,. The metrics are presented in Table 5.1.

Table 5.1: Model Metrics for water level, depth-averaged current velocity and direction

Location Component Skill Bias Scatter RMS Error

Elizabeth River Location DRY SEASON

Water level 1.00 -0.02 0.06 0.23

Current Speed 0.92 0.01 0.42 0.12

U Current 0.96 -0.05 0.12 0.12

V Current 0.92 0.03 0.31 0.08

Elizabeth River Location WET SEASON

Water level 0.99 0.00 0.06 0.25

Current Speed 0.93 0.00 0.37 0.10

U Current 0.97 -0.03 0.10 0.11

V Current 0.97 -0.01 0.15 0.06

Darwin Harbour Location DRY SEASON

Water Level 1.00 -0.01 0.05 0.21

Current Speed 0.94 -0.01 0.29 0.07

U Current 0.98 0.00 0.11 0.07

V Current 0.78 -0.04 0.36 0.09

The validation metrics are very high for all parameters with high model skill and low bias and error metrics. General comments on the Model metrics in Table 5.1 are provided as follows: • The model water level at the Elizabeth River location in both wet and dry season is very closely

matched to the measured data with a model skill value of 1.00 in the dry season case and 0.99 in the wet season case. The modelled water level bias is -0.02m and 0m for the dry season and wet season respectively with very low scatter and RMS error.

• The water level at the Darwin Harbour location has a model skill value of 0.99, with a bias of -0.01m compared to the measured data. The scatter and RMS error values are very low indicating the water level in the model is consistent with the measured data through the time series.

• At the Elizabeth River location, the modelled current magnitude has a model skill of 0.92 and 0.93 in the dry and wet season respectively confirming the model is representing the current magnitude very well. The modelled U directional currents have model skills of 0.96 in both wet and dry season, while the V directional currents have model skills of 0.92 in dry season and 0.97 in wet season. Both U and V directional currents, in both wet and dry season, exhibit very low bias values, confirming the model is representing the current magnitude and direction well at the Elizabeth River Aquadopp location.



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• For the Darwin Harbour location, the model skill at simulating the measured current magnitude is 0.93, with a bias of -0.01ms-1 indicating very good representation of the measured data by the model in this location. The modelled U directional currents have model skills of 0.98 in the dry season, while the V directional currents have a model skill of 0.78. As the most recent bathymetry in the harbour was not available for this project, recent changes to bathymetry may explain the discrepancy in modelled and measured currents in the V direction in this location. Both U and V directional currents exhibit very low bias values, confirming the model is representing the current magnitude and direction well at the Darwin Harbour Aquadopp location.

5.2.4 Spatial Current Fields

Spatial current fields from the local scale model are presented in Figure 5.5 for the flood tide case during a large spring tide. The spatial current field for a large ebb tide map is shown in Figure 5.6. The complex bathymetry and geomorphology of the harbour clearly have a strong influence on both current speeds and directions, and comparison between the flood and ebb tides show stronger currents on the ebb tide (Figure 5.6). While this appears to suggest that outfalls to the harbour could be expected to be carried out of the harbour on the stronger ebb tide currents, further investigation of the period of time the flood and ebb tides cover, and therefore the influence of the flood/ebb tide cycle on the mixing and movement of water and outfall plumes within the harbour. The current speeds at the Darwin Harbour East Arm location are lower than the current speed at the Elizabeth River location in the spatial maps. These modelled outcomes correspond with the analysis of the measured current data and rose plots in the metocean summary in Section 3.2.3.

Figure 5.5: Local Model Grids – Flood Tide for Large Spring Tide Case (06 Apr 2019 1900UTC)

Darwin Harbour Adopp

Elizabeth River Adopp



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Figure 5.6: Local Model Grids – Ebb Tide for Large Spring Tide Case (07 Apr 2019 0030UTC)

5.2.5 2D and 3D Model Comparisons

Preliminary analysis of the 2D and 3D current velocity and direction at the Darwin Harbour location from the model results and the measured data (Aquadopp) to compare the characteristics of the flow through the water column was completed.

The depth averaged current velocity from the 2D model was compared against the 3D sigma-layer model (see Table 4.1) outcomes at the specific model layers at the surface, mid-depth and near bed level. This comparison is shown in Figure 5.7 for a time of spring tides over the 48-hour period 01 – 03 July 2019. The comparison of the 2D depth average and mid-depth current in the 3D simulation shows close agreement. The upper surface current velocity from the 3D simulation is approximately 10% higher than the mid-depth current speed and the bed layer currents show a reduction in velocity of approximately 15% compared with the mid-depth. The application of the 3D model will be important to resolve density driven flows in the outfall modelling.

Darwin Harbour Adopp

Elizabeth River Adopp



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Figure 5.7: Comparison of modelled 2D and 3D current speed timeseries data from the Darwin Harbour East Arm Location

The current velocity from the 3D model at the specific model layers at mid-depth and near bed level were compared against the measured data from the Aquadopp instrument. This comparison is shown in Figure 5.8 for a time of spring tides over the 48-hour period 01 – 03 July 2019. The measured current velocity profile between mid-depth and bottom layer is reasonably well represented in the Delft3D model. and current direction is reasonably reproduced in the model. The comparisons show the direction of the current is reasonably uniform through the water column.

Figure 5.8: Comparison of 3D current speed and direction modelled and measured data from the Darwin Harbour Aquadopp

A further validation description for the modelled to measured depth averaged current is shown in Figure 5.9, with measured to modelled bed level current comparison at the same location and time frame shown in Figure 5.10 and measured to modelled mid-level current comparison in Figure 5.11. Overall, the validation metrics are consistent for all these cases. The 2D model is considered suitable to describing far field flow processes in the wider study area and the depth-averaged assumption is valid for period of validation and calibration data. The 3D model has been validated to well describe the velocity profile near the seabed, and 3D modelling will be applied where required to confirm nearfield mixing, and farfield mixing during potentially stratified conditions.



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Figure 5.9: Comparison of Darwin Harbour Location Measured vs Modelled Data for Water level and Depth Averaged Current



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Figure 5.10: Comparison of Darwin Harbour Location Measured vs Modelled Data for Water level and bottom layer currents



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Figure 5.11: Comparison of Darwin Harbour Location Measured vs Modelled Data for Water level and bottom layer currents



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6. Conclusions The TNG Darwin Processing Facility Outfall Project is a greenfields magnetite concentrate refining project proposed on land adjacent the Elizabeth River Bridge, Middle Arm, Darwin, Northern Territory (NT). Land to the north, south and west contains intertidal areas and mangrove forests that connect the site to the Elizabeth River and Darwin Harbour, and have been zoned for Conservation.

Baird Australia Pty Limited (Baird) has been engaged by Animal Plant Mineral Pty Ltd (APM) to develop a hydrodynamic modelling program to support the environmental approvals process to assess: • Dilution contours around the outfall in typical wet and dry season conditions; • Predicted mixing zones required to meet the level of ecological protection of the waters surrounding

the mixing zone; and. • Provide outputs and reporting in a format suitable to support the development of a Marine


To support the study, metocean measurements have been collected within the Elizabeth River nearby the planned processing facility site, and from a location within Darwin Inner Harbour (upper East Arm region) by O2Marine. From these sites, data has been collected over the period 27 March 2019 to 24 July 2019. At both the Elizabeth River location (27 Mar 2019 to 22 May 2019) and the Darwin Harbour location (22 May 2019 to 24 Jul 2019), an Aquadopp was deployed providing water level current speed and direction.

These data sets have been compiled and a summary of the metocean conditions is presented for the TNG Darwin Processing Facility Outfall project in Section 3. In general: • The current velocity is higher within the Elizabeth River compared to the Darwin Harbour site and ebb

currents are higher than flood tide current velocities. The direction of the Elizabeth River currents is aligned generally a northwest-southeast axis, whilst for the Darwin Harbour site, currents are on a west to north-east plane.

Analysis of the measured climate data from a Bureau of Meteorology site at Darwin NCT AWS to the north west of the site confirms distinct wet and dry season conditions at the location: • The dry season (generally May to October) is characterised by hot temperatures, easterly to south-

easterly winds and clear and stable conditions derived from the subtropical high-pressure ridge. • In the wet season months (generally November to April) the wind climate is more active and

dominated by westerly and north-westerly winds.

The regional and local scale hydrodynamic model system was established for the project: 1. The regional scale model has adopted Baird’s existing Delft-Flow Flexible Mesh (D-Flow FM) model of

northern Australia. The model is driven by tidal constituents along its open boundaries and NCEP CFSR winds and atmospheric pressure across the domain, with bathymetry defined from hydrographic chart data and local scale bathymetry sources where available.

2. The local scale hydrodynamic model is established over the Darwin Harbour area with boundary conditions defined by the Regional model. The local model is setup in a domain decomposition grid arrangement to optimise the efficiency of the model performance, with an outer grid capturing the wider Darwin Harbour area, and inner grid covering the upper East Arm and Elizabeth River area.

The validation for the hydrodynamic model has been undertaken over 4-week periods in the wet season and the dry season from both the Elizabeth River location and Darwin Harbour location where two full spring tide and neap tide cycles are completed through the duration.



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For the validation of the hydrodynamic model, the modelled and measured data is presented as graphical times series in Section 5. Additionally, the model performance was compared against the available measured data using the statistical descriptions of Model skill, Bias, RMS Error and Scatter Index.

The validation metrics calculated for water level, depth averaged current velocity and direction are very high providing a high level of confidence in the application of the model for the outfall plume dispersion. Validation parameters show high model skill and low bias and error metrics as shown in Table 6.1.

Table 6.1: Model Metrics for water level, depth-averaged current velocity and direction

Location Component Skill Bias Scatter RMS Error

Elizabeth River Location DRY SEASON

Water level 1.00 -0.02 0.06 0.23

Current Speed 0.92 0.01 0.42 0.12

U Current 0.96 -0.05 0.12 0.12

V Current 0.92 0.03 0.31 0.08

Elizabeth River Location WET SEASON

Water level 0.99 0.00 0.06 0.24

Current Speed 0.93 0.01 0.37 0.10

U Current 0.97 -0.03 0.10 0.11

V Current 0.97 -0.01 0.15 0.06

Darwin Harbour Location DRY SEASON

Water Level 1.00 -0.01 0.05 0.21

Current Speed 0.94 -0.01 0.29 0.07

U Current 0.98 0.00 0.11 0.07

V Current 0.78 -0.04 0.36 0.09

A comparison of the 2D depth average current velocity against through the water column currents from the 3D simulations (5-layer sigma layer model in Delft3D) was made for the upper layer, mid depth and bed level. The analysis indicates the upper surface current velocity from the 3D simulation is approximately 10% higher than the mid-depth current speed and the bed layer currents show a reduction in velocity of approximately 15% compared with the mid-depth.

Examination of the current direction measured through the water column from the Darwin Harbour location against the simulated 3D through the water column currents (5-layer sigma layer model in Delft3D) shows that the current direction is generally uniform at all depths for the Darwin Harbour location through the tide cycle. The outcome confirms the general flow characteristics of the study area can be described with a depth-averaged 2D model, however the 3D model will be important to resolve density driven flows in the outfall modelling and this will be applied in the immediate vicinity of the proposed outfall locations examined.



13135.101.R1.Rev0 Page 48

In conclusion, the validation of the 2D/3D hydrodynamic model system has confirmed it is accurately reproducing the general hydrodynamic forcing for the overall Darwin Harbour project area. The validation metrics for the Elizabeth River and Harbour locations (Table 6.1) provides confidence the model can be applied in the outfall modelling studies to follow.



13135.101.R1.Rev0 Page 49

7. References

ANZECC & ARMCANZ (2000). Australian and New Zealand Guidelines for Fresh and Marine Water Quality (Australian and New Zealand Environment and Conservation Council (ANZECC) & Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ).

BOM (2016). Climate Classification Maps http://www.bom.gov.au/jsp/ncc/climate_averages/climate-classifications/index.jsp?maptype=tmp_zones#maps Date of access 27 August 2019.

BOM (2019) Climate Statistics for Australian Locations: Summary Statistics for DARWIN AIRPORT http://www.bom.gov.au/climate/averages/tables/cw_014015.shtml Date of access 27 August 2019.

Deltares (2018), Delft3D Model Overview, https://oss.deltares.nl/web/delft3d/about

Inpex (2014). Darwin Harbour – A Summary of the Ichthys LNG Project Nearshore Environmental Monitoring Program. Prepared by Cardno.

http://www.bom.gov.au/jsp/ncc/climate_averages/climate-classifications/index.jsp?maptype=tmp_zones#maps

http://www.bom.gov.au/jsp/ncc/climate_averages/climate-classifications/index.jsp?maptype=tmp_zones#maps

http://www.bom.gov.au/climate/averages/tables/cw_014015.shtml

https://oss.deltares.nl/web/delft3d/about

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