Project Sea Dragon Stage 1 Hatchery Coastal Environment and Impact Assessment

Seafarms Group Limited

October 2017

Document Status

Version Doc type Reviewed by Approved by Date issued v01 Draft Report Christine Arrowsmith Christine Arrowsmith 08/09/2017 V02 Draft Report Christine Arrowsmith Christine Arrowsmith 9/10/2017 V03 FINAL Christine Arrowsmith Christine Arrowsmith 24/10/2017 V04 FINAL Christine Arrowsmith Christine Arrowsmith 26/10/2017

Project Details

Project Name Stage 1 Hatchery Coastal Environment and Impact Assessment Client Seafarms Group Limited Client Project Manager Ivor Gutmanis Water Technology Project Manager Elise Lawry, Joanna Garcia-Webb Water Technology Project Director Christine Lauchlan-Arrowsmith Authors EAL, PXZ, JGW Document Number 3894-26_R01v03_GunnPt_NOI.docx

COPYRIGHT

Water Technology Pty Ltd has produced this document in accordance with instructions from Seafarms Group Limited for their use only. The concepts and information contained in this document are the copyright of Water Technology Pty Ltd. Use or copying of this document in whole or in part without written permission of Water Technology Pty Ltd constitutes an infringement of copyright.

Water Technology Pty Ltd does not warrant this document is definitive nor free from error and does not accept liability for any loss caused, or arising from, reliance upon the information provided herein.

15 Business Park Drive Notting Hill VIC 3168

Telephone (03) 8526 0800 Fax (03) 9558 9365 ACN 093 377 283 ABN 60 093 377 283

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EXECUTIVE SUMMARY Project Sea Dragon is a proposed large scale, integrated, land based prawn aquaculture venture operating across northern Australia. At full production, the proponent, Seafarms Group Limited (Seafarms), intends to provide 100,000 tonnes of prawns to the Australian and Asian markets annually. Water Technology Pty Ltd has been commissioned by Seafarms to undertake an assessment of the existing physical processes, environmental values and water quality of the coastal environment and the impact upon these processes and environment of the proposed Stage 1 Hatchery, to be located at Gunn Point.

The proposed Gunn Point Stage 1 Hatchery is to be located on Murrumujuk Drive between the Tree Point Conservation area and the former Gunn Point Prison Farm, as shown in Figure 1-1. The current proposal includes construction of land based facilities, an intake pipe and pump facility to draw water into the facility and a discharge pipe and flow control to cycle water from the facility back to the open waters of Shoal Bay.

The discharge will be equivalent to the volume of water drawn from the ocean to circulate through the facility. This will be on average 954 kL/day.

The waters around the site comprise of Shoal Bay to the west and Hope Inlet to the south. A number of freshwater waterways flow into Shoal Bay and Hope Inlet, with Howard Springs Creek the most notable waterway. Minor creeks drain across Murrumujuk to the north of the facility. The freshwater waterways are presented in Figure 1-2.

The study involved a desktop literature review, physical data collection and numerical modelling. The existing coastal environment is described in Section 2. The potential impacts of the proposed facility and their control measures are summarised below. A full description can be found in Sections 4 to 6.

Potential Impacts & Mitigation - Coastal Values

The main coastal features at Gunn Point that could be potentially impacted by the proposed facility are in the vicinity of the intake and discharge pipe location.

Both pipes will be buried under the dune and out as far as possible through the intertidal zone via directional drilling. Offshore, once directional drilling is no longer possible, they will be placed on the seabed. There is potential that the pipe could interrupt sediment transport within the intertidal zone. This could lead to a change in the configuration of the intertidal flats as material accumulates on either side of the pipe, and a net loss of material is experienced away from the pipe.

There may be some visual disturbance due to the construction of the pipe, in an area with a low level of development.

The presence of the pipes in this area could impede navigation of recreational vessels in the area.

Control Measures

The following actions are recommended to ensure there is minimal impact of the project on the coastal values

around Gunn Point:  Ensuring adequate scour protection is provided in the design of the pipe bedding

 Minimise the visual impact of the pipe across the intertidal bank by extending the buried section of pipeline as far offshore as possible. 04_GunnPt_NOI  Employ directional drilling as a method of pipeline construction to minimise impacts to vegetation

 Install navigational markers to notify boaters of the potential hazard of the pipeline 26_R01v -

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Potential Impacts & Mitigation – Bathymetry, Sediment Transport & Coastal Processes

Placement of the intake pipe on the bed will result in minor and localised changes to the bathymetry in deeper water due to scour and deposition. More significant changes could be observed in the intertidal region where sediments are more mobile, however this is still expected to be relatively minor.

Discharge flows have the potential to cause scour of the bed, however it is unlikely due to the low flow rate.

Control Measures

The intake and discharge pipes will be buried underneath the dune and across the intertidal zone. To minimise impacts to the coastal processes, these should be buried as far offshore as possible.

Ensure adequate scour protection is provided in the design of the pipe bedding and construction.

Mitigate the potential for scour across the discharge point by ensuring appropriate scour protection is considered during the detailed design phase.

Potential Impacts & Mitigation – Oceanographic Conditions

The macro tidal environment within Shoal Bay means that the potential changes to tidal water levels and currents associated with the intake or discharge are extremely low. The tidal prism (i.e. the volume of water which is exchanged during each tide) in the vicinity of Gunn Point north of Hope Inlet is of the order of 4 x 107 m3 during a spring tide and 4 x 106 m3 during a neap tide. During a single tide, the intake pipe will remove approximately 500 m3 of water from Gunn Point (over approximately 12 hours) at the ultimate development state. This represents 0.001% of the tidal prism during a spring tide and 0.01% during a neap tide and is thus unlikely to have any impact on tidal water levels or currents.

High tidal currents will necessitate the armouring of the intake pipe to the bed to prevent damage through movement. Rock armouring along the pipeline, or concrete braces could be considered.

Control Measures

Removal and discharge of seawater through the intake / discharge pipes is unlikely to result in any changes to the hydrodynamic conditions.

Design of adequate anchoring of the pipes will be required to ensure they are stable.

Potential Impacts & Mitigation – Water Quality

The Water Quality Objectives for Darwin Harbour recommend the water quality that supports the maintenance of the ecosystem, and are designated under Part 7 of the N.T. Water Act as a local guideline level in accordance with the National Water Quality Management Strategy (NWSMS) and Australia and New Zealand Environment and Conservation Council (ANZECC) guidelines (DENR, 2016). The estuary classifications of upper, mid and outer are defined by flushing times (DENR, 2009):

 Upper estuary zones are considered poorly flushed, with residence times over 32 days.

 Mid estuary zones have greater mixing, with residences times between 14 and 32 days.

 Outer estuary areas have considerable mixing with the ocean; residence times are less than 14 days.

Outer Estuary objectives can be applied to areas offshore from Gunn Point and Shoal Bay, and in the outer

04_GunnPt_NOI areas of Hope Inlet. The flushing times at various locations within Hope Inlet were assessed to categorise that area (Section 3.2.1); the assessment revealed that mid-estuary objectives apply further upstream within Hope Inlet. Background concentrations and water quality objectives for upper and mid-estuary are presented in the 26_R01v - table below. 3894

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Parameter Background Concentration (g/L) Darwin Harbour WQO (g/L) Mid Estuary TN 230 270 TP 15 20 Chlorophyll a 2.1 2 (3.4) Outer Estuary TN 160 440 TP 8 20 Chlorophyll a 0.5 1

The above table indicates the background mid-estuary chlorophyll a concentration is above the corresponding water quality objective. When defining performance objectives, in accordance with National Guidelines (ANZECC 2000), there is an accepted hierarchy of documentation in this regard. This hierarchy requires that where there are no locally specific guidelines (which would require comprehensive local water quality data collection typically spanning at least a 1 to 2-year period), management decisions should default to relevant State based guidelines, and in their absence to National guidelines.

In this instance, local monitoring has been undertaken to obtain the background concentrations. Given the Darwin Harbour WQO is assigned to the full harbour system, including Shoal Bay and Hope Inlet, it is proposed that the WQO objective be adjusted at this location for the purposes of this assessment. The upper-estuary Darwin Harbour WQO is 4 g/L, and the mid-estuary WQO 2g/L. Examination of the available water quality data indicates an 80th percentile value of 3.4g/L. Using the 80th percentile as an objective is in line with the recommendations in the National Guidelines. This value sits between the mid and upper WQOs, which appears to be a reasonable interim trigger value to adopt on this basis. Further investigation will be conducted going forward to refine this value. This value is included in the table above in brackets.

The proposed facility will have operating conditions and discharge characteristics similar to the existing Seafarms Hatchery operations at Flying Fish Point, Innisfail in North Queensland. As such, Seafarms propose to adopt the water quality licence conditions for that facility set by the Queensland Department of Environment and Heritage Protection (QLD DEHP). The median licence conditions and concentrations for the key nutrients assessed in the modelling exercise are displayed below.

Licence Discharge Conditions Median (g/L) Total Nitrogen 2000 Total Phosphorous 400 Chlorophyll a 20

In the analysis presented in Section 5.2.5, the background concentration is added to the discharge concentration, and compared to the water quality objective for mid and outer estuary respectively.

The water quality objectives are not predicted to be exceeded by the proposed facility discharge.

04_GunnPt_NOI Cumulative Impacts

The concentration at the two Leanyer Sanderson Wastewater Treatment plant monitoring sites in Shoal Bay 26_R01v - (sites 14 and 15 in the box and whisker plots) indicate any cumulative impacts as a result of the operation of

3894 the proposed facility are predicted to be negligible. As presented in Section 3.4.1, the background

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concentration at these sites are well above the WQO. The predicted change in concentration from the contribution from the proposed facility is at least a factor of 10 below the existing concentration.

Recirculation Impacts

During some meteorological and/or tidal conditions, there will be some minor recirculation of the discharge water to the intake location. The presence of low concentrations of discharge water at the intake poses a potential risk to biosecurity for the proposed facility. Seafarms propose to dose the discharge ponds with hydrogen peroxide to mitigate this risk.

The majority of the recirculation events are due to periods of high rainfall. The corresponding freshwater flow discharging from Hope Inlet constrains the discharge to the north, which results in minor recirculation of the discharge water at the intake site. The few events predicted to occur during the dry season are a result of neap tidal cycles, combined with elevated wind speeds coming from the south-east. This results in reduced mixing, and circulation patterns that increase the concentration at the intake site.

Water Quality Control Measures

The impacts of the discharge have been minimised though selecting a location for the discharge that was optimal in terms of reduction of environmental impacts. The modelling demonstrates that significant impacts as a result of the discharge are not expected to occur. As such no further mitigation is needed, however, as detailed engineering design of the discharge structure itself has not been completed for the project at this time, the opportunity exists to provide further reductions in nutrient concentrations within the receiving environmental system via a discharge diffuser. It is recommended that the discharge process is designed to maximise the dilution as it enters the water column.

Summary of Development Impact on Water Quality

The proposed facility is not predicted to lead to an exceedance of the Water Quality Objectives. Minor recirculation at the intake site will be mitigated by dosing of hydrogen peroxide at times of reduced mixing. This is not an environmental risk, but rather an operational risk in terms of biosecurity.

Potential Impacts & Mitigation – Climate Change

The main components of the coastal environment and the Gunn Point facility that are exposed to the climate change threats are considered to belong to the following three main categories:  Intake and Discharge Infrastructure  Land based facilities

 Water quality and circulation.

Intake and discharge Infrastructure

Threats

The intake and discharge infrastructure are vulnerable to potential changes to the shoreline through increased

inundation or coastal erosion due to increases in mean sea level, storm tides and wave action. Higher wave energy could result with deeper water during storm events which may impact the bed more than present conditions.

Consequences 04_GunnPt_NOI The consequences of changes to the shoreline are likely to be minimal for the intake and discharge pipe

26_R01v locations as the pipe will be buried. Consideration should be given to bury them deep enough so as to not be - exposed during an erosion event. 3894

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Increased wave energy on the bed could lead to increased scour and movement of the pipelines, potentially causing damage to the pipe and loss of production.

Mitigation  Accommodated by designing intake and discharge facilities setback from the present-day coastline to allow for any changes as a result of increased inundation to 2100.  Intake pipe and bedding design should consider the potential for increased wave conditions into the future.

 Where the pipes are buried, they should be deep enough such that they do not become exposed during erosion events.

Land based facilities

Threats  Facilities associated with the project adjacent to or near the existing shoreline could potentially be exposed to threats associated with shoreline recession. The proposed location of the facility is approximately 150m landward of the existing vegetation line. The proposal is at concept stage only and further refinement of the footprint is to be completed.

 The elevation of the development is above the predicted storm tide levels thus the inundation threat is low.

Consequences

Areas of the facility located adjacent to the existing shoreline could potentially be impinged upon by shoreline recession hazards by 2100. The consequences of exposure to this risk include potential exposure to more significant inundation by storm tides, exposure of the buried intake / discharge pipelines, and foundation instability risking building integrity.

Mitigation

The likely extent of erosion by 2100 should be included in the detailed design process, and the facility design adapted accordingly.

Water Quality and Circulation

Threats

As sea levels rise, there will be greater water exchange occurring and a net effect of more flushing, which should see lower concentrations of the discharge waters within the Gunn Point region.

Consequences

There are unlikely to be any adverse consequences.

Mitigation

Not required.

Conclusions

Section 7 presents a risk assessment of the risks posed to the marine physical environment as a result of this 04_GunnPt_NOI proposed project. This addresses the potential impacts and consequences of the construction and operational phases of the project, along with residual risk following implementation of the proposed mitigation measures. 26_R01v

- The risk assessment of the marine physical environment impacts of the project are provided in Table 7-2. This indicates all identified risks as low following implementation of mitigation measures. 3894

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CONTENTS

1 INTRODUCTION 12 1.1 Background 12 1.2 Development Proposal 12 1.3 Study Area 13 1.4 Scope of Works 14 1.5 Assessment Approach 14 1.6 Regulatory Framework 17 1.7 Environmental Objectives and Targets 18

2 EXISTING COASTAL ENVIRONMENT 19 2.1 Existing Values 19 2.2 Regional Climatic Conditions 20 2.3 Oceanographic Conditions 27 2.4 Extreme Conditions 35 2.5 Geomorphology 38 2.6 Sediment Transport and Coastal Processes 45

3 EXISTING WATER QUALITY 48 3.1 Water Quality Drivers 48 3.2 Water Quality Objectives 49 3.3 Monitoring Programs 51 3.4 Nutrients Sources 59

4 POTENTIAL IMPACTS AND MITIGATION – COASTAL ENVRIONMENT 64 4.1 Coastal Values 64 4.2 Bathymetry and Geomorphology 64 4.3 Oceanographic Conditions 65 4.4 Sediment Transport and Coastal Processes 65

5 POTENTIAL IMPACTS AND MITIGATION – WATER QUALITY 66 5.1 Numerical Modelling 66 5.2 Dispersion & Dilution of Discharge 66 5.3 Water Quality Control Measures 79 5.4 Summary of Development Impact on Water Quality 79

6 CLIMATE CHANGE IMPACT ASSESSMENT 80 6.1 Background 80 6.2 Threat Identification 80

04_GunnPt_NOI 6.3 Exposure to Risk 81 26_R01v - 3894

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7 CONCLUSIONS 84

8 REFERENCES 86 Model Domain 89 Model Calibration & Validation 91

APPENDICES Appendix A Description of Numerical Models

LIST OF FIGURES Figure 1-1 Gunn Point Breeding Centre Location and Preliminary Footprint 13 Figure 1-2 Gunn Point Breeding Facility Location 14 Figure 1-3 Numerical model Domain (top); mesh resuolution around discharge location (bottom) Bathymetric values are to AHD 16 Figure 2-1 Location and Proximity of BoM Weather Stations & AIMS buoys to Gunn Point 20 Figure 2-2 Long-term average air temperature, Darwin Airport 21 Figure 2-3 Half hourly measured air temperature at Darwin Airport, Darwin Harbour outer and Beagle Gulf 22 Figure 2-4 Monthly Rainfall (Darwin Airport & Shoal Bay) 23 Figure 2-5 Monthly Evaporation Variation 24 Figure 2-6 Wet and Dry Season Wind Climate (period of Record) 25 Figure 2-7 Darwin Harbour Catchments (left) and Sub-CatChment area (right) (Soure: NRETAS, 2009) 26 Figure 2-8 Long-term Streamflow Data at Howard River (1996-2017) (Source: NT Water Portal) 27 Figure 2-9 Gauged Flow Data for Howard River and Scaled Flows for other catchments 27 Figure 2-10 Predicted tidal and measured water levels 28 Figure 2-11 Measured current data, AIMS buoys Darwin (top) and Beagle Gulf (bottom) 29 Figure 2-12 Modelled Currents Offshore Gunn Point During Spring Peak Ebb (top) and Flood (bottom) Tides 30 Figure 2-13 Shoal Bay WQ results for Temperaure (DENR Report Cards 2013, 2014, 2015) - (box plots show 5th, 10th, 25th, median, 75th, 90th and 95th percentiles) 31 Figure 2-14 Measured water temperature, 2016-17 (top) and long term measured water temperature at Darwin NTS facility (BoM) (bottom) 32 Figure 2-15 Temperature Profiles, November 2016, December 2016, January, February, March and April 2017 33

Figure 2-16 Shoal Bay Wave Conditions (Significant Wave Height), Dry Season (left) and Wet Season (right) 34 Figure 2-17 Shoal Bay Wave Conditions (Wave Period), Dry Season (left) and Wet Season (right) 34 Figure 2-18 Cyclone within 100km of Darwin (1906 – 2017) 36 Figure 2-19 Potential present-day storm tide inundation at Gunn Point (based on GeoScience Australia 04_GunnPt_NOI 5m Topographical Lidar DEM) 38 Figure 2-20 Approximate Location of Shoreline 18,000 and 10,000 years ago (Woodroffe 1986) 39 26_R01v - Figure 2-21 Joseph Bonaparte Gulf (JBG) System (Source: Department of the Environment, Water, Heritage and the Arts, 2007) 39 3894

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Figure 2-22 Diagrammatic cross-section showing the relationship between Cretaceous and Basement Rocks (Doyle, 2001) 41 Figure 2-23 Vegetation Map of Darwin Region (Source: Oosterzee 2014) 42 Figure 2-24 Schematic profile Diagram indicating the typical pattern of zonation of mangroves in Darwin Harbour (MetcaLfe, 2007) 42 Figure 2-25 Bathymetry and Topography 44 Figure 2-26 Bed Sediment Sampling, Shoal Bay (GA, 2016) 45 Figure 2-27 Coastline Change Based on Landsat Imagery 1995 – 2017 47 Figure 3-1 Model Extraction Points 50 Figure 3-2 Shoal Bay WQ results for Nutrients (DENR Report Card 2009-2016) – Median Values are reported. 53 Figure 3-5 Water quality monitoring sites; model extraction points 54 Figure 3-6 Typical Salinity Values for Wet and Dry Seasons (DENR, 2009) 55 Figure 3-7 Shoal Bay Measured Salnities (DENR Report Cards) 56 Figure 3-8 Offshore Salinity variartion (BlueLink, CSIRO) 56 Figure 3-9 Measured Salinity at Darwin Buoy (top), BeaGLE Gulf Buoy (middle) and gunn Point Logger (Bottom) 57 Figure 3-10 Salinity Profiles, November 2016, December 2016, January 2017, February, march and April 2017 58 Figure 3-11 Shoal Bay Turbidity and TSS Results (DENR Report Card 2009-2016) – Median Values are reported 59 Figure 3-12 Pollution sources and ecology for Shoal Bay (DENR 2009) 60 Figure 3-13 Buffalo Creek WQ results for Nutrients (DENR Report Card 2016) - (box plots show 5th, 10th, 25th, median, 75th, 90th and 95th percentiles) 61 Figure 5-1 Modelled discharge and intake points; facility footprint 67 Figure 5-2 Impact assessment sites 70 Figure 5-3 Predicted Mid-Estuary Total Nitrogen concentration at model output sites: 2005/06 (top) 2016/17 (bottom) 72 Figure 5-4 Predicted Mid-Estuary Total Phosphorous concentration at model output sites: 2005/06 (top) 2016/17 (bottom) 73 Figure 5-5 Predicted Mid-Estuary Chlorophyll a concentration at model output sites: 2005/06 (top) 2016/17 (bottom) 73 Figure 5-6 Predicted Outer-Estuary Total Nitrogen concentration at model output sites: 2005/06 (top) 2016/17 (bottom) 74 Figure 5-7 Predicted Outer-Estuary Total Phosphorous concentration at model output sites: 2005/06 (top) 2016/17 (bottom) 74 Figure 5-8 Predicted Outer-Estuary Chloropyhll a concentration at model output sites: 2005/06 (top) 2016/17 (bottom) 75 Figure 5-9 Median predicted Total Nitrogen concentration for 2005-2006 simulation (left); 2016-2017 simulation (right) 76

Figure 5-10 Median predicted Total Phosphorous concentration for 2005-2006 simulation left); 2016- 2017 simulation (right) 76 Figure 5-11 Median predicted Chlorophyll a concentration for 2005-2006 simulation left); 2016-2017 simulation (right) 77 Figure 5-12 Tracer concentration at the intake site 2005-2006 simulation and corresponding rainfall rate 04_GunnPt_NOI (top); 2016-2017 (bottom) 78 Figure 8-1 Model Domain (top) and mesh resolution around discharge (bottom). Bathymetric values are 26_R01v

- to AHD 90 3894

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Figure 8-2 Water level calibration: Astronomical tides at Nightcliff (top), Measured water levels at AIMS Beagle Gulf A and Outer Darwin (middle) and Gunn Point (lower) 91 Figure 8-3 Measured versus modelled salinity 92 Figure 8-4 Water Technology predicted currents (top) AIMS currents (bottom) for Flood Tide 93 Figure 8-5 Water Technology predicted currents (top) AIMS currents (bottom) for Ebb Tide 94 Figure 8-6 Astronomical tidal currents offshore of the discharge over one month (top), current speed- direction roses for one month (bottom left), spring tides (bottom centre) and neap tides (bottom right) 95 Figure 8-7 Wind Conditions, January 2006 and long term wet season average 96 Figure 8-8 Wind Conditions, June 2005 and long-term average dry season 97

LIST OF TABLES Table 1-1 Objectives and Performance Criteria – Marine and Estuarine Waters 18 Table 2-1 Nightcliff Tidal Planes (ANTT, 2016) 28 Table 2-2 Gunn Point Storm Tide Height (m AHD) 37 Table 2-3 Bed Sediment Samples, Shoal Bay (GA, 2016) 46 Table 3-1 The average Water Quality of the main body of Darwin Harbour and Shoal Bay (Source: DENR, 2009) 48 Table 3-2 Darwin Harbour Water Quality Objectives (DENR 2016) 49 Table 3-3 Flushing Times withn Hope Inlet (blue shaded sites are mid-esuary) 51 Table 3-4 Median Background nutrient concentrations 54 Table 3-5 Pollutant loads into Darwin Habour in a typical wet season rainfall (1.67m), 2006/07 (Source: NRETAS, 2009) 62 Table 3-6 Predicted Increase in Diffuse Pollutant Loads from all projected Developments for the Entire Darwin Harbour Region (Source: NRETAS, 2009) 63 Table 3-7 Ambient Fresh Water Quality, Howard River (DENR 2009) 63 Table 5-1 Licence discharge conditions 67 Table 5-2 Median Background nutrient concentrations 69 Table 5-3 Mid Estuary Assessment Sites 71 Table 5-4 Outer Estuary Assessment Sites 71 Table 6-1 IPCC 2014 Projected Sea Level Rise 80 Table 6-2 Predicted Storm Tide Levels (m AHD) 81 Table 7-1 Risk Assessment Matrix 84 Table 7-2 Gunn Point Risk Assessment 85

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1 INTRODUCTION 1.1 Background Project Sea Dragon is a proposed large scale, integrated, land based prawn aquaculture venture operating across northern Australia. At full production, the proponent, Seafarms Group Limited (Seafarms), intends to provide 100,000 tonnes of prawns to the Australian and Asian markets annually.

Water Technology Pty Ltd has been commissioned by Seafarms to undertake an assessment of the existing physical processes, environmental values and water quality of the coastal environment and the impact upon these processes and environment of the proposed Stage 1 Hatchery to be located at Gunn Point.

1.2 Development Proposal The proposed Stage 1 Hatchery is to be located to the south of Murrumujuk Drive between the Tree Point Conservation area and the former Gunn Point Prison Farm, as shown in Figure 1-1.

The proposal includes construction of land based facilities, an intake pipe and pump facility to draw water into the facility and a discharge pipe and flow control to cycle water from the facility back to the open waters of Shoal Bay.

The discharge will be equivalent to the volume of water drawn from the ocean to circulate through the facility. This will be on average 954 kL/day. The layout of the facility is presented in Figure 1-1.

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FIGURE 1-1 GUNN POINT BREEDING CENTRE LOCATION AND PRELIMINARY FOOTPRINT 1.3 Study Area The Stage 1 Hatchery, referred to in this report as the facility, is to be located in the locality of Murrumujuk, on the eastern shoreline of Shoal Bay. The facility will be accessed via Murrumujuk Drive and Gunn Point Road, approximately 70km drive from Darwin city area.

The Murrumujuk rural area is located on lands to the north of the Shoal Bay Coastal Reserve and Tree Point Conservation Area, and to the south of Gunn and Glyde Points. The waters around the site comprise of Shoal Bay to the west and Hope Inlet to the south.

A number of freshwater waterways flow into Shoal Bay and Hope Inlet from the south, with Howard Springs Creek the most notable waterway. Minor creeks drain across Murrumujuk to the north of the facility whilst to the south, freshwater flows are directed to Shoal Bay via the Hope Inlet. The freshwater waterways are presented in Figure 1-2.

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FIGURE 1-2 GUNN POINT BREEDING FACILITY LOCATION 1.4 Scope of Works The scope of work of this study has been designed to provide sufficient detail to inform a Notice of Intent (NOI) for the development to the Northern Territory Environment Protection Authority (NT EPA). The scope of works has been developed based on earlier studies for Project Sea Dragon for breeding facilities located at Point Ceylon within Bynoe Harbour.

The scope of work is also based on Terms of Reference (ToR) for an Environmental Impact Study (EIS) provided by the NT EPA for the Project Sea Dragon Legune Grow-out facility.

1.5 Assessment Approach

The work required to provide a thorough understanding and description of the existing physical coastal environment at and around the facility has been undertaken as follows:

Desktop Literature Review An extensive literature review was conducted to document the existing coastal environment within Shoal Bay and Hope Inlet. The site is relatively isolated and un-developed and thus previous detailed studies are limited, 04_GunnPt_NOI however where available, data associated with the following have been reviewed:  Geology and geomorphology of Shoal Bay and the Gunn Point peninsula, 26_R01v -  Estuarine and marine water quality including salinity, turbidity and nutrients, 3894

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 Physical oceanography including hydrodynamics, storm surge and waves.

Physical Data Collection

A physical data collection program was undertaken for this study which included the deployment of water level, and salinity data loggers. It also included the collection of bathymetric level data and sediment and water quality samples to assist in characterising the physical coastal environment. The data collected was used to support the development and calibration of numerical models of the study area.

Numerical Modelling A suite of numerical models including hydrodynamic and transport models were developed to enable the simulation of the tides, wastewater discharges, and freshwater inflows on physical processes within the Study Area. MIKE by DHI Modelling suite was used to assess the conditions and impacts of the development within the study area.

The MIKE models utilise a “flexible mesh” (FM) system which allows areas of interest to be resolved at a higher detail and in a combination of triangles and rectangular elements. Model mesh resolution at the discharge and intake point is in the order of 100m and 60m respectively. Offshore the element size is up to 1,000 ha. The model domain and mesh resolution is presented in Figure 1-3. Refer to Appendix A for details on the numerical modelling.

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04_GunnPt_NOI FIGURE 1-3 NUMERICAL MODEL DOMAIN (TOP); MESH RESUOLUTION AROUND DISCHARGE LOCATION (BOTTOM) BATHYMETRIC VALUES ARE TO AHD 26_R01v -

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1.6 Regulatory Framework Legislation, guidelines, and state planning policies relevant to the management and protection of the coastal environment at the facility include, but are not limited to:  Australian and New Zealand Guidelines for Fresh and Marine Water Quality 2000;

 Environment Protection and Biodiversity Conservation Act 1999;  Territory Parks and Wildlife Conservation Act  Waste Management and Pollution Control Act

 Northern Territory Water Act

 Dangerous Goods Act

 Fisheries Act  Marine Act  Water Act

The regulatory requirements of relevance to this report are discussed below:

Northern Territory Environmental Protection Authority Guidelines (NT) The NT EPA has developed a series of draft and current guidelines related to the Environmental Assessment Act and Waste Management and Pollution Control Act. These guidelines are policy documents that describe the minimum expectations of the NT EPA in relation to a particular matter. Potentially relevant guidelines include:

 Guidelines on Conceptual Site Models  Guidelines on Mixing Zones

Australian and New Zealand Guidelines for Fresh and Marine Water Quality 2000 (National)

Often referred to as the Australian Water Quality Guidelines (AWQG), or the ANZECC Guidelines, these are part of the National Water Quality Management Strategy (NWQMS). The aim of the guidelines is to 'provide an authoritative guide for setting water quality objectives required to sustain current or likely future environmental values for natural and semi-natural water resources in Australia and New Zealand'. To this end, the AWQG provide guidance on setting and selecting appropriate water quality objectives, based on a hierarchy starting at:  Local Guidelines, then

 State Guidelines, then  National (AWQG) guidelines.

In essence, this hierarchy requires that where there are no locally specific guidelines (which would require comprehensive local water quality data collection typically spanning at least a 1 to 2-year period) that management decisions should default to relevant State based guidelines, and in their absence to National guidelines. 04_GunnPt_NOI 26_R01v - 3894

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1.7 Environmental Objectives and Targets The overarching objective of hydrodynamic and receiving water quality assessments relating to the project is to ensure that surface waters, including estuarine and marine waters, are protected both now and in the future, such that the ecological health, and the health, welfare and amenity of people are maintained.

In this regard, the key values to be protected in relation to estuarine and marine waters are:  Marine and estuarine aquatic ecosystems  Human consumers (primarily for fish species)

 Cultural and spiritual values of marine and estuarine waters, including ecosystems and biota

 Suitable salt water supply to support the Project (primary industries, aquaculture), primarily related to the intake waters.

Key environmental protection objectives and their related specific criteria to protect these environmental values are outlined in Table 1-1.

TABLE 1-1 OBJECTIVES AND PERFORMANCE CRITERIA – MARINE AND ESTUARINE WATERS

Objectives Targets Protection of marine and estuarine Construction works operate under ESCP and ASSMP, with: aquatic ecosystems  No significant erosion or sediment loss from the site due to site construction activities

 No oxidation of acid sulfate soils on the site due to site activities  No leaks or spills Operations:  WQOs for slightly – moderately disturbed marine and estuarine ecosystems1

Maintenance of the cultural and WQOs as specified above. spiritual values of marine and estuarine waters, including ecosystems and biota Ensure a sustainable and suitable No changes in the tidal water level or salinity regime in Shoal Bay salt water supply to support the that would affect its key role in supplying suitable quality salt water Project to the project Appropriate engineering design at Engineering design by registered professional engineer, following the intake and settlement ponds to advice of registered geotechnical engineer ensure long term stability and integrity of structures and supply

Table notes:

1 refer to Section 3 and Section 5.2.3

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2 EXISTING COASTAL ENVIRONMENT 2.1 Existing Values Environmental Values (EVs) are referred to the qualities of waterways that help support aquatic ecosystems and human uses. Aquatic ecosystem EVs are divided into categories reflecting the degree of modification from a natural status.

2.1.1 Environmental Values

Shoal Bay

Shoal Bay is listed as a Site of International Significance by the Northern Territory Government for the following reasons (Aurecon 2013):

 Extensive tidal flats providing important feeding and roosting area for migratory shorebirds  Small inland freshwater wetlands frequented by up to 5,000 waterbirds  Patches of rainforest around the margin of the tidal flats

 Threatened species including three plants, ten vertebrates and one invertebrate

The Darwin Harbour region, including Shoal Bay in the vicinity of the intake and discharge licence area for the Project, is subject to a Beneficial Use Declaration under the Water Act (The Northern Territory Government Gazette No. G27, 7 July 2010). This lists the following beneficial uses as applying to marine and estuarine waters in this area:  Aquaculture  Environment

 Cultural

Tree Point Conservation Area

Tree Point Conservation Area is located approximately 35 km northeast from Darwin City and is situated just to the northwest of Shoal Bay Coastal Reserve and south of Murrumujuk Drive, protecting a coastal strip of Shoal Bay on the Tree Point Peninsula. The conservation area is fringed by coastal vine thicket and a swampy flood plain which is home to a large mangrove habitat and wetland birds such as Brolgas and Black-necked Stork. A tidal creek runs through the conservation area and towards the Shoal Bay Costal Reserve (NT government 2016).

Shoal Bay Coastal Reserve Shoal Bay Coastal Reserve is situated approximately 35 km northeast of Darwin and protects a large area of

eucalypt woodland and saline wetlands. It is a habitat for saltwater crocodiles. The coastal reserve has a total area of 121 km2 and protects a large area between Howard River and Tree Point Conservation area.

The Coastal reserve is also a culturally significant site for the Larrakia people, the indigenous group traditionally owning the coastal area around Darwin. 04_GunnPt_NOI 2.1.2 Cultural Values 26_R01v - There are more than 200 archaeological sites in the greater Gunn Peninsula region which are significant in the cultural evolution of the Aboriginal coastal communities in the region (Calnan 2006). 3894

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Hope Inlet, located at the southern point of Shoal Bay, has a high density of archaeological sites where three Aboriginal shell mounds are located. These mounds provide evidence of late Holocene economies on the Beagle Gulf mainland.

Murrumujuk, in the western side of the Gunn Peninsula, is of significant cultural value. Seven registered sacred sites are located at the Murrumujuk beach.

2.2 Regional Climatic Conditions The climate at Gunn Point Peninsula is tropical monsoonal in nature with a hot and dry season during the southern hemisphere’s winter months of June to August and a hot and humid wet season during the summer months of December through February; transitional conditions occur between these two periods. The wet season is characterised by warm air temperatures, convective storms and monsoonal weather accompanied by heavy rain and strong north-westerly winds, as well as cyclonic weather in some years. During the dry season, cooler air temperatures, south-easterly winds and little or no rain define the typical weather pattern.

A description of the climatic variation across the seasons and typical and extreme values is provided below. Data has been sourced from the Bureau of Meteorology (BoM) at a number of stations around Gunn Point. Additionally, weather data has been sourced from Australian Institute of Marine Science (AIMS). These stations and their proximity to Gunn Point are shown below in Figure 2-1. A reasonable length of records exists for the stations.

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FIGURE 2-1 LOCATION AND PROXIMITY OF BOM WEATHER STATIONS & AIMS BUOYS TO GUNN POINT 26_R01v - 3894

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2.2.1 Air Temperature

The closest meteorological station to Gunn Point with a full record of data maintained by BoM is located at Darwin Airport. Figure 2-2 below shows the monthly minimum, maximum and mean air temperature variation for 33 years at the BoM weather station at Darwin Airport. There is only minor variation compared with the average temperature across the Darwin region.

Variation in daily minimum and maximum temperatures across the year can be seen, with the greatest average daily temperature range of 15oC to 33oC in June and July. The lowest daily variation occurs during January and February where the average daily minimum and maximum temperature ranges between 28oC and 34oC.

The hottest months are the transitional months of September to December where the average daily maximum temperature is close to 35oC.

FIGURE 2-2 LONG-TERM AVERAGE AIR TEMPERATURE, DARWIN AIRPORT

Air temperature at the Darwin Airport station, the AIMS Darwin NRS buoy and the AIMS Beagle Gulf buoy are presented in Figure 2-3. The figure illustrates the more variable cooling and heating effect of land at the Darwin airport station compared with ocean air temperatures at the AIMS buoys. The thermal mass of the ocean is much slower to heat and cool than the land, and as such the daily variation at the AIMS buoys is around 5°C whilst the change on land can exceed 10°C over a 24-hour period.

Air temperature around Darwin peaks during November and December before falling through January and the end of the wet season, to the cooler dry season months of June and July. An intense low system can be observed in the April data with temperatures dropping below 20°C overnight with the storm front.

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FIGURE 2-3 HALF HOURLY MEASURED AIR TEMPERATURE AT DARWIN AIRPORT, DARWIN HARBOUR OUTER AND BEAGLE GULF

2.2.2 Rainfall

Rainfall has been recorded for varying time periods for the stations presented above in Figure 2-1. The average monthly rainfall recorded at Shoal Bay and Darwin Airport stations are displayed in Figure 2-4. The figure illustrates that rainfall across the region is fairly consistent when considering monthly and annual averages. Review of individual station data suggests that geographically isolated storms occur during the wet season and high rainfall may only be recorded at a single gauge; however, this evens out across the month and season. The mean monthly rainfall at the sites are presented in Figure 2-4, along with the cumulative total average monthly rainfall (at Darwin Airport) through the year. At Darwin Airport, the average annual rainfall is close to 1,700mm with the majority occurring in the wet season.

The rainfall patterns are consistent between the relatively sparse locations, indicating that whilst tropical storms during the wet season can be quite isolated in space and time, the daily rainfall across the wider area is largely consistent.

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FIGURE 2-4 MONTHLY RAINFALL (DARWIN AIRPORT & SHOAL BAY)

2.2.3 Evaporation

The high temperatures and high humidity lead to high rates of evaporation in the region. This evaporation can impact shallow or still water bodies and cause increases in salinity in some coastal estuaries.

Evaporation is measured by the BoM at the Darwin Airport on a daily basis. A summary of the daily average evaporation between 1977 and 2017 is provided below in Figure 2-5. As shown, average daily evaporation increases through the dry season before peaking in October, at or prior to the onset of the wet season and then reducing through the wet season to March.

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FIGURE 2-5 MONTHLY EVAPORATION VARIATION

2.2.4 Wind Conditions

The monsoonal climate around Gunn Point results in a reversal of the general wind patterns through the year. Wind roses for the wet season months of December through February, and the dry season months June through August are shown below in Figure 2-6 for a number of locations around Gunn Point. As illustrated, during the wet season, winds are generally from the west through northwest. During the dry season, winds are predominantly from the east and southeast.

Further analysis of the wind climate indicates that during the wet season, winds shift from westerly in the morning to north-westerly in the afternoon. During the dry season, conditions are more variable with winds early in the dry season shifting from east and south-easterly in the morning to east in the afternoon and from east and southeast in the morning to north and north-westerly in the afternoon during August.

Wind speeds are relatively low, the 6-minute average wind speeds are predominantly below 10m/s. Gust speeds, the highest 3 second duration wind recorded during a 30-minute period, can however exceed 28m/s (over 100km/h) during large storm events. Cyclonic winds and their frequency of occurrence are discussed in Section 2.4.

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(a) Darwin Airport (b) Darwin NTC (c) Charles Point

FIGURE 2-6 WET AND DRY SEASON WIND CLIMATE (PERIOD OF RECORD) 26_R01v04_GunnPt_NOI - 3894

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2.2.5 Freshwater Inflows

Darwin Harbour catchment covers an area of 2,010 km2. Gunn Point is located within Howard River sub- catchment with an approximate catchment size of 542 km2 (NRETAS, 2009). Darwin Harbour sub-catchments and their non-urban, urban and total catchment area are presented in Figure 2-7.

FIGURE 2-7 DARWIN HARBOUR CATCHMENTS (LEFT) AND SUB-CATCHMENT AREA (RIGHT) (SOURE: NRETAS, 2009)

Gauged streamflow data is available for Howard River continuously since 1996 (Figure 2-8), however, catchments which drain into Hope Inlet and along the north coast of Darwin are ungauged. Therefore, to illustrate stream flows for smaller creeks near Gunn Point, flows have been scaled from Howard River gauging station based on the catchment size and are presented for November 2016 to April 2017 in Figure 2-9. These scaled flows are estimates only. The figure also illustrates the short lived and peaky nature of runoff in the waterways. Location of these smaller creeks are shown in Figure 1-2 in Section 1.3.

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FIGURE 2-8 LONG-TERM STREAMFLOW DATA AT HOWARD RIVER (1996-2017) (SOURCE: NT WATER PORTAL)

FIGURE 2-9 GAUGED FLOW DATA FOR HOWARD RIVER AND SCALED FLOWS FOR OTHER CATCHMENTS

Pollutant loads from each catchment is detailed in Section 3.4.2. 2.3 Oceanographic Conditions

2.3.1 Tides

Water level variations at Gunn Point are primarily driven by astronomical tidal forces which result in a spring tide range of close to 8 m. Smaller variation in water levels are caused by atmospheric conditions such as storm surges and regional setup and set downs due to the movement of water from the Gulf of Carpentaria, and more distantly the Pacific Ocean and the impacts of the Southern Oscillation/El-Nino effect.

Measured water levels offshore from Gunn Point, Darwin Harbour and within the Beagle Gulf are presented in

26_R01v04_GunnPt_NOI Figure 2-10, along with predicted tides at Nightcliff, the NTC tidal station located between Darwin and Shoal - Bay (location shown on Figure 2-1). Tidal planes at Nightcliff are presented in Table 2-1. 3894

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The consistency of the tidal pattern and range across the southern shoreline of the Beagle Gulf, along Darwin and into the shoreline at Gunn Point is noted. The maximum measured water level during the 2016-17 wet season at Gunn Point is in the order of 3.7-3.8m AHD, indicating some residual setup at the logger. The gauge has not been corrected to the Australian Height Datum (AHD) and is an estimate only based on mean sea level during the deployment. Conditions at the time of the peak water level included sustained and strong westerly and north-westerly winds. Measured data at the AIMS buoy offshore also indicated the maximum water level offshore in the order of 3.6m AHD, however during a different period.

The minimum water level measured at Gunn Point was in the order of -4.0m AHD for the 2016-17 wet season. Again, the level to AHD has been estimated based on mean sea level for the deployment. The minimum low water occurred in conjunction with large tidal ranges in the Northern Territory so is representative of more extreme (a few times per year) conditions.

TABLE 2-1 NIGHTCLIFF TIDAL PLANES (ANTT, 2016)

Tidal plane HAT MHWS MHWN MLWN MLWS LAT (m AHD) Nightcliff 3.6 2.8 1.0 -0.9 -2.6 -3.9

FIGURE 2-10 PREDICTED TIDAL AND MEASURED WATER LEVELS

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2.3.2 Currents

Measured current data is available from the AIMS buoys within Beagle Gulf. No measured current data is available in the vicinity of the site at Gunn Point.

Currents measured during the 2016-17 wet season are presented in Figure 2-11. Currents at both locations are highly directional, with currents close to the Darwin Harbour entrance running northwest to southeast, whilst those further offshore in the Beagle Gulf are largely east-west. Current speeds peak towards the surface, with currents during spring tides above 1.0m/s at both sites.

FIGURE 2-11 MEASURED CURRENT DATA, AIMS BUOYS DARWIN (TOP) AND BEAGLE GULF (BOTTOM)

The Australian Institute of Marine Science (AIMS) has developed a hydrodynamic model of Darwin Harbour which has been undergoing refinements and updates since 2006 as new field data is collected (Williams, 2006). Water Technology has used the results of this calibrated, validated model to validate our hydrodynamic modelling, in terms of modelled currents, offshore from Gunn Point. AIMS current maps for ebb and flood currents during a spring tide are presented in Figure 2-12. These give an indication of the circulatory patterns in the area.

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FIGURE 2-12 MODELLED CURRENTS OFFSHORE GUNN POINT DURING SPRING PEAK EBB (TOP) AND FLOOD (BOTTOM) TIDES

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2.3.3 Water Temperature

Water temperatures in Darwin Harbour exhibit seasonal variation as well as the daily fluctuation due to solar radiation. Typically, lowest temperatures occur during the dry season (23°C) in June and July and highest temperatures occur during the wet season months in October and November (33°C) (NTEPA, 2012).

Temperature at a few locations in Shoal Bay has been monitored by DENR. Box plots were published in the 2013, 2014 and 2015 Report Cards. Typically, these box plots are based on data collected during the monitoring campaign and seasonal variation is not indicated (Figure 2-13). A temperature range of 23°C to 33°C is reported here between 2013 and 2015.

FIGURE 2-13 SHOAL BAY WQ RESULTS FOR TEMPERAURE (DENR REPORT CARDS 2013, 2014, 2015) - (BOX PLOTS SHOW 5TH, 10TH, 25TH, MEDIAN, 75TH, 90TH AND 95TH PERCENTILES)

Water temperature data has been collected across the 2016-17 wet season by the AIMS buoys, loggers deployed at Gunn Point for the purpose of this investigation, and the Bureau of Metrology (BoM) as part of the Australian Baseline Sea Level Monitoring Program (ABSLMP). This data is presented in Figure 2-14.

During this time, water temperature around Darwin peaks during the wet season with the long-term average (based on measured data in Darwin Harbour), building to above 31° C during November and December before dropping through January to around 28.5° C in May.

Water temperatures around Darwin through the 2016-17 wet season are generally lower offshore and at the bed, however are relatively consistent in patterns of increase and decrease across the 8 months of data. Daily variation of temperature is higher on the surface, as would be expected. Daily rainfall is also shown in the

figure and illustrates the impacts of strong monsoonal fronts on the water temperature due to rainfall and lower air temperature. A cold front in early April results in a notable drop in water temperature, particularly closer to shore at the Gunn Point and Darwin Harbour stations. 26_R01v04_GunnPt_NOI - 3894

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FIGURE 2-14 MEASURED WATER TEMPERATURE, 2016-17 (TOP) AND LONG TERM MEASURED WATER TEMPERATURE AT DARWIN NTS FACILITY (BOM) (BOTTOM)

Depth Profiles

Depth profiles have also been collected at a number of locations around Gunn Point during mid-November 2016, mid-December 2016, mid-January 2017, mid to late February 2017, late March 2017 and mid-April 2017 (Figure 2-15). For the November measurements, temperatures at the surface are consistently higher by approximately 0.5°C than the bed layer (32.3°C). Conditions during December and January represent a more well-mixed water column. In February, surface temperatures are approximately higher by 0.5°C in the surface layer at the time of the sampling. Temperatures show a decreasing trend in March and April as the dry season begins. Well-mixed conditions in April reach a low of 29°C.

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November December January 2016 2016 2017

March 2017

February April 2017 2017

FIGURE 2-15 TEMPERATURE PROFILES, NOVEMBER 2016, DECEMBER 2016, JANUARY, FEBRUARY, MARCH AND APRIL 2017 26_R01v04_GunnPt_NOI -

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2.3.4 Waves

Offshore wave conditions have been extracted from the National Ocean Atmospheric Administration (NOAA) Wave Watch III (WW3) model to provide an understanding of the offshore wave climate which may impact Shoal Bay and the proposed facility. NOAA provides a global model reanalysis hindcast of 3-hourly data for the period 1979 through to 2016. The model time step means that short duration events such as cyclones are not well resolved. Extreme wave conditions associated with tropical cyclones are therefore not considered in this analysis. Extreme wave conditions at Gunn Point associated with tropical cyclones are discussed further in Section 2.4.1.

Wave conditions from the global model during the wet and dry season offshore from Gunn Point within the Beagle Gulf are shown in Figure 2-16 and Figure 2-17. The following features of the wave climate can be observed:

 Offshore wave conditions mimic the seasonal reversal of the dominant wind direction shown in Figure 2-6.

 Dry season conditions are very calm with a large proportion of the record indicating wave heights less than 0.4m.  Wet season conditions are more energetic, with close to 50% of the period experiencing wave heights greater than 0.5m. Waves are predominantly from the west, with a small proportion of waves from the west-northwest.

Due to the exposure of the shoreline opposite Murrumujuk to Beagle Gulf, wave conditions are expected to be in line with the offshore wave conditions.

The fetch at Gunn Point extends approximately 9000 kilometres away from the coast across the Indian Ocean, and therefore large swells are expected along the shoreline both during wet and dry season. Swell waves are generated by storms thousands of kilometres away and therefore do not follow local wind patterns.

FIGURE 2-16 SHOAL BAY WAVE CONDITIONS (SIGNIFICANT WAVE HEIGHT), DRY SEASON (LEFT) AND WET SEASON (RIGHT)

FIGURE 2-17 SHOAL BAY WAVE CONDITIONS (WAVE PERIOD), DRY SEASON (LEFT) AND WET SEASON 26_R01v04_GunnPt_NOI - (RIGHT) 3894

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2.4 Extreme Conditions 2.4.1 Tropical Cyclones

Tropical cyclones occur on average once per year in the area of the Northern Territory west of the Gulf of Carpentaria (around 2 per year occur within the Gulf) (BoM, 2017). Cyclones which may affect the region will typically form in the Timor Sea to the west, or the Arafura Sea to the north during the months of November through to April. Cyclones forming in these areas typically travel in a southwest and west direction, travelling parallel with the general shape of the coastline.

Statistics provided by the BoM show that 104 cyclones were recorded in the Northern Territory and the Gulf of Carpentaria (including Queensland) in the period between 1960 and 2007. Of these, 31 were considered “severe” – a category 3, 4 or 5, and 4 were category 5 events. Detailed review of BoM data indicates that 37 cyclones have been recorded within a 100km radius of the proposed facility since 1906. 10 cyclones passed within 50km of Gunn Point (see Figure 2-17).

Statistics developed by the BoM indicate that a cyclone could be expected to occur within the area around Gunn Point once every 2 – 3 years. However, wider climatic weather patterns have an impact on cyclone frequency, with more cyclones occurring during La Niña cycles when the frequency could be expected to be closer to 2 every 3 years (BoM, 2017).

The main structural features of a tropical cyclone are the eye, the eye wall and the spiral rainbands. The four main components of a tropical cyclone that combine to make up the total cyclone hazard are described below:  Extreme Winds – Maximum wind speeds are a function of the central pressure, the radius to maximum winds, the forward speed of the cyclone and local topographic effects. Cyclonic winds circulate clockwise in the Southern Hemisphere; however, the wind fields are generally asymmetric such that the strongest winds are generally observed on the left-hand side of the direction of the cyclone movement. During a coastal crossing at Shoal Bay, the cyclonic wind direction will be onshore north of the eye and offshore south of the eye.

 Extreme Waves – Tropical cyclones can generate very large ocean waves as a result of the transfer of energy from the wind to the ocean surface. The growth of ocean waves is a function of the fetch (the distance the wind acts over), wind speed, wind duration, the depth of water and the size of the cyclone. The area to the north of Shoal Bay is protected from very long fetch waves by Bathurst and Melville Islands. Wave fetch and water depth increase to the northwest and west and therefore extreme wave conditions are likely to propagate into Shoal Bay from these directions.  Storm Surge –Tropical cyclones can produce significant storm surges near the coastline. Storm surges are meteorologically forced increases in coastal water levels caused by the combined action of extreme surface winds (which drive ocean currents towards the coastline) and the reduction in atmospheric pressure (which causes a local rise in sea level). The peak of a tropical cyclone storm surge generally only lasts for a few hours near the region of maximum wind speeds.  Intense Rainfall – The rain bands of a tropical cyclone can expand up to 1000 km in diameter with the

heaviest rainfall usually located within the eye wall. Rainfall is not directly correlated to cyclone intensity and recent low category cyclones have resulted in near record rainfalls within the Darwin region (BoM, 2017). 26_R01v04_GunnPt_NOI - 3894

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FIGURE 2-18 CYCLONE WITHIN 100KM OF DARWIN (1906 – 2017)

2.4.2 Storm Tides

Predicted Storm Tides The term storm tide refers to coastal water levels produced by the combination of astronomical and meteorological sea-level forcing. The meteorological component of a storm tide is commonly referred to as storm surge and collectively describes the variation in coastal water levels in response to atmospheric pressure fluctuations and wind setup.

Storm tide modelling was completed for the Gunn Point and Darwin area by Systems Engineering Australia Pty Ltd (SEA, 2010). The study provided a prediction of existing storm tide levels for a number of return periods. Storm tide levels for Gunn Point and Darwin City are provided in Table 2-2. Around Gunn Point, the resolution of the SEA modelling was 0.005 degrees (approximately 560m).

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TABLE 2-2 GUNN POINT STORM TIDE LEVEL (M AHD)

Return Period (Average Recurrence Interval, ARI) 50 100 500 1,000 10,000 Gunn Point 2010 3.3 3.4 3.6 3.7 4.4 2050 3.6 3.7 4 4.2 4.9 2100 4.0 4.1 4.5 4.8 6.1 Darwin City 2010 4.5 4.7 5.1 5.3 5.8 2050 4.9 5.1 5.5 5.7 7.2 2100 5.4 5.6 6.1 6.5 7.6

Recent Cyclones

Cyclone Carlos, a Category 2 storm which occurred in February 2011, resulted in a storm surge level of 0.9 m above the predicted astronomical tide at the Darwin gauge. The storm surge occurred during the end of a neap tide cycle and storm tide levels were not significant. However, had Cyclone Carlos coincided with the peak spring tide 4 days later, the storm tide could have been of the order of 4.5 m AHD – equivalent to a 1 in 50- year event at Darwin (Table 2-2). The eye of Cyclone Carlos remained close to, or south of, the coastline as it travelled westward, resulting in northerly winds occurring after the eye of the cyclone had passed, which then forced water levels high along the coast.

In comparison, Cyclone Ingrid passed over the Tiwi Islands in March 2005 as a Category 3/4 storm with maximum winds in excess of 50m/s. The northerly track of the cyclone resulted in offshore winds at Darwin and a (negative) surge of -0.7m below the predicted tidal level was recorded.

The BoM maintains a tidal station at Darwin as part of the Australian Baseline Sea Level Monitoring Program (ABSLMP). The highest recorded water level at Darwin since 1990 is 4.146m AHD, a level which was reached during the passage of Category 1 Tropical Cyclone Fletcher which passed well south of Darwin. The water level was the combination of a high spring tide, low atmospheric pressure and localised wind squalls.

Storm Tide Inundation The “National 5 metre (bare earth) DEM” sourced from GeoScience Australia (2015) provides a digital surface elevation (DEM) of the site at Murrumujuk. The National 5m DEM is a collection of individual LiDAR surveys undertaken between 2001 and 2015. The LiDAR data has been captured to standards “generally consistent” with specifications to meet a vertical accuracy of 0.3m (95% confidence) and horizontal accuracy of 0.8m (95% confidence). The present-day storm tide levels presented in Table 2-2 have been overlain on the DEM and are shown in Figure 2-19.

Along the shoreline at Murrumujuk, the large tidal range provides a buffer against the impacts of the more irregular cyclone events and associated storm tide. Elevated non-extreme storm tidal levels which have the potential to cause inundation may be experienced frequently. For instance, the Highest Astronomical Tide (HAT) of 3.6m AHD described in Section 2.3.1 is defined as occurring (without the influence of any meteorological impact) once every tidal epoch (18.6 years). However, due to the low likelihood of a storm event and the HAT coinciding, the HAT level is above the 50-year storm tide return period. The MHWN (1m AHD) and the MHWS (2.8m AHD) are shown on the figure to illustrate the more frequently inundated areas. 26_R01v04_GunnPt_NOI - 3894

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The figure illustrates that under existing conditions, infrastructure on the site is not likely to be inundated. There is some overland flow to the south of the proposed facility through Tree Point and Little Tree Creeks, but this is unlikely to reach the development.

FIGURE 2-19 POTENTIAL PRESENT-DAY STORM TIDE INUNDATION AT GUNN POINT (BASED ON GEOSCIENCE AUSTRALIA 5M TOPOGRAPHICAL LIDAR DEM) 2.5 Geomorphology The geomorphology of the study area can be examined at a range of scales, including the regional context of the Joseph Bonaparte Gulf, Beagle Gulf, the more local context of Darwin Harbour and Shoal Bay, to the tide dominated Hope Inlet area and tidal creeks such as the Howard River. Each component has its own characteristics which are linked via their physical conditions, hydrology, sediment transport and water quality dynamics. This section broadly describes the geomorphic characterisation of the study area at these different scales.

2.5.1 Joseph Bonaparte Gulf

Northern parts of Australia and New Guinea were connected nearly 11,000 years ago (during the late Pleistocene-early Holocene from 18,000-9,000 years BP), when the continental shelf (Sahul Shelf) was exposed above sea level (Figure 2-20). During extended periods of exposure to subaerial erosion, the seabed topography of this area was eventually formed. From around 9,000 years BP, with the rise of sea levels this area transitioned to a fully-open marine system. During the Late Quaternary, the environment of the Bonaparte Depression (a 150m deep depression in Joseph Bonaparte Gulf (Figure 2-21)) varied with fluctuating sea 26_R01v04_GunnPt_NOI - levels and climatic conditions, from an estuarine embayment to a shallow, freshwater lake. Bonaparte 3894

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Depression is a muddy, depositional basin that accumulates organic detritus and mud settling out of the water column (Department of the Environment, Water, Heritage and the Arts, 2007).

FIGURE 2-20 APPROXIMATE LOCATION OF SHORELINE 18,000 AND 10,000 YEARS AGO (WOODROFFE 1986)

FIGURE 2-21 JOSEPH BONAPARTE GULF (JBG) SYSTEM (SOURCE: DEPARTMENT OF THE ENVIRONMENT,

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Upwelling There are no major ocean currents in Joseph Bonaparte Gulf. Tidal currents here are the most significant force in the movement of sediments and biota, particularly in the inshore areas and around islands and reefs. The local upwellings around the reefs are also mainly the result of these strong tidal currents. The Indonesian Throughflow brings low salinity warm water from the Pacific Ocean through the Timor Trough which in turn drives upwellings of cold water onto Sahul shelf. Upwelling generally occurs between July and August (Department of Environment, Water, Heritage and the Arts, 2007).

2.5.2 Beagle Gulf

The Beagle Gulf is located at the eastern edge of the Bonaparte Depression which forms as a large, shallow embayment between the Tiwi Islands north of Darwin and the Kimberley ranges in north-eastern W.A. The Bonaparte Basin drains through the former Pleistocene coastline splitting the outer bank of the Sahul Shelf with an incised channel between 150 – 200m deep. A secondary flow path from the Beagle Gulf drains to the east of Van Diemen Rise and represents the ancient flow paths from the Beagle Gulf.

Van Deimen Gulf is located to the east of the Beagle Gulf, connected by Clarence Strait and the Vernon Islands.

The Beagle Gulf is dominated by tidal currents which amplify as they transit across Sahul Shelf, and the currents become more bidirectional as they approach the coast (Siwabessy, 2015).

Within Beagle Gulf, the predominant underlying rock layers are the Permian siltstones and sandstones of Bonaparte Gulf Basin in the west. In the east, Proterozoic siltstones and sandstones of the Pine Creek Geosyncline constitute the dominant lithology. Cretaceous sandstones and siltstones of the Bathurst Island formation overlay the areas to the north-east. One of the major geomorphological features are the Vernon Island reef complex to the east and sandy beaches backed by chenier ridge systems and low-cliffed headlands on the western boundary. The proposed Beagle Gulf marine park falls within Anson-Beagle bioregion which is approximately 25 km in width from the highwater mark to the 30 m depth contour offshore (Smith, 2000).

2.5.3 Gunn Point Peninsula

Geomorphology Gunn Point Peninsula is a low-lying coastal plain. Coastal chenier dune systems along the coastline at Gunn Point are significant geomorphologic features of this area. These dunes are formed parallel to the shoreline and are made of deposited materials overlying estuarine mud. They are often the result of catastrophic storms which smash shells and throw them into mounds to form a beach. In front of these beaches, the mangrove belt is formed and advances seawards (Oosterzee, 2014).

Another feature of significance in Gunn Point Peninsula are the intertidal flats and saltmarshes that are found at the base of Shoal Bay, and the rocky reefs on the ocean floor, offshore from the Peninsula (Calnan, 2006).

The coastal plains here consist of saline mud and clay plains. A highly weathered and redeposited geomorphic

unit consisting of gravels, sands, silts and clays dominates the Gunn Point Peninsula. These features which are called Koolpinyah Surface, were deposited during the Tertiary period and have undergone intense weathering to produce a lateritic mantle that contains ironstone and high aluminium levels. The geological cross-section between Darwin City and Mary River is presented in Figure 2-22. 26_R01v04_GunnPt_NOI - 3894

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FIGURE 2-22 DIAGRAMMATIC CROSS-SECTION SHOWING THE RELATIONSHIP BETWEEN CRETACEOUS AND BASEMENT ROCKS (DOYLE, 2001)

Vegetation

Gunn Point Peninsula has a rich vegetation including areas of rainforest, savannah woodlands, wetlands, mangroves, salt flats, tidal habitats and coral reefs as shown in Figure 2-23.

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FIGURE 2-23 VEGETATION MAP OF DARWIN REGION (SOURCE: OOSTERZEE 2014)

Metcalfe studied the four main mangrove assemblages of Darwin Harbour, namely Hinterland margin, tidal flat, tidal creek and seaward as shown in Figure 2-24. Mangrove communities of Shoal and Gunn Point Peninsula are expected to have similar structural features to that of Darwin Harbour, although the species may not be as diverse. The species are often arranged parallel to the coast. The combined effect of high evaporation rates during the dry season, and soil moisture and salinity as a result of tidal inundation have a strong influence on mangrove vegetation structure and composition in the mid and upper intertidal zone. Further inland, mangroves are generally influenced by freshwater inflows and seasonal deposition of terrestrial sediments (Metcalfe, 2007).

FIGURE 2-24 SCHEMATIC PROFILE DIAGRAM INDICATING THE TYPICAL PATTERN OF ZONATION OF 26_R01v04_GunnPt_NOI - MANGROVES IN DARWIN HARBOUR (METCALFE, 2007) 3894

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2.5.4 Shoal Bay

Geomorphology

The morphology of Shoal Bay is the product of marine transgressions, fluvial erosion and deposition. The present-day estuary was formed as sea levels rose at the end of the last glacial period. During the last glacial period, which ended approximately 12,000 years ago, mean sea levels were approximately 50 metres lower than the present day and the coastline was located off the edge of the continental shelf. During this period, the Beagle Gulf and much of the Timor Sea were gently sloping coastal landforms, connecting today’s shoreline to the Tiwi Islands (Harris et al, 2003).

2.5.5 Murrumujuk

Murrumujuk is a coastal strip located between Gunn Point to the north and Tree Point Conservation area in the south. The locality is characterised by dunes, sandy beaches and grassland with sections of closed forests. A series of unstable cliffs lie behind the main beach in Murrumujuk (Calnan 2006).

Bathymetry

A hydrographic survey of offshore areas at Murrumujuk was undertaken in March 2017. The survey consisted of single-beam soundings running 3-4km perpendicular to the shoreline at distances of 200m to 500m. This localised survey has been combined with the NT Government Outer Darwin Harbour Bathymetric Survey and GeoScience Australia 5m Topographical Lidar DEM and is presented in Figure 2-25.

The proposed facility is located on the high ground to the north of Tree Point. A cross section across the site is shown in Figure 2-25. Cross sections located north and south of the proposed facility illustrate the consistent nature of the offshore bathymetry. The depth alongshore increases relatively rapidly between mean high water springs (MHWS) and mean low water neap (MLWN) at a slope of 1:50 before tapering and reducing slowly offshore below mean low water spring tides at a slope of over 1:700.

For reference, the Mean Low Water Spring (MLWS) at Nightcliff is -3.8m AHD (ANTT, 2016). The -4.0m contour at the proposed facility is located 800-900m offshore from the vegetation line at Gunn Point, which begins at an elevation of greater than 4.5m AHD, around 1.0m above the HAT (+3.6m AHD) at Nightcliff. A coastal dune can be clearly seen in the cross-section profiles below. Landward of the dune, the topography drops to below HAT levels and may be subject to ponding after storm tides or inland flooding. To the north of the site the topography rises rapidly to over 20m AHD, whilst the steep rise in land at the site tapers off above 7m AHD.

Within the Tree Point Conservation Area to the south of the facility, the barrier dune prevents direct inundation from the coast to the tidal inlets to the east where the topography indicates the elevation is around the MHWS level of 2.8m AHD. Tidal inlets are unsurveyed in the Hope Inlet; however, review of satellite and historic aerial imagery indicates the inlets remain inundated and thus it is assumed that a minimum bed level of -4.0m is present within the main waterways.

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Zoomed area below

26_R01v04_GunnPt_NOI - FIGURE 2-25 BATHYMETRY AND TOPOGRAPHY 3894

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2.6 Sediment Transport and Coastal Processes Coastal processes and sediment transport are dominated by the macro tidal regime around Gunn Point. GeoScience Australia conducted a marine survey in outer Darwin Harbour region in 2015 to collect baseline information with an aim to improve the environmental management of Darwin Harbour (GA 2016). As part of this survey, sediment samples were collected at a number of locations in Shoal Bay, offshore from Murrumujuk locality (Figure 2-26). Visual inspection and laboratory analysis indicate a high proportion of muddy material in bed samples within Shoal Bay. The location of these samples and the corresponding sediment properties including % sand, % mud and % gravel as well as the mean sediment size in microns are presented in Table 2- 3.

FIGURE 2-26 BED SEDIMENT SAMPLING, SHOAL BAY (GA, 2016)

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TABLE 2-3 BED SEDIMENT SAMPLES, SHOAL BAY (GA, 2016)

Sampling Longitude Latitude Sediment Description Station (degrees) (Degrees) 1 130.947641 -12.26474 Mud with fine sands, some shells, very few pebbles 54% Mud (M), 42% Sand (S), 3.5% Gravel (G) Mean grain size = 120.8µm 2 130.982516 -12.239960 Mud with fine sand and some shell grit 50% Mud (M), 45% Sand (S), 5.3% Gravel (G) Mean grain size = 243.7µm 3 130.965996 -12.253727 Sand with shell grit, some mud, small flat pieces of yellow clay 8% Mud (M), 72% Sand (S), 20% Gravel (G) Mean grain size = 730.4µm 4 130.967832 -12.231701 Mud with fine sand and shell grit 45% Mud (M), 51% Sand (S), 4.5% Gravel (G) Mean grain size = 247.9µm 5 130.984351 -12.220687 Mud with fine sand 77% Mud (M), 21% Sand (S), 1.7% Gravel (G) Mean grain size = 230.8µm 6 130.952230 -12.275753 Predominantly mud, a few pieces of shell 66% Mud (M), 32% Sand (S), 1.8% Gravel (G) Mean grain size = 103.8µm

Analysis of LandSat (USGS) imagery of the site indicates that the coastline offshore from the Murrumujuk locality has experienced little change in the recent past. Imagery from 1996 and 2017 is shown below in Figure 2-27 where the position of the shoreline in 1996 is shown in red on both images. Negligible coastline change can be detected from these images.

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FIGURE 2-27 COASTLINE CHANGE BASED ON LANDSAT IMAGERY 1995 – 2017

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