GRANGE RESOURCES ALBANY PORT AUTHORITY Port Development Oceanographic Studies and Dredging Program Simulation Studies July 2007 G LOBAL E NVIRONMENTAL M ODELLING S YSTEMS PTY LTD Australian Oceanographers & Ocean Modelling Software Developers ABN 28 061 965 339
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G R A N G E R E S O U R C E S
A L B A N Y P O R T A U T H O R I T Y
Port Development
Oceanographic Studies
and Dredging Program Simulation Studies
July 2007
G L O B A L E N V I R O N M E N T A L M O D E L L I N G S Y S T E M S P T Y L T D Australian Oceanographers & Ocean Modelling Software Developers ABN 28 061 965 339
GEMS – Global Environmental Modelling Systems Report 376/06
This report and the work undertaken for its preparation, is presented for the use of the
client. Global Environmental Modelling Systems (GEMS) warrants that the study was
carried out in accordance with accepted practice and available data, but that no other
warranty is made as to the accuracy of the data or results contained in the report. This
GEMS report may not contain sufficient or appropriate information to meet the purpose of
other potential users. GEMS, therefore, does not accept any responsibility for the use of
the information in the report by other parties.
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CONTENTS
GEMS Contact Details...........................................................................................................2 1. Introduction...................................................................................................................9 2. Scope of Work............................................................................................................10
2.1 Field Work .........................................................................................................10 2.2 Model Setup ......................................................................................................10 2.3 Verification of MesoLAPS winds, GCOM3D and SWAN in King George Sound
and Princess Royal Harbour ......................................................................................10 2.4 Simulations for a Representative Dredging Period ...........................................11
5.2.1 Extreme Wave Analysis ...........................................................................17 5.2.2 Waves Employed in the Current Study ................................................18
6. Field Work ..................................................................................................................19 6.1 ADCP Deployments ..........................................................................................19 6.2 Drifting Buoy Deployments................................................................................20
7.1.1 Data Sources.......................................................................................24 7.2 Analysis and Verification ...................................................................................25
7.2.1 MesoLAPS Validation..........................................................................25 7.2.2 Analysis of Wind Records ....................................................................25
9.1 Method ..............................................................................................................44 9.1.1 The Wave Model ..................................................................................44
11.1 The Effects of Changes to the Entrance to Princess Royal Harbour............54 11.1.1 Hydrodynamic Studies .......................................................................54 11.1.2 Numerical “Dye” Tracing Studies .......................................................56 11.1.3 Conclusions from the Hydrodynamic and Numerical “Dye” Tracing
Studies ............................................................................................................57 11.2 Waves along the Channel ............................................................................67 11.3 Spoil Ground Location ..................................................................................67
12.2.1 Total Suspended Solids ......................................................................77 12.2.2 Sedimentation ....................................................................................79
13. References .................................................................................................................91 Appendix A: Qualitative and Limited Quantitative Comparisons of DREDGE3D
Predictions with Data during the Geraldton Port Redevelopment Dredging Program .........92 A.1 Method.........................................................................................................92 A.2 Comparison of Predictions with TSS Measurements ..................................93 A.3 Comparison of Model Predictions with Satellite & Aerial Photos..................93 A.4 Outcomes ....................................................................................................94
Appendix B: Model Descriptions.....................................................................................100 B.1 GCOM3D....................................................................................................100
B.1.1 History and Physics...........................................................................100 B.1.2 General Description...........................................................................101 B.1.3 Horizontal and Vertical Structure.......................................................101 B.1.4 Numerical Procedures.......................................................................101 B.1.5 Boundary Conditions .........................................................................102 B.1.6 Tidal Data Assimilation......................................................................103 B.1.7 Model Applications ............................................................................103
B.3.1 Model Features .................................................................................106 B.3.2 Establishment of the Dredge Log ......................................................107 B.3.3 DREDGE3D Methodology.................................................................107 B.3.4 Analysis of Results ............................................................................108
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Table of Figures Figure 1: Princess Royal Harbour, Oyster Harbour and King George Sound ......................9 Figure 4.1: Typical synoptic evolution during March..........................................................14 Figure 4.2: Typical synoptic evolution during June............................................................15 Figure 6.1: ADCP Mooring configuration ...........................................................................19 Figure 6.2: Location of observation stations used for fixed point verification of winds
(MET), waves (WR) and currents (ADCP and CM). ........................................20 Figure 6.3: Wireless GPS Davis drifter prior to deployment in King George Sound..........22 Figure 6.4: Wireless GPS Davis drifter in King George Sound..........................................22 Figure 6.5: The 10 wireless GPS Davis drifter tracks. .......................................................23 Figure 7.1: Time series of wind direcions during validation period. ...................................27 Figure 7.2: Time series of wind speed during validation period.........................................28 Figure 7.3(a): Monthly wind roses based on Albany airport data..........................................29 Figure 7.3(b): Monthly wind roses based on Mesolaps airport data. ....................................29 Figure 7.4(a): Energetic wind frequency analysis. .................................................................30 Figure 7.4(b): Light wind frequency analysis..........................................................................30 Figure 7.5: Polar wind diagrams based on MesoLAPS for the period March-June for all
years (left) and 2005 (right). ............................................................................31 Figure 8.1: Region over which 3D ocean currents were simulated with GCOM3D. ..........34 Figure 8.2: Example of the ebb tide in KGS and PRH predicted by GCOM3D. ................35 Figure 8.3: Example of the flood tide in KGS and PRH predicted by GCOM3D................35 Figure 8.4: Comparison of near-surface current speeds measured at ADCP4 from
January 21 to February 12, 2006 (blue) with GCOM3D predictions (red). ......36 Figure 8.5: Comparison of near-surface current directions measured at ADCP4 from
January 21 to February 12, 2006 (blue) with GCOM3D predictions (red). ......36 Figure 8.6: Comparison of near-surface current speeds measured at ADCP5 from
February 12 to March 12 (blue) with GCOM3D predictions (red)....................37 Figure 8.7: Comparison of near-surface current directions measured at ADCP5 from
February 12 to March 12, 2006 (blue) with GCOM3D predictions (red)..........37 Figure 8.8: Comparison of near-bed current speeds measured at ADCP4 from January
21 to February 12, 2006 (blue) with GCOM3D predictions (red).....................38 Figure 8.9: Comparison of near-bed current directions measured at ADCP4 from
January 21 to February 12, 2006 (blue) with GCOM3D predictions (red). ......38 Figure 8.10: Comparison of near-surface current speeds measured at ADCP5 from
February 12 to March 12 (blue) with GCOM3D predictions (red)....................39 Figure 8.11: Comparison of near-surface current directions measured at ADCP5 from
February 12 to March 12, 2006 (blue) with GCOM3D predictions (red)..........39
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Figure 8.12: Comparison of near-surface (blue) and near-bottom (red) current speeds
measured at ADCP6 from March 12 to April 29, 2006. ...................................40 Figure 8.13: Comparison of near-surface (blue) and near-bottom (red) current directions
measured at ADCP6 from March 12 to April 29, 2006. ...................................40 Figure 8.14: Comparison of near-surface (blue) and near-bottom (red) current speeds
measured at ADCP5 from March 12 to April 29, 2006. ...................................41 Figure 8.15: Comparison of near-surface (blue) and near-bottom (red) current directions
measured at ADCP5 from March 12 to April 29, 2006. ...................................41 Figure 8.16: Comparison of near-surface (blue) and near-bottom (red) current speeds
measured at ADCP4 from March 12 to April 29, 2006. ...................................42 Figure 8.17: Comparison of near-surface (blue) and near-bottom (red) current directions
measured at ADCP4 from March 12 to April 29, 2006. ...................................42 Figure 8.18: Comparison of the first 5 GPS drifter tracks with the tracks predicted from
GCOM3D near-surface currents (marked with M)...........................................43 Figure 8.19: Comparison of the second 5 GPS drifter tracks with the tracks predicted from
GCOM3D near-surface currents (marked with M)...........................................43 Figure 9.1: Wave model grid regions.................................................................................47 Figure 9.2: Location of MetOcean winter moorings ...........................................................48 Figure 9.3(a): Modelled wave heights at three locations AWAC-1(red), WRB (green) and
ADCP-3 (blue). ................................................................................................49 Figure 9.3(b): Modelled wave directions at WRB...................................................................49 Figure 9.4: Wave height attenuation through KGS. ...........................................................50 Figure 9.5(a): SWAN model (green) versus observed (red) wave heights at WRB. ..............51 Figure 9.5(b): SWAN model (green) versus observed (red) wave heights at AWAC-1. ........51 Figure 9.6: Typical spatial variability of wave induced bottom velocities. ..........................52 Figure 9.7: Time series of wave induced bottom velocities at AWAC-1 (red), WRB
(green) and ADCP-3 (blue)..............................................................................52 Figure 11.1: Plan view of the proposed channel dredging and reclamation in the wharf
and harbour entrance area. .............................................................................58 Figure 11.2: Cross section view of the proposed channel dredging and reclamation in the
wharf and harbour entrance area. ..................................................................59 Figure 11.3: Representation of Princess Royal Harbour Entrance before dredging
showing the model monitoring points inside and outside PRH and in the
entrance (X).....................................................................................................60 Figure 11.4: Representation of Princess Royal Harbour Entrance after dredging...............60 Figure 11.5: The high resolution model study region showing the monitoring points in the
channel and in side and outside PRH. ............................................................61 Figure 11.6: Wind speed in KGS during the 15 days modelled. ............................................62
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Figure 11.7: Wind directions (to) in KGS during the 15 days modelled, showing a variation
from westerlies to north easterlies and back to westerlies. .............................62 Figure 11.8: Sea levels in Princess Royal Harbour before and after dredging....................63 Figure 11.9: Sea levels in the Harbour Entrance before and after dredging. ......................63 Figure 11.10: Sea levels in the shipping channel before and after dredging.........................63 Figure 11.11: Current speeds in Princess Royal Harbour before and after dredging...........64 Figure 11.12: Current speeds in the Harbour Entrance before and after dredging. ..............64 Figure 11.13: Current speeds in the shipping channel before and after dredging.................64 Figure 11.14: Current directions in Princess Royal Harbour before and after dredging. .......65 Figure 11.15: Current directions in the Harbour Entrance before and after dredging............65 Figure 11.16: Current directions in the shipping channel before and after dredging. ............65 Figure 11.17: Numerical “dye” trace 5 days after release from site labelled PRH1 forced by
currents through the channel before dredging is started. ................................66 Figure 11.18: Numerical “dye” trace 5 days after release from site labelled PRH1 forced by
currents through the channel after dredging is completed. .............................66 Figure 11.19: Location of the two spoil ground options. ........................................................68 Figure 11.20: Comparison of current speeds near the surface (blue) and near the bottom
(red) at the outer spoil ground option in September 2005. ..............................69 Figure 11.21: Comparison of current speeds near the bottom (blue) with the wind speed
(red) at the outer spoil ground option in September 2005. ..............................69 Figure 12.1: Sample TSS plot during dredging of the channel by the TSHD showing the
effects of anti-clockwise circulation in KGS during southeasterly winds. ........82 Figure 12.2: Sample TSS plot during dredging of the channel by the TSHD showing the
effects of clockwise circulation in KGS during northeasterly winds. ................82 Figure 12.3: Sample TSS plot during dredging of the channel by the TSHD showing the
effects of circulation in KGS during westerly winds. ........................................83 Figure 12.4: Location of the five stations where time series data were captured during
the analysis of the turbidity results. .................................................................84 Figure 12.5: TSS time series at five locations during dredging starting in March................84 Figure 12.6: TSS time series at five locations during dredging starting in July. ..................85 Figure 12.7: TSS time series at five locations during dredging starting in November. ........85 Figure 12.8: Sea grass mortality zones derived for dredging starting in March...................86 Figure 12.9: Sea grass mortality zones derived for dredging starting in July. .....................87 Figure 12.10: Sea grass mortality zones for dredging starting in November.........................87 Figure 12.11: Sediment accumulation (above 100gm/m2) at the end of the dredging
program which started in March. .....................................................................88 Figure 12.12: Sediment accumulation (above 100gm/m2) 12 months after the start of
dredging in March...........................................................................................88
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Figure 12.13: Sediment accumulation (above 100gm/m2) at the end of the dredging
program which started in July..........................................................................89 Figure 12.14: Sediment accumulation (above 100gm/m2) 12 months after the start of
dredging in July. .............................................................................................89 Figure 12.15: Sediment accumulation (above 100gm/m2) at the end of the dredging
program which started in November................................................................90 Figure 12.16: Sediment accumulation (above 100gm/m2) 12 months after the start of
dredging in November. ...................................................................................90 Figure A.1: Model region showing TSS sites chosen for output in Champion Bay. ...........94 Figure A.2: Sample surface currents from GCOM3D during southerly winds....................95 Figure A.3: Sample surface currents from GCOM3D during north-easterly winds. ...........95 Figure A.4: Satellite photo of the turbid plume on October 30, 2002 .................................97 Figure A.5: Model prediction for the turbid plume on October 30, 2002 ............................97 Figure A.6: Aerial photo of the turbid plume on November 26, 2002 .................................98 Figure A.7: Model prediction for the turbid plume on November 26, 2002.........................98 Figure A.8: Aerial photo of the turbid plume on December 18, 2002 .................................99 Figure A.9: Model prediction on December 18, 2002.........................................................99
Table of Tables
Table 1: Estimate of significant wave heights Offshore and in Princess Royal Harbour....17 Table 2: GEMS ADCP and Drifting Buoy Deployment Locations and MetOcean Wave
and Meteorological stations.............................................................................21 Table 3: SWAN set-up specifications.................................................................................46 Table 4: Extract from the dredge log used to carry out the dredge modelling. ..................72 Table 5: Basic particle size distributions used in the dredge simulations ..........................75 Table 6: Analysed particle settling velocities compared with the values used in the
dredge modelling. ............................................................................................76 Table 7: The Sea grass Impact Zone Criteria Supplied by SKM........................................81 Table A.1: Comparison of Predicted (P1-8) and measured TSS values (TL1-21). ..........96
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1. Introduction
Global Environmental Modelling Systems (GEMS) was contracted to carry out simulations
of the dredging impacts for the development of Albany Port for the Grange Resources
Southdown Magnatite Project. At the time this study was carried out dredging for the port
expansion in Princess Royal Harbour (PRH) and the deepening and extension of the
shipping channel in King George Sound (KGS) was expected to commence sometime in
March 2007 and continue for 4 to 5 months. The study region is shown in Figure 1.
The work has been undertaken using three sophisticated numerical computer models:
The GEMS 3D Coastal Ocean Model (GCOM3D) to simulate the complex three-
dimensional ocean currents in PRH and KGS; and
The GEMS 3D Dredge Simulation Model (DREDGE3D) to determine the fate of particles
released into the water column during the dredging operations; and
The SWAN wave model to simulate the waves in KGS and PRH during the dredging
operations for calculations of sediment re-suspension.
In addition a field program was undertaken to augment existing data and provide an
extensive database for verification of the wind, wave and ocean models.
Figure 1: Princess Royal Harbour, Oyster Harbour and King George Sound
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2. Scope of Work
The Scope of Work for this study has been undertaken as follows:
2.1 Field Work
Deploy wireless GPS ocean surface drifters (Davis drifters) in PRH and KGS to map
surface current movements.
Deploy an Acoustic Doppler Current Profiler (ADCP) at three locations in KGS to measure
currents through the water column.
2.2 Model Setup
Incorporate detailed bathymetry data for PRH and KGS and establish bathymetric grids
covering PRH and KGS for the hydrodynamic, wave and dredge simulation modelling.
Extract data from the high resolution (12km) Bureau of Meteorology forecast model
(Mesoscale Limited Area Prediction System – MesoLAPS).
Analyse the MesoLAPS data for the region to choose a representative dredging period
starting in March.
Setup tidal forcing for the region from the GEMS Australian region tidal database (originally
developed for AMSA Search and Rescue in Canberra).
2.3 Verification of MesoLAPS winds, GCOM3D and SWAN in King George Sound and Princess Royal Harbour
Compare MesoLAPS wind data with observations from the anemometer installed by
MetOcean on a KGS channel pile from July 2005 to April 2006.
Run GCOM3D, driven by tides and MesoLAPS winds, for selected periods and compare
with ocean currents (ADCP and drifter data) and tides measured by MetOcean in winter
2005 and by GEMS in summer 2006.
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Run the SWAN wave model, driven by MesoLAPS winds, and compare wave predictions
with observations from a wave rider buoy installed in KGS from July 2005 to April 2006.
2.4 Simulations for a Representative Dredging Period
• Establish the best estimate of the dredge simulation parameters including:
• Particle distribution curve
• Dredge(s) to be used and proposed hours of operation
• Dredge cutting rate(s)
• All potential sources of turbidity together with rate and duration
• Proposed spoil ground(s)
• Particle size distributions (PSD) encountered along the dredging path
• Establish the expected maintenance schedules and associated down times.
• Develop a detailed dredge log (sample in Table 4) to drive the dredge simulation
program
• Establish the required outcomes of dredge simulations (e.g. TSS levels and
durations, bottom sedimentation thickness, impact zone criteria)
• Run GCOM3D for the representative dredging period driven by winds and tides.
• Run the SWAN wave model for the representative dredging period driven by winds.
• Run DREDGE3D for the full representative dredging period driven by the simulated
dredge log, currents from GCOM3D and orbital velocities from SWAN.
• Analyse output from the simulation to provide data for initial impact assessment
studies.
• Derive impact zones, based on model output and exposure criteria, defining regions
of full mortality, partial mortality and exposure without mortality.
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3. GEMS Background Information GEMS has expertise in the development and application of high-resolution computer
models to realistically predict atmospheric and oceanographic conditions for use in riverine,
coastal and oceanic settings. The GEMS team is made up of qualified and experienced
physical oceanographers, meteorologists, numerical modellers and environmental
scientists.
GEMS is a leading developer of numerical models in Australia. It has developed a system
of validated environmental models that provide solutions to a variety of environmental,
engineering and operational problems. Services provided include:
• Oil Spill Prediction and Risk Modelling under fully representative climatic and
oceanographic conditions;
• Real-time, on-call Oil Spill Modelling
• Dredge sediment fate modelling
• Production Formation Water and Pipeline Hydro-test discharge modelling and
related risk analysis;
• Wave/Current design criteria modelling for pipelines and off-shore and on-shore
facilities;
• Comprehensive tropical cyclone modelling, including winds, waves, currents and
storm surge;
• Provision of accurate tidal prediction based on extensive 2D and 3D
hydrodynamic ocean modelling.
Through it links with Australia’s premier research institution, the Commonwealth Scientific
and Industrial Research Organization (CSIRO), GEMS now includes satellite derived ocean
elevation and large-scale ocean current data into its modelling suite. This state-of-the-art
approach allows more accurate representation of ocean currents to be included in all ocean
discharge applications. The methodology was applied successfully as part of a
comprehensive Environmental Impact Assessment for the Woodside Enfield Project (and
more recently for the BHP Stybarrow and Pyrenees studies) near the Ningaloo Marine
Park.
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4. Climate and Meteorology
The planned operation is to occur during a period (March-June) in which there is marked
change in the predominating synoptic pattern.
At the beginning of the period, in March, the mean position of the sub-tropical ridge is near
its most southern extent in the annual cycle. This ridge of high-pressure routinely directs
easterly quarter winds over the southwest corner of the continent. The pressure gradient
during this period generally shifts more northeasterly on the eastern flank of transitory
eastward propagating heat troughs and then shifts southwards after the passage of the
trough. Usually, a rapidly reforming high will then cause a burst of stronger south-easterlies
following trough passage.
By April, the cooling continent causes the sub-tropical ridge to migrate northwards and the
southwest corner becomes increasingly affected by mid-latitude westerly flow into the
winter months. This increasingly subjects the region to passing frontal and low-pressure
systems; high pressure may still develop over ocean latitudes but tends to be much more
transitory in nature.
Figures 4.1 and Figures 4.2 show examples of the typical evolution of the synoptic pattern
for March and June respectively.
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Figure 4.1: Typical synoptic evolution during March.
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Figure 4.2: Typical synoptic evolution during June
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5 Oceanography
5.1 Circulation The Albany Port is situated in PRH, a marine embayment of surface area 28.7 km2, the
predominant depth being about two metres, with a narrow opening to KGS.
The dominant influence on the circulation in the waters of KGS and PRH is the local wind.
Tides are relatively weak at Albany and vary from diurnal to semi-diurnal throughout the
year with a spring tidal range of approximately 1.1 metres. Water levels are also influenced
by the weather systems, with wind driven setup resulting from sustained winds in KGS
readily transmitted into PRH. The water-level ranges within and outside the harbour are
virtually identical (EPA, 1990).
Modelling of wind driven circulation of water in Princess Royal Harbour (Mills and Brady,
1985) showed that west to north-west winds in Winter generate predominantly anti-
clockwise circulation whereas east to south-east winds in Summer generate predominantly
clockwise circulation. Investigations into water circulation and flushing characteristics of the
Harbour (Mills and D’ Adamo, 1993) also found that up to 30 million m3 of water may enter
or leave the Harbour within 8 hrs of rising tides and 16 hrs of falling tides. The water
movement passing through the entrance channel of the Harbour mouth was found to
accelerate to current speeds of up to 0.5m/sec.
The above findings have been supported by the observations and modelling carried out
during this study and further findings have emerged regarding the circulation in King
George Sound, namely:
• During summer, winds from the south to south-east sector generate a
predominantly anti-clockwise circulation in KGS;
• During summer, winds from the east to north-east sector generate a predominantly
clockwise circulation in KGS;
• During summer, when winds are from the south-east to north-east sector, the
surface flow in the centre of KGS is generally towards the west but the bottom flow
is generally in the opposite direction;
• During winter sustained strong westerly winds generate what appears to be a shelf
wave along the continental shelf outside KGS resulting in current speeds over 1
knot at depths of 40 metres. The amplitude of the bottom current in these situations
correlates well with the wind speed and the phase of the bottom current variations
often leads the phase of the wind.
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5.2 Waves
The broad high latitude westerly flow over Southern and Indian Oceans produces a highly
energetic wave climate at the southwest corner of the continent. However, the
southeasterly to easterly aspect of KGS provides a significant level of protection to these
waves.
While there can be sustained easterly wind flow (see Section 7) in the region, more
particularly in the warmer months, these winds are generally not spatially extensive so that
the resulting waves are less energetic, and at higher frequency.
Occasionally, however, the synoptic pattern may be favourable for the development of
higher energy southeast waves. Typically, these events occur with the development of a
high-pressure system at higher latitudes; such a system may be accompanied by a slow-
moving depression, cut-off from the prevailing westerly flow in the region of the Great
Australian Bight. Strong pressure gradients ‘squeezed’ between such coupled systems
are ideal for generating large southeast waves that propagate towards the study region.
5.2.1 Extreme Wave Analysis
An assessment of the offshore wave climate at Albany was undertaken for Berth No’s 5 and
6 Development, by Lawson and Treloar in 1999. The resulting estimates of significant
wave heights for severe storms offshore and at the entrance to Princess Royal Harbour are
as shown in Table 1.
Table 1: Estimate of significant wave heights Offshore and in Princess Royal Harbour
Recurrence Interval Significant Wave Height (m)
Offshore Entrance to Princess Royal
Harbour
100 years ARI 10.5 m 1.7 m
50 years ARI 9.8 m 1.5 m
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5.2.2 Waves Employed in the Current Study
The primary aim of wave modelling undertaken for the study was to quantify spatial and
time varying wave-induced (bottom) orbital velocities for incorporation into the re-
suspension module of the sediment model.
Although detailed observational wave data have been collected from the study region (see
below), these data are limited because they location specific and because they represent a
small window relative to the overall wave climate.
In order to represent the wave climate for the planned period of operation of the dredger, a
comprehensive wave model (SWAN) has been established. Wave validation studies have
been carried out to assess the accuracy of this model against data collected during the
wave monitoring period. These are discussed in detail in Section 5.2 along with the details
of the model setup and outcomes of the modelling program.
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6. Field Work
In order to produce reliable predictions of the fate of turbid plumes during the dredging it is
critical to have accurate predictions of the ocean currents and tides in PRH and KGS. A
field program measuring winds, waves and currents was undertaken from July to October
2005 by MetOcean. The results of this program were very useful but did not provide
sufficient information to determine the circulation in KGS and given that the dredging
program would start around March 2007 it was decided to pursue further current
measurements in the summer and autumn of 2006.
These field measurements involved:
• The deployment of an Acoustic Doppler Current Profiler (ADCP) at three sites in
KGS by GEMS for approximately 1 month at each location,
• The deployment of five wireless tracked GPS drifting buoys (Davis drifters) for 5
days in PRH and KGS.
6.1 ADCP Deployments
The locations of the fixed point data used for verification in this study are defined in Table 2
and marked in Figure 6.2. The GEMS ADCP mooring components are shown
schematically in the mooring design in Figure 6.1.
Figure 6.1: ADCP Mooring configuration
Buoy
Large small
Current
40m
10m
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The ADCP deployed by GEMS was from RDI Instruments in the USA and was calibrated
and supplied by their agent in Australia (Underwater Video Systems).
The workboat, diving and logistics support for the mooring deployments, was provided by
the Albany Port Authority.
6.2 Drifting Buoy Deployments GEMS developed the wireless tracked GPS drifting buoys (known as Davis drifters)
specifically for lagrangian drifter experiments to help map ocean surface currents (see
figures 6.3 and 6.4). A wireless receiver on the deck of the boat, or mounted on a shore
station, can then receive the location of each of the drifters from the onboard GPS. The
Davis drifters are subject to very low windage due to their design (particularly the
underwater “sail”).
The release points for the wireless GPS Davis drifters are defined in Table 1 and the tracks
are shown in Figure 6.5.
Figure 6.2: Location of observation stations used for fixed point verification of winds
(MET), waves (WR) and currents (ADCP and CM).
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Table 2: GEMS ADCP and Drifting Buoy Deployment Locations and MetOcean Wave and Meteorological stations
Instrument Deployment Latitude
Deployment Longitude
Deployment Time (UTC+8.0)
Retrieval Time (UTC+8.0)
Wave Buoy -35.055560 118.009500 20050403 20060412
Met Station -35.035833 117.930550 20050726 20060412
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10. Dredge Modelling
10.1 Method Once the physical oceanography has been simulated it is possible to study the movement
of discharges into the water column (e.g. sediments, chemicals etc.) or components of the
water body itself (flushing rates of harbours, bays etc.).
The GEMS 3D Dredge Simulation Model (DREDGE3D) is used for simulating the specific
fate of particles discharged during a dredging program. This model inputs the physical
environmental data from GCOM3D, together with wave data from SWAN and
meteorological data, to simulate the movement and deposition, of suspended particles in
the water body across the study area.
DREDGE3D is a lagrangian particle model and therefore is independent of grids and grid
resolutions. More details on the processes and methodology simulated in DREDGE3D is
given in Appendix B.3.
DREDGE3D was used with great success in the Geraldton Port Redevelopment Project
where it was compared with in-situ data, aerial photographs and satellite images.
In the past 3 years since the dredging of Geraldton Port, DREDGE3D has been used in
Mermaid Sound for both the Dampier Port Authority and the Hammersley Iron port
expansion projects, Chevron Gorgon dredging at Barrow Island, two projects in
Queensland, several developments in the United Arab Emirates and in New Caledonia for
the INCO nickel processing plant and port development.
10.2 Verification
The best verification of DREDGE3D available so far was carried out during the Geraldton
Port dredging program. The results are described in Appendix A.
Whilst the Geraldton comparisons provide some important feedback about the accuracy of
DREDGE3D the data was very limited. It is very important to obtain detailed data on TSS
throughout the dredging program to enable much more detailed verification and testing of
the processes simulated in DREDGE3D. It is hoped that these data will be obtained during
this project for comparison with model predictions.
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11. Oceanographic Issues
There have been a number of possible oceanographic impacts of the dredging raised which
need to be considered. In particular, there are two potential issues, which can be
commented on from the modelling work carried out in this study.
11.1 The Effects of Changes to the Entrance to Princess Royal Harbour A significant question for this study therefore is whether the changes to the port
(reclamation and channel deepening) near the entrance to PRH will affect the exchange of
waters between PRH and KGS. The answer is almost certainly yes as the cross-sectional
area of the entrance to PRH is calculated to change from approximately 4,300 m3 to
approximately 5,700 m3 (see Figures 11.1 and 11.2).
11.1.1 Hydrodynamic Studies
The exchange process between PRH and KGS through the existing entrance channel has
been studied previously by Mills and D’Adamo (1993) with a 2 dimensional hydrodynamic
modelling study on a 100 metre grid. In this study the authors conclude that the dominant
mechanisms governing water exchange between PRH and KGS are the wind driven
circulation and asymmetric momentum-driven tidal jets. The modelling work was actually
undertaken in the 1980’s and, as such, was very much state-of-the-science at the time.
The speed of computers twenty years ago limited the resolution at which studies like this
could be carried out and so the 100 metre grid spacing and using a 2D model instead of a
3D model would have been necessary due to the limitations of computational speed. The
limitation of the grid spacing is that the entrance to Princess Royal harbour is less than 200
metres wide at its narrowest point and so there would have been only one water point in the
grid representation of the channel.
Separate studies by CSIRO (McInnes and Hubbert, 1999) have shown that at least five grid
points are required across a channel to represent the flow with any degree of accuracy, and
that seven grid points are preferable. This latter work was carried out during a
hydrodynamic modelling study of the Nerang River at the Gold Coast in Queensland.
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The increase in computational speed, and advances in hydrodynamic modelling
techniques, now allow much higher resolution studies to be undertaken in three
dimensions.
In this study, the effects of increasing the cross-sectional area of the entrance to PRH have
been investigated with a high resolution 3D hydrodynamic model setup to cover PRH, the
entrance channel and the western part of KGS. The model grid resolution was 20 metres
to satisfy the need for at least seven grid points across the entrance channel. The
bathymetry before the dredging is shown in Figure 11.3 and the bathymetry after
completion of dredging is shown in Figure 11.4.
The high resolution model was run over the region shown in Figure 11.5 for 15 days from
July 1 to July 15, 2005 (a full spring - neap tidal cycle) on each of the bathymetric grids
(before and after dredging) to detect any changes in sea levels or currents. The horizontal
resolution was 20 metres and the vertical levels were set at 2, 4,7, 10, 14, 20, 30, 40, etc.
The wind speed and direction derived from the BoM MesoLAPS model for the 15 days are
shown in Figures 11.6 and 11.7 where it can be seen that both easterly and westerly winds
and a range of wind speeds were sampled.
To quantify any changes three monitoring stations were established inside PRH, in the
entrance and outside PRH as shown in Figure 11.5.
The sea levels for the pre- and post-dredging cases, for the spring-neap tidal cycle (15
days), are compared in Figures 11.8, 11.9 and 11.10. These Figures show no changes in
sea level due to the dredging; a result which is not surprising since the tidal water levels in
both PRH and KGS are presently almost exactly the same.
Figures 11.11 – 11.13 compare the current speeds at the three monitoring stations before
and after the dredging for the same 15 day period.
Figure 11.11 shows no change in the current speeds inside PRH whilst Figure 11.12
shows a small decrease in the current speeds through the entrance. This result is
consistent with the fact that the dredging is increasing the cross-sectional area of the
entrance to PRH and so the currents must reduce in speed slightly to maintain a similar flux
to the conditions before dredging.
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Figure 11.13 shows only very small differences in the flow outside PRH, probably due to
the deeper channel.
Figures 11.14 – 11.16 compare the current directions at the three monitoring stations
before and after the dredging for the same 15 day period and show only minor variations in
current directions.
11.1.2 Numerical “Dye” Tracing Studies
A further investigation of the impacts of changes to the entrance channel to PRH was
undertaken through a numerical “dye” tracing study. The 15 days of 3D currents simulated
for the pre- and post-dredging cases were used to drive a model “dye” study where the
numerical equivalent of a neutrally buoyant dye was released throughout the water column
at a strategic location inside PRH channel entrance (see Figure 11.17). The advection and
dispersion of the numerical “dye” was simulated with the GEMS 3D Plume dispersion
model (PLUME3D).
Sample plots of the “dye” trace for the pre- and post-dredging cases after 5 days are shown
in Figures 11.17 and 11.18. In these plots existence of dye at any level in the water column
is shown.
These figures show a minimal difference between the two cases with the dye spreading
slightly more in the post-dredging case, further supporting the belief that the water
exchange between PRH and KGS will be slightly greater after dredging.
After the 15 day simulation, 77% of the dye had left PRH in the post-dredging case
compared with 72% in the pre-dredging case.
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11.1.3 Conclusions from the Hydrodynamic and Numerical “Dye” Tracing Studies
The major conclusions to be drawn from these studies and our understanding of the
oceanography of PRH and KGS are:
• the mass flux through the entrance to PRH due to tidal forces does not change
significantly since the tidal levels are the same in KGS as in PRH;
• the numerical “dye” tracing studies suggest a slightly increased exchange of waters
between PRH and KGS, which will slightly improve flushing but have no impact on
sea levels;
• the exchange of waters between PRH and KGS is not just a two-dimensional
process (i.e. water is not always exchanged as an integrated mass), particularly for
flow produced by winds and not tides;
• Particularly during sustained easterly wind events (northeast to southeast) the
surface waters may flow into PRH but there will be a balancing bottom flow out of
PRH, in the same manner as has been described for KGS during these wind
events.
Figure 11.1: Plan view of the proposed channel dredging and reclamation in the wharf and harbour entrance area.
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Figure 11.2: Cross section view of the proposed channel dredging and reclamation in the wharf and harbour entrance area.
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Figure 11.3: Representation of Princess Royal Harbour Entrance before dredging showing
the model monitoring points inside and outside PRH and in the entrance (X).
Figure 11.4: Representation of Princess Royal Harbour Entrance after dredging.
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Figure 11.5: The high resolution model study region showing the monitoring points in the
channel and in side and outside PRH.
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Figure 11.6: Wind speed in KGS during the 15 days modelled.
Figure 11.7: Wind directions (to) in KGS during the 15 days modelled, showing a variation
from westerlies to north easterlies and back to westerlies.
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Figure 11.8: Sea levels in Princess Royal Harbour before and after dredging.
Figure 11.9: Sea levels in the Harbour Entrance before and after dredging.
Figure 11.10: Sea levels in the shipping channel before and after dredging.
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Figure 11.11: Current speeds in Princess Royal Harbour before and after dredging.
Figure 11.12: Current speeds in the Harbour Entrance before and after dredging.
Figure 11.13: Current speeds in the shipping channel before and after dredging.
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Figure 11.14: Current directions in Princess Royal Harbour before and after dredging.
Figure 11.15: Current directions in the Harbour Entrance before and after dredging.
Figure 11.16: Current directions in the shipping channel before and after dredging.
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Figure 11.17: Numerical “dye” trace 5 days after release from site labelled PRH1 forced by
currents through the channel before dredging is started.
Figure 11.18: Numerical “dye” trace 5 days after release from site labelled PRH1 forced by
currents through the channel after dredging is completed.
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11.2 Waves along the Channel The second issue which can be commented on is the question as to whether the deepening
of the channel in KGS will allow larger waves to penetrate to places such as Middleton
Beach and therefore change the ambient coastal processes.
To test this a wave modelling exercise was carried out with a very high resolution setup of
the SWAN wave model on the pre- and post-construction channel depths. Analysis of the
results of the two wave model runs showed no effect of the channel deepening in KGS and,
in particular, the wave heights off Middleton Beach were unchanged.
11.3 Spoil Ground Location
Originally two spoil ground locations were considered (Figure 11.19) and during the field
program undertaken by MetOcean from July to October 2005 current measurements were
taken at each site to investigate spoil ground stability.
The results at the outer spoil ground were rather surprising as illustrated in Figure 11.20
which shows near bottom current speeds with a similar magnitude to the near surface current
speeds. Moreover the near bottom current speeds reached maxima of approximately 1.5
knots (0.75 m/s). Current speeds of this magnitude at a depth of 36 metres are very unusual
and initially it was thought that the data must be in error. After meeting with MetOcean, who
reanalysed the particular ADCP, it was concluded that these current speeds were real. This
conclusion was further supported by anecdotal evidence from fishermen and divers in Albany
who also reported strong bottom currents in that region.
After plotting the wind speed against the near bottom current speed (Figure 11.21) it became
clear that the cause of the strong bottom currents must be shelf waves generated by the
strong westerly wind conditions during the winter months.
These results indicated that the outer spoil ground location would not be stable and so this
option was not considered any further.
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Figure 11.19: Location of the two spoil ground options.
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Figure 11.20: Comparison of current speeds near the surface (blue) and near the bottom
(red) at the outer spoil ground option in September 2005.
Figure 11.21: Comparison of current speeds near the bottom (blue) with the wind speed
(red) at the outer spoil ground option in September 2005.
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12. Dredging Simulations
The dredge modelling was carried out in two steps. Firstly the 3-dimensional ocean
circulation of the KGS, PRH and Oyster harbour was predicted for 5 months using GCOM3D.
Then the total dredge program was simulated using DREDGE3D, which simulates the
behaviour of the dredge(s) based on an estimated dredge log.
Modelling relied on the best available meteorology and bathymetric information and included
assumptions and details from other recent dredging programs in WA. Where there was
uncertainty in model parameters, conservative values were chosen such that the model
would tend to overestimate the impact.
The dredge modelling was carried out for just over 4 months starting at three distinct times of
the year:
• Starting on March 1, 2005 (dominated by easterly winds);
• Starting on July 1, 2005 (dominated by westerly winds);
• Starting on November 1, 2005 (mixed season with both easterly and westerly winds).
The dredge modelling predicted the hourly distribution of Total Suspended Solids (TSS) and
seabed coverage to be developed over the total dredge program (approximately 120 days).
The hourly output was analysed to derive periods of continuous exposure to turbidity and/or
sedimentation above defined thresholds.
The result of this analysis is summarised in maps of exposure zones showing regions
affected by turbidity or sedimentation that result in high impact, moderate impact or a visible
plume or a very small level of sedimentation.
12.1 Dredge Assumptions The detailed specifications of the dredges and their expected program can be found
elsewhere (JFA, 2006). GEMS worked closely with the dredge management team (JFA) to
define the estimated dredge log, an extract of which is shown in Table 4.
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12.2 Particle Size Distributions and Settling Velocities An important point to note is that all measured settling velocities that we are aware of are
significantly different to theoretical values and so the use of theoretical values as a
benchmark is not valid. Laboratory measurements in Australia are usually performed by the
CSIRO Marine Labs in Perth.
Particle size distributions for this study were defined at every time step from borehole data
taken along the dredging path which was subsequently analysed by the CSIRO Marine Labs.
The particle settling velocities for each particle size in the distribution were also derived by
CSIRO.
The basic particle size distributions for the two main material types (sand and rock flour/clay)
are defined in Table 5. The settling velocities derived by CSIRO for each of these particle
sizes are given in Table 6.
Due to the availability of core data every 100 metres the actual distribution used at each time
step was defined by combining the distributions in Table 5 according to analysed constituent
fractions (i.e fraction of sand plus fraction of clay/rock flour).
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Table 4: Extract from the dredge log used to carry out the dredge modelling. Time