HAPTER 17 – OASTAL PRO ESSES€¦ · Chapter 17 – Coastal Processes Page 17-1 17. COASTAL...

CHAPTER 17 – COASTAL PROCESSES

GULF ALUMINA LTD – SKARDON RIVER BAUXITE PROJECT

Skardon River Bauxite Project Chapter 17 – Coastal Processes

Page 17-i

TABLE OF CONTENTS

17.1 Introduction ..................................................................................................... 17-1 17.2 Environmental Objectives and Performance Outcomes ..................................... 17-1 17.2.1 Environmental Objectives ........................................................................................ 17-1 17.2.2 Performance Outcomes ........................................................................................... 17-1 17.3 Legislative and Policy Context ........................................................................... 17-2 17.4 Coastal Processes and the Physical Marine Environment ................................... 17-2 17.4.1 Climate ..................................................................................................................... 17-2 17.4.2 Regional Setting........................................................................................................ 17-2 17.4.3 Skardon River Estuary .............................................................................................. 17-2 17.4.4 Tides ......................................................................................................................... 17-2 17.4.5 Storm Tide ................................................................................................................ 17-3 17.4.6 Tidal Currents ........................................................................................................... 17-3 17.4.7 Waves ....................................................................................................................... 17-4 17.4.8 River Flows ............................................................................................................... 17-4 17.4.9 Bathymetry and Morphology ................................................................................... 17-5 17.4.10 Shoreline and Bank Evolution .................................................................................. 17-9 17.4.11 Marine Water Quality ............................................................................................ 17-10 17.4.11.1 Water Quality Sampling ......................................................................................... 17-10 17.4.11.2 Turbidity ................................................................................................................. 17-12 17.4.11.3 Salinity .................................................................................................................... 17-12 17.4.11.4 pH ........................................................................................................................... 17-12 17.4.11.5 Dissolved Oxygen ................................................................................................... 17-12 17.4.11.6 Nutrients ................................................................................................................ 17-13 17.4.11.7 Metals ..................................................................................................................... 17-13 17.4.11.8 Chlorophyll-a .......................................................................................................... 17-13 17.4.11.9 Hydrocarbons ......................................................................................................... 17-13 17.4.11.10 Summary ................................................................................................................ 17-13 17.4.12 Water Quality Objectives ....................................................................................... 17-14 17.4.13 Sediment ................................................................................................................ 17-16 17.4.13.1 Sediment Sampling ................................................................................................. 17-16 17.4.13.2 Particle Size Distribution ........................................................................................ 17-16 17.4.13.3 Metals ..................................................................................................................... 17-17 17.4.13.4 Nutrients ................................................................................................................ 17-17 17.4.14 Acid Sulphate Soils ................................................................................................. 17-17 17.5 Potential Impacts ........................................................................................... 17-18 17.5.1 Port Construction ................................................................................................... 17-18 17.5.2 Bed Levelling .......................................................................................................... 17-18 17.5.3 Offshore Transhipment .......................................................................................... 17-19 17.5.4 Bulk Vessels ............................................................................................................ 17-19 17.5.5 Hydrodynamics ....................................................................................................... 17-19 17.5.6 Sediment Transport ................................................................................................ 17-19 17.5.7 Shoreline and Bank Evolution ................................................................................ 17-20 17.5.8 Morphology ............................................................................................................ 17-20 17.5.9 Water Quality ......................................................................................................... 17-20 17.5.10 Sediment ................................................................................................................ 17-21 17.5.11 Acid Sulphate Soils ................................................................................................. 17-21 17.6 Mitigation Measures ...................................................................................... 17-22 17.6.1 Vessel Wakes .......................................................................................................... 17-22


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17.6.2 Bed Levelling .......................................................................................................... 17-22 17.6.3 Barge Operations ................................................................................................... 17-22 17.6.4 Prop Wash .............................................................................................................. 17-23 17.6.5 Bauxite Loading ...................................................................................................... 17-23 17.6.6 Water Quality ......................................................................................................... 17-23 17.6.7 Sediment Quality .................................................................................................... 17-25 17.6.8 Acid Sulphate Soils ................................................................................................. 17-26 17.7 Risk Assessment ............................................................................................. 17-26 17.8 Cumulative Impacts ........................................................................................ 17-27 17.8.1.1 Skardon River ......................................................................................................... 17-27 17.8.1.2 Offshore Transhipment .......................................................................................... 17-28 17.8.1.3 Bulk Carriers ........................................................................................................... 17-28 17.9 Conclusion ..................................................................................................... 17-28

Tables

Table 17-1 Tidal Planes ............................................................................................................... 17-3 Table 17-2 Distance with Elevations above -2.2mLAT in the Bed Levelling Areas ..................... 17-6 Table 17-3 Marine Water Quality Sampling ............................................................................. 17-10 Table 17-4 Preliminary Water Quality Objectives .................................................................... 17-14 Table 17-5 Sediment Sampling ................................................................................................. 17-16 Table 17-6 Marine Water Quality Monitoring ......................................................................... 17-24 Table 17-7 Risk Assessment and Management Measures for Impacts to Coastal

Processes and the Physical Marine Environment .................................................. 17-26

Figures

Figure 17-1 Bed Features and Bathymetry of the Skardon River ................................................ 17-4 Figure 17-2 Bed Levelling Areas .................................................................................................. 17-5 Figure 17-3 Bathymetry from 2009, Long-section (Black Line), Chainage (km) and

Proposed Bed Levelling Areas (Red Boxes) .............................................................. 17-7 Figure 17-4 Sea Bed Elevation (m LAT) for Long-section of the Skardon River ........................... 17-8 Figure 17-5 Aerial Photograph of Skardon River from 1989 ....................................................... 17-9 Figure 17-6 Marine Water Quality and Sediment Sampling Locations ..................................... 17-11 Figure 17-7 Particle Size Distribution ........................................................................................ 17-17


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17. COASTAL PROCESSES

17.1 Introduction

This chapter describes the coastal process and physical environment in the Skardon River and coastal areas potentially impacted by the Project, including climate, hydrodynamics, bathymetry, morphology, shoreline evolution, marine water quality and marine sediments. This chapter identifies potential Project impacts on coastal process and the physical environment describes measures to mitigate and manage impacts, and provides a risk assessment for residual impacts. The assessment of the marine environment focusses on the Skardon River, bed levelling area (on the ocean side of the headlands at the mouth of the Skardon River) and offshore transhipment area.

Information in this chapter is primarily based on the information provided in Appendix 8.

Chapter 16 describes the freshwater aquatic environment and ecology of the Project area.

17.2 Environmental Objectives and Performance Outcomes

The environmental objectives and performance outcomes below are based on Schedule 5, Table 2 of the Environmental Protection Regulations 2008 (EP Regulation). The mitigation and management measures presented in this chapter are designed to achieve these environmental objectives and performance outcomes. The environmental management plan (EM Plan) presented in Appendix 13 provides a consolidated description of these mitigation and management measures.

17.2.1 Environmental Objectives

The activity will be operated in a way that protects environmental values of marine waters.

The activity is operated in a way that protects the environmental values of marine sediments.

The location of activities in the marine environment protects environmental values of adjacent

sensitive uses.

The choice of the site, at which the activity is to be carried out, minimises serious environmental harm

on areas of high conservation value and special significance in the marine environment.

17.2.2 Performance Outcomes

Storage and handling of potential contaminants will minimise release to the marine environment.

Contingency measures will prevent or minimise adverse effects on marine water quality or sediment

quality due to unplanned releases of contaminants to the marine environment.

Any discharge to marine waters will be managed so that there will be no adverse effects due to the

altering of existing flow regimes for marine waters.

Activities that disturb marine sediments will be managed in a way that prevents or minimises adverse

effects on environmental values.

Activities in the marine environment are carried out in a way that prevents or minimises adverse

effects on the use of surrounding waters and allows for effective management of the environmental

impacts of the activity.

Shipping activities will be managed to minimise bank erosion potential and habitat impact.

Prevent or minimise the release of ship-sourced pollutants.


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Implement emergency response plans for any hydrocarbon contaminant release.

The disturbance of any acid sulphate soil, or potential acid sulphate soil, will be managed to prevent

or minimise adverse effects on environmental values.

17.3 Legislative and Policy Context

The legislative and policy context for approvals for activities in marine environment is described in Chapter 2.

17.4 Coastal Processes and the Physical Marine Environment

17.4.1 Climate

Climatic factors affecting coastal processes and the physical marine environment are described in Chapter 9 and include rainfall, cyclones, wind speed and wind direction.

17.4.2 Regional Setting

The Gulf of Carpentaria is a large and relatively shallow body of water which is enclosed on three sides by the Australian mainland and bounded on the north by the Arafura Sea. It is 480 km wide and 640 km long with an area of approximately 310,000 km2 and a maximum water depth of 70m. The tidal wave enters from the north-west (the Arafura Sea) and propagates clockwise around its amphidromic point (a nodal point about which the tide rotates). The eastern shoreline current is parallel to the coast at the peak flood and ebb stages of the tide. Tidal signals around the Gulf of Carpentaria are semi-diurnal in the north, decreasing rapidly towards a diurnal signal in the south. At Skardon River the tide signals are mixed but mainly diurnal.

The Gulf of Carpentaria can be subject to seasonal fluctuations in sea level (up to 0.5m) as a result of trade winds (e.g. during the monsoon) and forcing from the Arafura Sea. These seasonal sea level fluctuations can result in large areas only being inundated by tides in the summer months (during the monsoon), as a result these areas cannot support mangrove or freshwater vegetation and therefore form salt flats. In addition, circulation within the Gulf can also be set up due to the wind stress applied by tropical cyclones at the water surface driving wind induced currents and residual water level circulations.

17.4.3 Skardon River Estuary

The Skardon River is classified as a tidal creek as it has a low freshwater input with low-gradient, seaward-sloping coastal flats. These systems are primarily influenced by tidal currents and as a result they comprise of straight, sinuous or dendritic tidal channels that taper and shoal to landward. The mudflats which surround the creeks tend to be high relative to the tidal planes, with seawater being mainly confined to the tidal channels except during high tide on spring tides. Due to the strong tidal currents which occur in tidal creeks as generated by the generally large tidal ranges, they are usually highly turbid.

17.4.4 Tides

The closest standard port to Skardon River with accurate tidal predictions and tidal plane information is Weipa. However, tidal plane information is also available at Cullen Point (near Mapoon) and Vrilya Point (60 km north of the Skardon River) but these are based on less data than for Weipa and are not considered as accurate. In addition, eight months of measured water level data at the Skardon River Barge Ramp has been used to predict approximate tidal planes. The tidal plane information for the four locations is shown in Table 17-1.


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Table 17-1 Tidal Planes

Tidal Plane Weipa

LAT (m)

Cullen Point

LAT (m)

Vrilya Point

LAT (m)

Skardon River Barge Ramp

LAT (m)

HAT (Highest Astronomical Tide) 3.4

MHHW (Mean High High-Water) 2.9 3.0 3.6 3.6

MLHW (Mean Low High-Water) 2.2 2.0 2.4 2.6

MSL (Mean Sea Level)# 1.8 1.8 2.1 2.2

MHLW (Mean High Low-Water) 1.5 1.5 1.9 1.9

MLLW (Mean Low Low-Water) 0.7 0.5 0.6 0.7

LAT (Lowest Astronomical Tide) 0.0 0.0 0.0 0.0

# At Weipa AHD = 1.75 m above LAT which is approximately equal to MSL

The tidal signal at Skardon River is predominantly diurnal with a small semi-diurnal signal which results in a consistent small second high and low water each day. The eight month overview of the tidal signal highlights the variability in the tidal signal, with significant differences between successive lunar cycles (29.5 day cycle). In addition, it also highlights the variability in the semi-diurnal signal over time.

17.4.5 Storm Tide

There is limited storm surge data available for the Skardon River. A detailed storm tide assessment has been carried out at Weipa by Worley Parsons (2008) which can be used to provide an indication of likely storm tide conditions for the Skardon River. The assessment found that the potential for a high storm tide (combined tide and surge) to occur at Weipa was reasonably low, with a 100 year ARI of approximately 2 m above Australian height datum (AHD) (compared to a highest astronomical tide (HAT) level of 1.63 m AHD). The reasons for the predicted relatively low storm tide level was mainly a result of less intense cyclones tending to occur in the area and the likelihood that a rare severe cyclone crosses at the same time as a spring high tide is very low. Based on this analysis and combined with high water levels for the Skardon River expected to be similar as at Weipa, the storm tide levels for the Skardon River are expected to be comparable to Weipa and therefore storm tides are not considered to present a significant risk in the area.

The infrastructure, other than the wharf, within the Port infrastructure area is situated at least above 3 m AHD, and mining will occur on the bauxite plateau above the Port elevation. These areas are considered sufficiently high that sea level rise or storm tide inundation over the 10 year Project life will not present a significant risk.

17.4.6 Tidal Currents

Skardon River is categorised as a tidal creek where tidal currents are the dominant processes, with strong tidal currents expected. It is therefore tidal action which results in the transport of sediment into the estuary, where the sheltered conditions eventually allow the coarser sediment fractions to settle out of suspension. Tidal creeks are usually highly turbid due to the strong tidal currents generated by the macro-tidal ranges allowing fine sediments to remain in suspension during spring tides.

Figure 17-1 shows the bathymetry of the main channel in Skardon River along with areas with different bed forms. Offshore of the entrance mega ripples and sand waves occur in the main channel where current speeds remain high due to the constrained channel focusing the flow, and where the ebb tidal delta forms the tidal currents are much lower as wave action will start to dominate this area. These


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offshore features indicate active coastal processes and the natural sand transport of sand across the entrance to the river.

Figure 17-1 Bed Features and Bathymetry of the Skardon River

17.4.7 Waves

Appendix 8 presents seasonal wave roses. Waves are generated by the dominant east-south-east winds during the dry season, resulting in calm conditions along the east coast of the Gulf. The largest waves which occur are from the west to west-north-west occur during the wet season (summer and part of autumn). The area offshore of the constricted entrance to the Skardon River will be influenced by both offshore generated swell waves and locally generated wind waves. Due to the narrow entrance of the Skardon River (approximately 300m) combined with the complex and relatively shallow bathymetry of the ebb tidal delta and the offshore channel, swell waves are not expected to propagate inside the Skardon River. Due to the configuration of the Skardon River locally generated wind waves in the estuary are not considered to be a significant process.

17.4.8 River Flows

A hydrological assessment, using hydrological modelling, of the Skardon River was undertaken by SRK Consulting Pty Ltd (2013). Based on this assessment the features associated with the Skardon River are as follows:

approximately 30 km long

total catchment area of approximately 480 km2

the catchment has suffered little disturbance

the freshwater discharge is highly seasonal with significantly higher flows in the wet season

(December to April)


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the mean annual discharge is 730,000ML.

The Skardon River is dominated by tidal processes and freshwater flows are relatively low.

17.4.9 Bathymetry and Morphology

Bed levelling is proposed in two areas in the ebb tidal delta area which, for the purpose of this assessment, are referred to as bed levelling area 1 and 2, as shown in Figure 17-2. Bed levelling is proposed at -2.2 m LAT.

Figure 17-2 Bed Levelling Areas

Five hydrographic surveys of the Skardon River were available from 1998, 2002, 2007, 2009 and 2015. All of the surveys extend at least from the ebb tidal delta offshore of the entrance (i.e. inclusive of the bed levelling area) up to the Port location. The change in bed elevation between the hydrographic surveys was reviewed to develop an understanding of the river morphology and its changes.

The distance where sea floor elevations are higher than -2.2 m LAT in the bed levelling areas is shown in Table 17-2, for each of the bathymetrical surveys. Table 17-2 shows how the lowering in elevation in these areas since 1998 has resulted in a reduction in the total channel length requiring bed levelling to a level of -2.2 m LAT by more than 100 m from 1,886 m in 1998 to 1,757 m in 2015.

Over the 17 year period of the hydrographic surveys, the peak elevations in Area 1 have generally reduced in elevation and the width of the area above the bed levelling elevation has also reduced. Accordingly, there has been reduction in the volume of sand above the bed levelling elevation in Area 1. In contrast, although the peak elevations in Area 2 have generally been reducing, the width of the area above the bed levelling elevation has increased. Once width of the bed levelling area is considered, the volume of material requiring bed levelling has remained relatively stable.


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Table 17-2 Distance with Elevations above -2.2mLAT in the Bed Levelling Areas

Bed Levelling Area

Nov 1998 Aug 2002 Aug 2007 Sep 2009 Apr 2015

Area 1 1,454m 1,440m 1,397m 1,238m 1,267m

Area 2 432m 259m 346m 346m 490m

Total 1,886m 1699m 1,742m 1,584m 1,757m

The bed elevation along the approximate deepest section of the channel is shown in Figure 17-3 for a long-section of the Skardon River from the ebb tidal delta to the Port location. The long section with elevation in metres below lowest astronomical tide (m LAT) for each of the hydrographic surveys is shown in Figure 17-4. This shows that the bathymetry in the area between the entrance, including the entrance, and the Port has been relatively stable from 1998 to 2015 (with some small changes close to the entrance between 1998 and 2002). Conversely, the channel bathymetry offshore of the entrance has been more dynamic.

Figure 17-4 shows that between 1998 and 2015 the peak elevation for the two bed levelling areas has reduced from approximately -0.5 m LAT to -1.25 m LAT. The lowest elevations occurred in 2009, and the features have migrated in an offshore direction.

Over the 17 year period only a single tropical cyclone tracked close to Skardon River and this was a Category 1 (the lowest of the five categories) system. Strong winds and large waves during a tropical cyclone have the potential to result in significant sediment transport along the shoreline adjacent to the Skardon River mouth. Accordingly, this could result in significant bathymetric changes to the area offshore of the Skardon River mouth including the channel. As such, the bathymetric changes over the 17 years of data should be considered to represent relatively calm conditions.

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17.4.10 Shoreline and Bank Evolution

Historical aerial photography from 1989 (Figure 17-5) has been compared with recent aerial photography to determine changes to the Skardon River mouth, banks and adjacent shoreline over the last 26 years. The photographs show that there has been little change in the mouth or banks of the Skardon River over this period, indicating that the river has been stable. The adjacent shoreline also has not changed significantly over this period. The configuration of the channel offshore of the Skardon River mouth has also not changed significantly over this period.

The existing configuration of the shoreline to the north and south of the mouth of the Skardon River shows a depositional trend, with the shoreline showing signs of prograding and beach ridges being present. This shows that the orientation, location and width of the channel and adjacent shoals offshore of the river mouth, the river mouth and the adjacent shoreline have been stable over this period.

Sediment which is transported along the shoreline to the mouth of the Skardon River will be transported into the complex configuration of sand shoals and the ebb tidal delta and eventually bypass the river mouth. These shoals and the delta act as stores of sediment which allow sediment transported by longshore drift to bypass the river mouth during certain events.

Fringing mangroves are present along the banks of the majority of the Skardon River. The mangrove vegetation will act to stabilise the sediment along the banks by attenuating both locally generated wind waves and tidal currents. The mangroves therefore help to create a depositional environment along the river banks. The presence of fringing mangroves throughout the estuary indicates that the banks of the river are currently stable and accreting.

Figure 17-5 Aerial Photograph of Skardon River from 1989


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17.4.11 Marine Water Quality

17.4.11.1 Water Quality Sampling

A combination of eight vessel based and logger based water quality physico-chemical and chemical marine water quality investigations have been undertaken within the Skardon River since 2011. These events captured a combination of dry season and wet season data sets (Table 17-3). In addition to vessel based surveys, two data loggers were deployed within the Skardon River adjacent to the existing barge ramp (Port infrastructure area) and upstream of the Port area during 2011. The objective of the program was to record time series water quality data over the 2011/2012 wet season. At least 16 locations were sampled with sampling locations shown in Figure 17-6 ranging from the ebb tidal delta beyond the mouth to upstream Skardon River South Arm. All data is presented in Appendix 8, with a summary provided below.

Table 17-3 Marine Water Quality Sampling

Date Source Sites Period Chemical Physicochemical

2011 PaCE 5 Oct, Nov, Dec, Jan Yes Yes

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2014 PaCE 5 Nov Yes Yes

2014 RPS 3 August Yes

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17.4.11.2 Turbidity

Mean surface turbidity (ntu) ranged widely between the grab sample survey periods (0 ntu to 30.6 ntu). The available dry season data reported a mean turbidity of 0 to 4.2 ntu, while the wet season data reported a mean turbidity of 30.3 ntu, indicating increased turbidity during the wet season in line with expectations. Comparisons made between turbidity, water depth and dissolved oxygen demonstrate the roll of tidal exchange in elevating turbidity and decreasing DO at the logger location. During the ebb tide, waters from tidal creeks and adjacent mangroves created an increase in turbidity and reported a decrease in available DO. The data shows short lived elevations above 3000 ntu, though the majority of reading remain less than 500 ntu, dropping to 0 ntu or near 0 ntu following the change in tide.

17.4.11.3 Salinity

During the wet season, salinity from the Skardon Rivers upper estuary reported concentrations between 24-26 part per thousand (ppt). These concentrations increased nearer the river entrance reporting 30-32 ppt. During the dry season this salinity trend reverses, with a salinity maximum being developed within the upper reaches. The salinity maximum is developed from a reduction in freshwater inflows, restricted tidal flushing and an increased evaporation rate within the shallow waters and mangrove systems of the upper estuary system. Towards the end of the dry season salinity within the upper reaches ranged between 30-42 ppt, while the mid and entrance reaches ranged between 27-37 ppt.

During the dry season the ebbing tide pulls higher salinity waters from the upper estuary and shallow water environments of the mangroves into the river channel. Upon the turn of the tide, incoming waters from the lower estuary introduce lower salinity waters. This processes recorded salinity variations between 33-35 ppt over three tidal cycles.

17.4.11.4 pH

The Skardon River presents a pH range of 7-8 within the entrance and lower estuary, reducing as sites progress up the estuary and beyond the existing barge facility (6.9-7.5). Very strong spatial and temporal trends have been identified. As the flooding tides push through the existing Port area pH increases from ~7.3 to 8.1. As tides begin to ebb, reduced pH waters are extracted from the mangroves and creek systems to the primary channel. The roll of increased biological activity and contact with intertidal sediments within the mangroves acts to alter a broad range of physicochemical parameters. These processes keep the Skardon River in a continual process of chemical change.

17.4.11.5 Dissolved Oxygen

Dissolved oxygen within the Skardon River demonstrates a distinct spatial trend, reducing as distance from the entrance increases. This trend is driven by several factors, including a reduction in flushing capacity as locations move upstream from the entrance, and an increased organic load within the river channel. Seasonal changes in freshwater flow between the wet and dry seasons also influence DO.

Smaller scale temporal variability has also been recorded with a high correlation between DO and tidal exchange. As the tide drops, water from the upper estuary and adjacent mangrove systems is pulled into the primary river channel. These waters have been exposed to increased organic processes, high organic loads and increased turbidity. DO was observed to reduce markedly. As the tide changes, freshwater from the lower reaches is pushed into the upper estuary providing increased DO to the mangrove systems. Due to the elevated organic load, the DO experienced within this time series record is exceptionally low for natural systems.

Oxidation reduction potential (ORP) follows similar trends displayed by dissolved oxygen and pH.


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17.4.11.6 Nutrients

Nutrient levels were compared to the Australian and New Zealand Environmental Conservation Council (ANZECC) water quality guideline trigger values for tropical systems.

Total nitrogen (TN) and total phosphorous (TP) concentrations remained well over the adopted ANZECC screening criteria. TN ranged between 2000 ug/Land 50 ug/L over the survey period, recording a mean concentration of 476 ug/L (ANZECC criteria 250 ug/L). TP ranged between 30 ug/L and 92 ug/L, recording a mean of 51 ug/L (ANZECC criteria 20 ug/L).

17.4.11.7 Metals

Arsenic and zinc recorded elevated concentrations compared to cadmium, chromium, copper, lead and nickel. A natural ratio between these metals concentrations was clearly observed. While concentrations may vary between locations, the ratios between metals at each site remain relatively consistent over the sampling period. Copper and zinc recoded metal concentrations in excess of the ANZECC criteria. Similar trends in ratios are reflected in analysis for aluminium and iron (no ANZECC criteria available for these metals). While concentrations may be elevated for some analytes, the broad maintenance of these ratios across all locations is indicative of natural ambient conditions, rather than being induced by anthropogenic sources.

17.4.11.8 Chlorophyll-a

Chlorophyll-a concentrations remained marginally above detection at 1-2 ug/L.

17.4.11.9 Hydrocarbons

The full suite of hydrocarbons (C6-C36) remained non detectable from all survey locations during both the wet and dry seasons.

17.4.11.10 Summary

Key findings include:

There is very high natural variability in turbidity in the Skardon estuary.

Salinity within the Skardon River is dependent upon season (wet/dry) and distance upstream from

the entrance. During the wet season, increased freshwater flows from the catchment act to reduce

salinity within the river, mixing with higher salinity waters entering through the river mouth. During

the dry, increases in salinity are recorded.

The Skardon River presents a pH range of 7-8 within the entrance and lower estuary, reducing as sites

progress up the estuary and beyond the existing barge facility (6.9-7.5). There is a strong correlation

between tides and pH.

Dissolved oxygen reduces as distance from the entrance increases. There is a high correlation

between DO and tidal exchange.

Total nitrogen and total phosphorous concentrations remained well over the adopted ANZECC

screening criteria within the Skardon River during the survey period.

The metals suite identified several elevations in metals, including copper and zinc compared to the

ANZECC criteria. Similar trends in ratios are reflected in analysis for aluminium and iron.

The full suite of hydrocarbons (C6-C36) remained non detectable from all survey locations during both

the wet and dry seasons.

Despite an absence of any substantial anthropogenic inputs, background water quality has recorded elevations in nutrients (total nitrogen and phosphorus) and metals (zinc and copper) as compared to the


-14

ANZECC criteria. These findings are considered a function of natural processes within northern tropical systems, rather than influences from contamination or catchment based affects.

Water quality conditions of the Skardon River exhibit no problematic affects associated with historical or existing land use, and the system is considered ‘near pristine’ with respect to water quality. In the absence of adjacent anthropogenic inputs, naturally occurring elevations in nutrients (nitrogen and phosphorous) and some metals are considered a feature of these biologically productive, turbid and tidally dominated tropical estuary systems. Reductions in dissolved oxygen and variability in salinity, turbidity and ORP are considered representative of the naturally occurring processes of the Skardon River.

17.4.12 Water Quality Objectives

The Skardon River Bauxite Project is situated within the Gulf Rivers province, as described within the Queensland Water Quality Guidelines (QWQG). Marine and estuarine water quality criteria have not yet been established for the Skardon River.

Due to the unique and naturally variable marine environment of the Skardon River, development of site specific water quality objectives will be considered prior to construction and operational activities being undertaken. Ongoing water quality monitoring will aid in developing water quality objectives for the Skardon River.

Water quality data analysis identifies significant differences between key reaches of the river and at different times linked to tidal cycles and seasons. Such features may lead to establishing multiple criteria within the river system for some parameters based on spatial areas, tides and seasons. This may mean that water quality criteria will be established for several zones, potentially upstream, mid and downstream locations.

Preliminary water quality objectives have been developed based on the analysis of the 80th percentile from 5 locations in the Skardon River sampled over 5 events (total of 25 replicate samples), and are shown in Table 17-4 along with comments about their relevance to the Skardon River.

Table 17-4 Preliminary Water Quality Objectives

Parameter Unit Objective Comment

Physicochemical

Dissolved oxygen % 80-120 Ambient condition range widely from these standard concentrations, particularly within the upper estuary. Development of site specific criteria is recommended as part of long-term marine monitoring. Spatial consideration in criteria is required.

pH 7-8.5 Applicable

Salinity To be advised (TBA

The presence of a salinity maximum has been identified within the upper estuary. This alters between seasons so that seasonal criteria may also be required. Spatial consideration in criteria is required.

Redox potential TBA Redox potential within the upper estuary is influenced by a significant organic load. Spatial consideration in criteria is required.

Temperature na Temperature is not considered a significant parameter regarding compliance in ambient waters.


Page 17-15

Parameter Unit Objective Comment

Turbidity NTU 1-200 Ambient conditions are seasonally elevated above these criteria in several of the samples, particularly from the in situ logger data. Development of site specific criteria is recommended as part of long-term marine monitoring. Spatial consideration in criteria is required.

Nutrients

Ammonia mg/L 15 ug/L The standard ANZECC criteria are substantially lower than the conditions screened from the Skardon River at present. Development of site specific criteria is recommended as part of long-term marine monitoring. The 80th percentile have been provided for total nitrogen and total phosphorus. Other parameters may also require adjustment as additional data is collected prior to construction.

An extended water quality program will likely reduce adopted nutrient targets.

Nitrite mg/L 30 ug/L

Nitrate mg/L 30ug/L

Total Kjeldahl nitrogen

mg/L na

Total nitrogen µg/L 1000

Reactive phosphorous

µg/L 5

Total phosphorus µg/L 60

Metals

Aluminium µg/L 220 The standard ANZECC criteria are largely applicable for use in monitoring. However, long-term programs may also consider developing an improved understanding of ambient conditions to develop site specific criteria. The 80th percentile has been adopted within this table. Zinc and copper displayed elevations above the standard ANZECC criteria at the 95th percentile. Other parameters may also require adjustment as additional data is collected prior to construction. Nutrient values appear elevated from the existing available data and criteria will likely decrease as data develops.

Arsenic µg/L 92

Cadmium µg/L 0.35

Chromium µg/L 4.9

Copper µg/L 3.9

Iron µg/L 274

Manganese µg/L na

Mercury µg/L 0.1

Nickel µg/L 12.5

Lead µg/L 2.5

Zinc µg/L 38

Biological

Chlorophyll-a mg/m3 2 The standard ANZECC criteria are largely applicable for use in monitoring. However, long-term programs may also consider developing an improved understanding of ambient conditions to develop site specific criteria. The 80th percentile has been adopted within this table.

Hydrocarbons

C6-C36 mg/L 0 Any presence of hydrocarbons within the waters of the study area is not expected. Sampling as part of operational monitoring is recommended.


Page 17-16

17.4.13 Sediment

The sediments of the Skardon River are largely unimpacted by development or anthropogenic processes, with very limited impact from historical kaolin operations. Sediment investigations have been undertaken in 2014 and 2015 in the Skardon River, mouth of the Skardon River (bed levelling area) and offshore transshipment area.

The concentration of bauxite resources within the area presents a potential source of naturally occurring metals, particularly iron and aluminum, and elevations in minor trace metals may also be present.

17.4.13.1 Sediment Sampling

Several recent sediment investigations have been commissioned by Gulf Alumina and Metro Mining within the Skardon River, as summarised in Table 17-5, with information shared between these companies. These investigations provide background data regarding chemical characteristics of the system and particle size distribution. A key area for investigation was the bed levelling area where a more detailed investigation of sediments in the Skardon River entrance has been conducted in accordance with the Commonwealth’s National Assessment Guidelines for Dredging (NAGD). Sediment sampling locations are shown in Figure 17-6. Further information on sediment sampling is provided in Appendix 8.

Table 17-5 Sediment Sampling

Source Survey Period Location/sites Analysis Method

RPS September, 2014 Gulf – Port area (1) River entrance (2) Offshore transshipment area (3)

Metals ASS PSD

Surface grab

PaCE November, 2014 Metro barge facility (5) Metals PSD

Surface grab

RPS March, 2015 Upstream of Port area (2) Gulf – Port area (2) Skardon River (2) River entrance (2) Inshore (1)

pH Nutrients Metals ASS

Surface grab

PaCE April, 2015 River entrance (13) Metals Nutrients PSD

Piston core 0-0.5m – 0.5-1.0m

17.4.13.2 Particle Size Distribution

Analysis for particle size (gravel, sand, silt/clay) shown in Figure 17-7 depicts a general decrease in silt and clays and increase in sands as locations progress from upstream to downstream (from left to right in Figure 17-7) locations nearer the river entrance. Entrance and offshore samples confirm a dominant sand profile.


Page 17-17

Figure 17-7 Particle Size Distribution

17.4.13.3 Metals

A suite of metals have been analysed throughout the Skardon River and adjacent offshore sediments (refer Appendix 8). Mean concentrations of metals have been compared to the ANZECC (2000) Interim Sediment Quality Guideline (ISQG) screening criteria (ANZECC/ARMCANZ, 2000).

With the exception of arsenic, at the proposed wharf and within the upper estuary, the mean of all other analytes remained below the ANZECC screening criteria. Arsenic concentrations within Queensland’s coastal catchments may attain natural elevations due to the mineralogy of the adjacent catchments.

Iron and aluminum also both display strong spatial trends in concentration. Both iron and aluminum decrease markedly between upstream and downstream locations. Offshore sediments present the lowest recorded concentrations.

All metals analytes from the sediment investigations from the proposed bed leveling footprint reported concentrations well below the relevant NAGD criteria. Individual samples also maintained concentrations below these criteria. The sediments within the proposed bed levelling area do not present a risk of contamination from the bed levelling process.

17.4.13.4 Nutrients

Nutrients (total nitrogen and phosphorous) have been analysed within the Skardon River throughout the length of the estuary system. Nutrients show a general decline in concentration between upstream locations and the river entrance. The distribution and concentration of sediment nutrients often display strong relationships with sediment particle size. Silt and clay fractions within the Skardon River demonstrate a significantly increased retention of nutrients compared to the sand fraction.

Sediments from proposed bed leveling areas represent a range of coarse sands and gravels to fine sands and silts. Finer sediments tend to present an increased nutrients profile. The sediments within the entrance present little in the way of nutrient release potential.

17.4.14 Acid Sulphate Soils

Limited acid sulfate soils potential has been screened both onshore (Metro Mining) and within the sediments of the Skardon River.

Sampling for acid sulphate soils has been undertaken as:

a screening for marine sediments at 10 locations within the Skardon River (the same locations for

marine water quality and sediment sampling)

two core samples approximately 250 m and 2 km upstream of the proposed wharf.


Page 17-18

Available data has been screened for acid sulfate soil under the Guidelines for Sampling and Analysis of Lowland Acid Sulfate Soils (ASS) in Queensland (QASSIT Guidelines) (QASSIT, 1998).

The ten (10) surface sediment samples (river bottom and banks) were submitted for acid sulphate soil assessment, extending from the upper river reaches to the entrance and immediate offshore sediments. Results are presented in Appendix 8. Based on these samples, any marine sediments disposed to land (not proposed for the Project) may present a risk of potential acid sulphate soils (PASS) impact and risk of acid leachate generation.

The site approximately 250 m upstream of the wharf approximates the conditions which may be representative of the conditions surrounding the wharf. At both coring sites, triplicate sampling was undertaken from each location to a depth of 6.0 m. Results are presented in Appendix 8. Sediments outline a low acid sulfate soil potential. Never-the-less, where soil excavation is proposed, consideration of risks from acid sulfate materials will be incorporated into the development design.

Additional information on acid sulphate soils is presented in Chapter 10.

17.5 Potential Impacts

The potential impacts on coastal processes and the physical marine environment are a function of:

Port construction

bed levelling

shipping operations within the Skardon River and near shore

offshore transhipment of bauxite

bulk vessel movements

changes to water quality as a result of mining and Port activities

17.5.1 Port Construction

The selection of piling construction over infill construction or causeway methods for wharf infrastructure presents a significant impact minimisation measure as:

short term and long term impacts associated with permanent habitat loss are significantly reduced

hydrological regimes are not impacted to any significant extent

interaction with acid sulphate soils and potential acid sulphate soils is minimised

the open design structure will also allow the passage of tidal waters and seasonal flood flows

passage of fauna residing in and adjacent to the mangrove habitats will not be substantially

constrained

the fisheries resource values of the Project area are maintained.

No dredging is proposed in the Port area for loading export barges or handling supply vessels. Depths at the proposed wharf facility are sufficient, and deepening of the barge berthing pocket is not required. This design measure results in significantly less disturbance to the marine environment at the Port.

17.5.2 Bed Levelling

The process of bed levelling will be undertaken on the ebbing tide to favour the dispersion of any potential turbidity plumes offshore.


Page 17-19

17.5.3 Offshore Transhipment

The offshore transhipment area location was selected on the basis of benthic habitat and sediment surveys which identified very low density benthic communities and sediments that are sand dominant. This location will minimise impacts to marine ecology from offshore anchoring and bauxite transhipment.

Offshore transhipment of bauxite from barges to bulk vessels will not involve any permanent structures in the marine environment and therefore there are expected to be negligible impacts on coastal processes and the physical marine environment. Potential impacts on benthic habitat in the offshore transhipment area are described in Chapter 18.

17.5.4 Bulk Vessels

Bulk vessel movement will not impact coastal process or the physical marine environment. Further information about the potential bulk vessel impacts on marine ecology and Commonwealth marine waters is provided in Chapter 18.

17.5.5 Hydrodynamics

Due to the relatively small scale of the proposed development the hydrodynamic impacts expected would be small localised changes to the tidal currents.

Impacts from Port development will be small and restricted to the areas directly adjacent to the structures and as the area already has marine port facilities present, the impacts on coastal processes are not considered to be significant.

The bed levelling activity involves moving sand from peaks into adjacent troughs and will not result in any absolute change in volume of material in the channel and therefore will not change the discharge through the channel. Two areas have been identified as requiring bed levelling, covering a total distance of 1.58 km (based on the 2009 hydrographic survey) of the channel offshore from the entrance. To reach the required bed level of -2.2m LAT (approximately -4.4m mean sea level (MSL)) the maximum deepening in the two proposed bed levelling areas is 0.95 m, which represents an increase in depth of approximately 20% relative to MSL. Based on this it is expected that the bed levelling will cause some localised changes to the tidal currents, with a reduction in current speeds where sediment is removed and an increase in tidal currents where material in deposited. The levelling of the channel bed will act to reduce the spatial variability in the currents along the channel as it makes the channel bathymetry more uniform. As the impacts from the bed levelling on the tidal currents will be very localised and as the activity will not change the discharge through the channel (because it is not changing the volume of sediment in the channel) the impacts to tidal currents are not considered to be significant.

The proposed development is not expected to have any impacts on the discharge from the Skardon River as there is no change to the tidal prism (volume of water in the estuary between mean high water and mean low water) of the river.

17.5.6 Sediment Transport

The bed levelling activity will have a direct impact by disturbing the sediment on the seabed and an indirect impact from increased suspended sediment concentrations and a resultant sediment plume throughout the duration of the activity. As this activity will be relatively short in duration (120 days for initial bed levelling and 60 days for maintenance bed levelling) and only occur annually the indirect impact of the increased suspended sediment concentrations is considered temporary. The direct impact of disturbing the sediment on the seabed would also impact the sediment transport and would be permanent for the duration of the Project (10 years).

As the sediment in the bed levelling areas is predominantly made up of gravelly sand, the resultant suspended sediment concentrations are expected to be relatively low (<50mg/l) away from the bed


Page 17-20

levelling activity and the plume relatively localised (within approximately 1,000 m), with the gravel and coarser sand settling out soon after being suspended.

The change in bathymetry due to the bed levelling will result in localised changes to the tidal currents, with a reduction in current speeds where sediment is removed and an increase in tidal currents where material is deposited. However, as the changes in current speed are likely to be relatively small it is expected that any subsequent changes to the morphology will be slow.

Siltation in the bed levelled areas above the required -2.2m LAT level is expected to be relatively slow during calm conditions in the dry season, but could be rapid during extreme cyclone and monsoon storm events in the wet season. Therefore, the proposed annual maintenance bed levelling after the wet season is likely to be required.

It is anticipated that the natural tidal flows and seasonal processes of flood flows and episodic cyclone/monsoon storm activity will act to restore pre-development conditions once mining operations have ceased.

17.5.7 Shoreline and Bank Evolution

Although the bed levelling will influence the local sediment transport in the two proposed bed levelling areas, it is not expected to result in a noticeable change to the longshore drift. Despite the bed levelling the shoals and delta will continue to act as stores of sediment and will allow sediment transported by longshore drift to bypass the river mouth during certain events such as periods of higher wave activity. As such, bed levelling is also not expected to influence the shoreline evolution of the coast to the north and south of the Skardon River.

The continuous barging of the bauxite from Skardon Port to the offshore transhipment location will result in the generation of vessel wake waves within the Skardon River. As mangroves are present along the majority of the banks of the Skardon River any vessel wake waves are expected to be attenuated by the established mangrove vegetation. However, due to the presence of vessel wake waves in an area where little wave energy occurred previously there is a risk that erosion of some more exposed areas of the river bank could occur.

17.5.8 Morphology

The bed levelling activity would have a small, direct but temporary (for the 10 year duration of the Project) impact on the morphology of the channel offshore of the entrance to the Skardon River. The morphological assessment of the existing environment shows that the proposed bed levelling activity is in line with the existing natural morphological evolution of the features and the proposed changes in bed elevation are within the natural range. The local changes in bathymetry from bed levelling are not expected to result in any regional changes to the morphology of the complex bathymetry offshore of the Skardon River mouth as sediment is not being removed from the system. In addition, a rapid recovery of the natural system and morphology would be anticipated following cessation of the bed levelling activity at the close of the Project with no ongoing impacts.

17.5.9 Water Quality

Some minor water quality impacts are likely to be encountered during both Port construction and operations. The processes of wharf construction and development across intertidal areas will impact water quality over the short term. Key imposts to long-term water quality during operation will include, potential dust emissions during the loading process, barge and vessel movements (prop wash), potential spills and chemical release (including hydrocarbons/fuels). Benthic communities and seagrass may be present near the wharf construction area (refer Chapter 18).

The process of bed levelling within the entrance shoals will mobilise fine sediments during operations. However, it is noted that the sediments within the entrance are dominated by gravel and sand fractions,


Page 17-21

within increasing fine sands and silts/clays offshore. Given an absence of benthic habitats around the entrance, and an adopted ebb tide only approach to bed levelling, impacts from turbidity increases are expected to be minor. The chemical nature of the sediments from the entrance does not present a risk of contamination to marine biota or impact to water quality.

The water quality sampling demonstrated broad fluctuations in ambient water quality, including turbidity. The proposed onshore water management plan, hydrocarbon controls, the absence of dedicated discharges or ongoing polluting processes from chemical release from the Project, and the broad ambient fluctuations in water quality, will limit water quality impacts from the Project.

17.5.10 Sediment

Onshore mining has the potential to impact water quality through the release of sediments to the marine environment. Port activities have the potential to impact marine water quality through the accidental release of hydrocarbons, fuels and chemicals, sediment runoff and dust emissions.

Operation of barges and supply vessel may be expected to generate prop wash as sediments are mobilized from the bottom in shallower waters. The prevalence of sands within the sediment matrix suggests that impacts would be short lived with the bulk of mobilized materials resettling to the channel areas.

The sediments of the Skardon River represent ambient conditions and display little evidence of historical contamination. Concentrations do not represent a substantial risk to water quality following mobilisation, and contaminant effects as a result of sediment mobilisation during construction and operation are not anticipated. The mobilization of sediments from prop wash represents a similar minimal disturbance process. The greatest potential for sediment mobilization is during bed levelling. Concentrations of metals contaminants within the bed levelling areas do not represent problematic levels and impacts outside turbidity elevations are not anticipated.

Minor spillages of fuels or chemicals may be expected during construction and operations. However, standard practices for chemical spill and cleanup would be sufficient to address such incidents.

Regular monitoring of sediments within the proposed wharf footprint, barge route and offshore transhipment area will be undertaken as part of operational management processes. This screening process will be undertaken as a baseline (pre-construction survey) and repeated annually to confirm operational processes are not leading to impacts of the surrounding sediments.

Monitoring may also include video or still imagery, to define the occurrence of operational spillages of bauxite during loading and unloading. While not a chemical contamination process, spillages to the environment will be minimised, and amendments to loading equipment or processes made if such events are occurring on a repetitive basis.


Sampling for acid sulfate soils indicates some minor potential of ASS and slightly greater PASS generation from sediments if disturbed and exposed to oxidation. The river based sampling confirms an absence of ASS though these sediments presented elevated PASS concentration within the upper estuary and adjacent to the existing Port.

Sediments within the proposed wharf areas have the potential to create acid drainage problems should these be exposed to oxygenated conditions or oxygenating processes. However, given the proposed piling construction methods the risk is considered low. The Queensland Acid Sulfate Soil Technical Manual: Soil Management Guidelines identify piles as a low impact construction method for ASS impacted areas. Australian Standard AS2159-1995 − Piling Design and Installation (Standards Australia, 1995) provides guidance on the use of piles in soils that contain pyrite or are saline.


Page 17-22

17.6 Mitigation Measures

17.6.1 Vessel Wakes

Wherever possible existing native riparian vegetation around the Port will be maintained to minimise any impact to bank stability, water quality and habitat loss at the Port location. This is especially important for mangrove vegetation as it will help to prevent bank erosion due to locally generated wind waves and vessel wake waves from the barges.

Further assessment of the potential impacts of vessel wake waves may be undertaken prior to the Project commencing to better understand potential impacts and highlight areas at risk. River bank position and bank vegetation monitoring will be undertaken to indicate any potential changes resulting from the vessel wake waves. Locations for bank erosion monitoring (use pre and post photo monitoring and sediment monitoring) will be selected throughout the estuary so as to encompass a broad range of shorelines and proximities to vessel traffic.

Suitable vessel speed restrictions will be imposed to minimise any potential increased bank erosion due to the barging activity. This will be defined based on Port safety considerations, and on the barge vessel size and capacity as well as the transport frequency. The marine vessel operations plan, including vessel speed and access plan is described in Chapter 22.

Vessel access and navigation channels will be defined so that vessels remain within the deep water navigation channels during transit.

17.6.2 Bed Levelling

Bed levelling depth has been selected to minimise direct impacts on the sea bed sediments but allow for efficient operation of barges. Sediment with a maximum depth of 2.2 m below LAT is proposed to be relocated for the initial bed leveling campaign. The 2009 bathymetric surveys show that the natural bed level of the Skardon River is at least 1.1 m below LAT. Hence to achieve a bed levelling depth of 2.2 m below LAT, a maximum depth of bed levelling of approximately 1.1 m is required with an average bed levelling depth of approximately 0.5 m.

Bed levelling will be relatively short in duration (120 days for initial bed levelling and 60 days for maintenance bed levelling) and will occur annually.

Bed levelling activities will be undertaken during the ebb tide to ensure that any suspended sediment resulting from the activity is transported offshore and not into the estuary. This would also act to replicate the natural offshore migration of bedforms which has been observed. The bed levelling will aim to relocate material in a westerly direction wherever practical to replicate the natural bedform migration and to help minimise the requirement for repeat bed levelling. During bed levelling, the dispersion of turbidity plumes will be monitored.

17.6.3 Barge Operations

The channel offshore of the mouth of the Skardon River will be hydrographically surveyed, as required for safe navigation, and typically annually at the end of the wet season.

Proposed barge activities will not occur during the wet season (mining shut down period) due to the potential for extreme weather events over this period. In addition, the barge activities will not recommence until after the hydrographic survey has been undertaken and any maintenance bed levelling completed at the start of the dry season to ensure the offshore channel is navigable.

The marine vessel operations plan, including vessel speed and access plan is described in Chapter 22.


Page 17-23

17.6.4 Prop Wash

Vessel movements will be controlled to minimise prop wash (refer Chapter 22). Vessel passage over or immediately adjacent to seagrass habitats will be limited. Defined shipping routes, following the vessel access plan will be used.

17.6.5 Bauxite Loading

The conveyor and chute barge loading systems will be designed to minimise spillage of bauxite by directing bauxite directly to barges. Losses during transhipment will be recorded and reported. Monitoring of sediments is described in Section 17.5.10.

17.6.6 Water Quality

Management measures to prevent or minimise the release of contaminants from the Port infrastructure, including hydrocarbons, fuel, chemicals and wastes are described in Chapter 11.

Port area sediment management, including design, construction and operation of Port sediment ponds is described in Chapter 6.

Management measures to prevent and minimise sedimentation of the marine environment from mining activities are described in Chapter 6 and Chapter 12.

Wetland buffers zones (including buffers to marine wetland areas) are described in Chapter 16. A wetland buffer zone is proposed along the Skardon River South Arm supratidal wetland, which will provide at least 100 m separation distance between mining and wetland areas. This buffer zone will also act to contain any sediment runoff from mining.

Dust management measures are described in Chapter 19.

Commercial vessels involved in the site construction and operational phases will be subject to international, national and state policies and guidelines to restrict environmental impacts as a result of spillages, anticorrosion products, wastewater products, and solid wastes. Marine transport and operations management, including pollution controls and oil spill response plan are described in Chapter 22.

The following plans have been produced for the management of the Port of Skardon River:

Oil Spill Contingency Plan (Ports Corporation Queensland, 2003)

First-Strike Oil Spill Response Plan - A supplement to the Queensland Coastal Contingency Action Plan (MSQ, 2005)

Port Rules (Ports North, 2015)

These plans will be reviewed in conjunction with Port North and updated as required to meet Project requirements. Marine transport and operations management, including pollution controls and oil spill response plan are further described in Chapter 22.

During construction in the marine environment, the following mitigation measures are proposed:

Monitor turbidity, deposition and benthic light availability during construction and amend work practices if required.

Time marine construction works during spring tidal periods, where practicable where materials are dispersed a greater distance, and deposition impacts are minimised.

Sediment curtains may be used during periods of activity where substantial sediments may be disturbed.


Page 17-24

The need for these sediment controls will be informed by water quality monitoring.

Preliminary marine water quality objectives are described in Section 17.4.12. A marine water quality monitoring program will be implemented, which includes:

monitoring of marine water quality prior to construction and operations to improve the

understanding of spatial and temporal (tidal and seasonal) water quality

monitoring of water quality at seagrass habitats during Port construction, potentially on a weekly

basis

wet and dry season monitoring within the Skardon River to provide spatial representation (e.g.

upstream of Port, downstream of Port, mid-stream and mouth)

monitoring of water quality during bed levelling, in response to sediment plumes

monitoring in response to any accidental release of hydrocarbons, fuels or chemicals.

The pre-construction monitoring program will inform establishment of site specific water quality criteria following the QWQG. The monitoring program will include a combination of vessel based monitoring locations and time series data loggers deployed over seagrass habitats within the proposed development area. Baseline monitoring will be undertaken quarterly prior to and during operations.

Parameter’s for analysis will include those in Table 17-4, including relevant physicochemical parameters, nutrients, metals, hydrocarbons, total suspended solids and chlorophyll-a. Time series loggers will include turbidity, deposition and light availability (PAR).

Pre-construction monitoring will define ambient water quality objectives. Sites will be selected to provide spatial representation of marine water quality for an ambient program, and more detailed impact assessment over adjacent seagrass communities during construction.

Monitoring data will be used to assess whether the Project is impacting marine water quality, whether remediation / management measures are required to protect environmental values and to inform regulators as required.

The surface water monitoring programme described in Chapter 12 includes monitoring locations, frequencies and parameters for the Skardon River, which are repeated in Table 17-6.

Table 17-6 Marine Water Quality Monitoring

Monitoring Point

Location Details Site Function – Bauxite Project#

Easting (m)

Northing (m)

Frequency Parameters

S15 Skardon River South Arm – estuarine water – downstream of Pit 3 and upstream of Port.

Reference site prior to mining. Compliance site once mining commences.

615996 8694458 Quarterly Physico-chemical, nutrients, metals

S16 Skardon River South Arm – estuarine water – downstream of all pits (Pits 1, 2, 3, 6) and upstream of Port.

Compliance site once mining commences.



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Monitoring Point

Location Details Site Function – Bauxite Project#

Easting (m)

Northing (m)

Frequency Parameters

S17 Skardon River South Arm – estuarine water – downstream of Port

Reference site prior to mining. Compliance site once mining commences.


# Tidal ebb and flow may result ‘upstream’ monitoring locations being the compliance site and ‘downstream’ reference sites

being the reference site.

Proposed water quality objectives for monitoring parameters in the marine environment are described in Table 17-4.

If water quality characteristics from monitoring of compliance locations during operations exceed any of the water quality objectives specified in Table 17-4 then Gulf will compare the monitoring results in the compliance sites to monitoring results from reference sites and:

where the reference site results are not exceeded then no action will be taken, or

if the result is greater than the reference site, complete an investigation into the potential for

environmental harm and provide a written report to the administering authority in the next annual

return outlining:

details of the investigations carried out

actions taken to prevent environmental harm.

The following information will be recorded for all water monitoring:

the date on which the sample was taken

the time at which the sample was taken

the monitoring point at which the sample was taken

the results of all monitoring and details of any exceedances of the conditions of the EA.

17.6.7 Sediment Quality

The measures described to manage impacts to water quality will also minimise impacts to marine sediment quality.

Monitoring of sediments within the proposed wharf footprint, barge route and offshore transhipment area will be undertaken as part of operational management processes. This screening process will be undertaken as a baseline program (pre-construction) and repeated with sufficient regularity to confirm operational processes are not leading to significant impacts of the surrounding sediments.

Monitoring may also include video or still imagery, to define the occurrence of operational spillages of bauxite during loading and unloading. While not a chemical contamination process, spillages to the environment will be minimised, and amendments to loading equipment or processes made if such events are occurring on a repetitive basis.

Monitoring data will include metals, hydrocarbons (C6-C36), PAH’s, nutrients, particle size analysis, total organic carbon and moisture.

Monitoring data will be used to assess whether the Project is impacting marine sediment quality, whether remediation / management measures are required to protect environmental values and to inform regulators as required.


Page 17-26


Once the footprints for wharf facilities are defined and construction methodologies finalised, an additional field investigation will be undertaken to identify ASS or PASS and if required, support the preparation of an ASS Management Plan. Should a detailed ASS Management Plan be required, then additional analysis within the construction footprint would be undertaken in accordance with the QASSIT Guideline.

Construction activities at the site will be undertaken outside of the wet season period, which will reduce the potential for erosion, off site transport of sediments and generation of acidic leachate. Clearing of mangrove vegetation and disturbance of marine muds during construction of the conveyor alignment may disturb sediments recognized to contain PASS. Care will be taken to ensure disturbed sediments remain below the tidal inundation zone so exposed materials do not become reactive.

17.7 Risk Assessment

A risk assessment assessing the likelihood and significance of impacts to coastal processes and the physical marine environment from the Project is provided in Table 17-7. The risk assessment considers mitigated risk; that is, the impact from the Project with the implementation of management measures. The risks to coastal processes and the physical marine environment are low.

Table 17-7 Risk Assessment and Management Measures for Impacts to Coastal Processes and the Physical Marine Environment

Environmental Value

Impacts / Emissions / Releases

Proposed Management Practices

Likelihood Consequence (Magnitude)

Risk Rating

Hydrodynamics Port construction. Refer Sections 17.5.1 and 17.5.5.

Refer Section 17.6

Unlikely Minor Low

Bed levelling. Refer Sections 17.5.2 and 17.5.5.

Refer Section 17.6

Possible Negligible Low

Shoreline and bank evolution

Barge movements. Refer Section 17.5.7

Refer Section 17.6.1

Possible Negligible Low

Bed levelling Refer Section 17.5.7

None proposed

Rare Minor Low

Morphology Bed levelling. Refer Section 17.5.8

None proposed

Rare Minor Low

Sediment transport

Bed levelling. Refer Section 17.5.6

Refer Sections 17.6.2 and 17.6.7

Unlikely Minor Low

Marine water quality

Onshore mining. Refer Section 17.5.9


Unlikely Minor Low

Port area operations. Refer Section 17.5.9


Unlikely Minor Low

Wharf construction. Refer Section 17.5.9


Unlikely Minor Low


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Environmental Value

Impacts / Emissions / Releases

Proposed Management Practices

Likelihood Consequence (Magnitude)

Risk Rating

Bed levelling. Refer Section 17.5.9


Unlikely Minor Low

Sediment quality

Onshore mining. Refer Section 17.5.10


Unlikely Minor Low

Port area operations. Refer Section 17.5.10


Unlikely Minor Low

Barge operations / prop wash. Refer Section 17.5.10

Refer Sections 17.6.4 and 17.6.7

Possible Insignificant Low

Bauxite loading. Refer Section 17.5.10

Refer Section 17.6.5 and 17.6.7


Acid sulphate soils

Refer Section 17.5.11 Refer Section 17.6.8


17.8 Cumulative Impacts

The only project considered to have a cumulative impact to coastal processes and the physical marine environment with the Skardon River Bauxite Project is Metro Mining’s Bauxite Hills project. This project will have similar impacts to the Skardon River Bauxite Project as it will involve Port construction (approximately 2 km upstream of the existing Port), mining of bauxite from areas surrounding the Skardon River, barging of bauxite and offshore transhipment of bauxite to bulk vessels. The Bauxite Hills project does not propose bed levelling.

The construction process for both projects is very similar with regards to barge infrastructure. A short construction period during the dry season is proposed for both projects. This would include pile based construction and an increased vessel traffic for construction and operation. Due to separation distance between ports and low potential for simultaneous construction periods, cumulative impacts are likely to be low.

The operational scenario would present a substantial increase in vessel traffic should both projects overlap. To meet the basic annual tonnages and weekly bulk carrier loading targets, up to 100 barge movements would be required within the Skardon River each week (3600 - 4000 movements annually) (in comparison, the Port of Weipa experiences approximately 900 to 1000 movements along the channel (in and out) annually. These movements would be accompanied by additional movements associated with fuel and materials supply.

17.8.1.1 Skardon River

Should both projects occur over the same period, or overlap to some extent the Skardon River would be exposed to significant vessel traffic. The impacts to coastal processes and the physical marine environment associated with such traffic volumes include potential bow wave and wake impacts, propwash turbidity, water quality impacts and navigation safety.

Cumulative impacts upon water quality due to construction and operational spillages or releases may be anticipated, but following standard mitigation practices and operational standards any increase would be


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of a minor concern. Cumulative impacts associated with construction may be of greatest concern should pile operations be undertaken together.

The barges exporting bauxite will provide the bulk of vessel movements for both projects. These vessels are relatively large and slow, operating in the range of 6-10 knts while offshore (4-8 knts, inshore).

As bed levelling is only proposed for the Skardon River Bauxite Project, there will not be cumulative impacts from multiple bed levelling operations.

17.8.1.2 Offshore Transhipment

The proposed offshore transshipment location for both projects are located several kilometers apart, though the passage for vessels exiting the Skardon River for the transshipment area will be relatively similar over most of its length. Bulk carriers will anchor within the transshipment areas and load bauxite from the barges. Gulf Alumina propose the use of self-unloading barges, Metro propose the use of deck cranes.

Potential impacts associated with the transshipment operation include any incidence of water quality or sediment impact associated with spills and releases (minor chemical spills, hydrocarbons and bauxite).

17.8.1.3 Bulk Carriers

Approximately 100 bulk carriers would be required to service both projects ach year. The nearby port of Weipa processes approximately 450-500 bulk carriers annually, exporting some 30 million tons of bauxite. The additional carriers required for the Skardon River Bauxite Project would represent a 10% increase in bulk carrier movements for the local area. A further 10% would be attributable to the proposed Bauxite Hills project.

Cumulative impacts on marine water quality, through ship-sourced pollution are possible. However it is expected that both operations will implement ship-source pollution prevention plans, including management of ballast water.

17.9 Conclusion

Surveys and monitoring have been undertaken for marine water quality, marine sediments and bathymetry of the Skardon River. Desktop reviews have been undertaken for the area potentially impacted by the Project, including published literature by third parties, other environmental studies for the EIS, environmental studies for other projects in the region, and historical data and reports from the Project area.

An assessment of coastal processes and the physical marine environment was undertaken for the Skardon River estuary, including the bed levelling area in the mouth of the Skardon River. The assessment includes tides, storm tide, tidal currents, river flows, bathymetry and morphology, shoreline and bank evolution, marine water quality, sediment and acid sulphate soils. Bathymetry and morphology was found to be relatively stable over the course of bathymetry surveys dating back to 1998. The channel alignment was constant with variation in depth of the channel at the river mouth attributable to localised sediment movements. Sediments in the bed levelling area are generally sandy. Water quality of the estuary, including turbidity is highly variable over tides and seasons.

Potential Project impacts on the marine environment include wharf construction at the Port, Port operations, bed levelling, vessel operations, offshore transhipment and bulk vessel movements.

Piling construction will be limited to approximately 2 months, with this method minimising disturbance in comparison to other wharf construction methods.

Bed levelling will occur annually at the end of the wet season. Bed levelling will be undertaken on the ebbing tide to favour the dispersion of any potential turbidity plumes offshore. Bed levelling impacts to


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tidal currents and river morphology are not considered to be significant. Suspended sediment concentrations are expected to be relatively low (<50 mg/l) away from the bed levelling activity and the plume relatively localised (within approximately 1,000 m), with the gravel and coarser sand settling out soon after being suspended.

As mangroves are present along the majority of the banks of the Skardon River any vessel wake waves are expected to be attenuated by the established mangrove vegetation.

The chemical nature of the sediments from the entrance does not present a risk of contamination to marine biota or impact to water quality. Concentrations of metals contaminants within the bed levelling areas do not represent problematic levels and impacts outside turbidity elevations are not anticipated. ASS investigations will be undertaken as required, although risk of exposure of ASS is low due to wharf construction methodology, and an ASS Management Plan prepared if required.

The primary management and mitigation measures for these impacts are:

vessel management, including speed and areas of operations

bed-levelling methodology

wharf design, using piles, which minimises hydrodynamic impacts and potential ASS impacts

no dredging in the Port area

design features to prevent spills of contaminants and response plans for spills of contaminants

compliance with ballast water management regulations

ongoing marine water quality and marine sediment monitoring

With the implementation of the proposed marine infrastructure design and construction, operational plans and mitigation measures, the risk of impacts to coastal processes and the physical marine environment is predicted to be low.

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