appendix d hydrodynamic and wind wave modelling, and shear

EAW Expansion Project DEIS

D

Appendix D Hydrodynamic and Wind Wave Modelling, and Shear Stress Estimates

Technical Report Darwin Port Expansion EIS

Hydrodynamic and Wind Wave Modelling, and Bed Shear Stress Estimates

16 MARCH 2011

Prepared for

Department of Lands and Planning

5th Floor Energy House 18-20 Cavenagh Street Darwin NT 0800

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Hydrodynamic and Wind Wave Modelling

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Table of Contents

Executive Summary..................................................................................................vi

1 Introduction .......................................................................................................1

1.1 Background ......................................................................................................1

1.2 Project Description...........................................................................................1

2 Hydrodynamic Modelling of Darwin Harbour .................................................2

2.1 ADCIRC model..................................................................................................2

2.2 Model configuration .........................................................................................2

2.3 Model validation ...............................................................................................7

2.3.1 Tidal validations ..........................................................................................................7

2.3.2 Current validations......................................................................................................9

2.4 Modification of currents due to proposed developments ...........................14

3 Wind Wave Modelling .....................................................................................26

3.1 STWAVE model ..............................................................................................26

3.2 Model configuration .......................................................................................26

3.3 Modification of waves due to proposed developments...............................29

4 Bed Shear Stress Estimates...........................................................................39

5 References.......................................................................................................44

6 Limitations.......................................................................................................47

Tables

Table 2-1 Current velocity (m/s) statistics at 8 comparison sites ..................................................25

Table 3-1 Inter-comparison of significant wave height (m) statistics at 8 comparison sites for Hs= 1 m, Tp= 5 s and Hs= 5 m, Tp= 10 s open boundary waves from north, north-west and west; Base case bathymetry........................................................................................30

Table 3-2 Inter-comparison of peak wave period (s) statistics at 8 comparison sites for Hs= 1 m, Tp= 5 s and Hs= 5 m, Tp= 10 s open boundary waves from north, north-west and west; Base case bathymetry.................................................................................................31

Table 3-3 Inter-comparison of wave direction (degree) statistics at 8 comparison sites for Hs= 1 m, Tp= 5 s and Hs= 5 m, Tp= 10 s open boundary waves from north, north-west and west; Base case bathymetry.................................................................................................32

Table 3-4 Inter-comparison of significant wave height (m) statistics at 8 comparison sites for Dredged and Alternative dredged bathymetry; open boundary waves from north, north-west and west .............................................................................................................36


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Table 3-5 Inter-comparison of peak wave period (s) statistics at 8 comparison sites for Dredged and Alternative dredged bathymetry; open boundary waves from north, north-west and west ............................................................................................................................37

Table 3-6 Inter-comparison of wave direction (degree) statistics at 8 comparison sites for Dredged and Alternative dredged bathymetry; open boundary waves from north, north-west and west ............................................................................................................................38

Table 4-1 Inter-comparison of mean bed shear stress (N/m2) estimates at 8 comparison sites; open boundary incident waves from north, north-west and west...................................41

Figures

Figure 2-1 ADCIRC model mesh and colour-coded bathymetry developed for Darwin Harbour.......3

Figure 2-2 Model mesh and colour-coded bathymetry in vicinity of East Arm Port ...........................4

Figure 2-3 January through to June wind roses for the Darwin Airport synoptic station....................5

Figure 2-4 July through to December wind roses for the Darwin Airport synoptic station .................6

Figure 2-5 Location of pressure gauges and ADCPs used in ADCIRC validations...........................7

Figure 2-6 Measured and ADCIRC simulated tidal elevations at four tide gauge sites .....................8

Figure 2-7 Typical ADCIRC simulated ebb currents in Darwin Harbour ...........................................9

Figure 2-8 Typical ADCIRC simulated flood currents in Darwin Harbour .......................................10

Figure 2-9 ADCP measured and ADCIRC modelled currents at Wickham Point site .....................11

Figure 2-10 ADCP measured and ADCIRC modelled currents at Monitor 1 site ..............................11

Figure 2-11 ADCP measured and ADCIRC modelled currents at Monitor 2 site ..............................12

Figure 2-12 ADCP measured and ADCIRC modelled currents at Sentinel 1 site .............................12



Figure 2-15 Concept location and design of proposed developments; after AURECON Drawing No.41840-SK-030 .......................................................................................................14

Figure 2-16 Comparison sites over Walker Shoal and within proposed Dredged and Alternative dredged areas.............................................................................................................15

Figure 2-17 Zoomed-in view of model bathymetry and coastline configuration for Base (top panel), Dredged (middle panel) and Alternative dredged (bottom panel) cases........................16

Figure 2-18 Scatter plots of Base case and Dredged currents at comparison site 1, dry (left panel) and wet (right panel) seasons......................................................................................17

Figure 2-19 Base case and Dredged current velocities at comparison site 1, dry (top panel) and wet (bottom panel) seasons ...............................................................................................17




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Figure 2-24 Scatter plots of Base case and Alternative dredged currents at comparison site 4, dry (left panel) and wet (right panel) seasons ....................................................................20

Figure 2-25 Base Case and Alternative dredged current velocities at comparison site 4, dry (top panel) and wet (bottom panel) seasons .......................................................................20









Figure 3-1 STWAVE model mesh and colour-coded bathymetry developed for Darwin Harbour....27

Figure 3-2 STWAVE nested model mesh and colour-coded bathymetry in vicinity of East Arm Port...................................................................................................................................27

Figure 3-3 Northerly waves (Hs=5 m, Tp= 10 s) propagating through Darwin Harbour (top panel) and in vicinity of East Arm Port (bottom panel).............................................................33

Figure 3-4 North-westerly waves (Hs=5 m, Tp= 10 s) propagating through Darwin Harbour (top panel) and in vicinity of East Arm Port (bottom panel) ..................................................34

Figure 3-5 Westerly waves (Hs=5 m, Tp= 10 s) propagating through Darwin Harbour (top panel) and in vicinity of East Arm Port (bottom panel) ...................................................................35

Figure 4-1 Mean bed shear stress (N/m2) in Darwin Harbour; Base case bathymetry and coastline...................................................................................................................................40

Figure 4-2 Mean bed shear stress (N/m2) in vicinity of East Arm Port; Base case bathymetry and coastline......................................................................................................................40

Figure 4-3 Mean bed shear stress (N/m2) in vicinity of East Arm Port; Dredged case bathymetry and coastline...............................................................................................................42

Figure 4-4 Differences (Base minus Dredged) in mean bed shear stress (N/m2) in vicinity of East Arm Port......................................................................................................................42


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Figure 4-5 Mean bed shear stress (N/m2) in vicinity of East Arm Port; Alternative dredged case bathymetry and coastline.............................................................................................43

Figure 4-6 Differences (Base minus Alternative dredged) in mean bed shear stress (N/m2) in vicinity of East Arm Port ..............................................................................................43


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Abbreviations

Abbreviation Description

ADCIRC-2DDI ADvanced CIRCulation - Two-Dimensional Depth-Integrated model

DLP Department of Lands and Planning

EAW East Arm Wharf

EIS Environmental Impact Statement

Hs Significant wave height

NOI Notice of Intent

NRETAS Natural Resources, Environment and the Arts

NT Northern Territory

STWAVE STeady State spectral WAVE model

TMA TEXEL storm, MARSEN, and ARSLOE spectrum

Tp Peak wave period

URS URS Australia Pty Ltd


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Executive Summary

URS Australia (URS) was commissioned to undertake environmental study associated with Department of Land and Planning preparation of the EIS, and this technical report was prepared in part fulfilment of that commission.

The current study was carried out to develop and validate hydrodynamic and wind wave models plausibly representing ambient current and wave conditions in Darwin Harbour. Data produced by the models were required for modelling sediment discharge and transport within the study area as well as for modelling oil spills. This reports describes the configuration and validation of these models; it also investigates the potential for development dredging and construction works proposed by the DLP within Darwin Harbour to alter a number of existing hydrodynamic processes including water circulation patterns, wave regime and bed shear stress with a specific emphasis on the area around the East Arm Port facilities.

The ADCIRC hydrodynamic model was used for modelling currents based on its flexible mesh capabilities to resolve any features of interest within a model domain, to account for tidal and wind forcing as well as to incorporate wetting and drying of the intertidal mudflats. The model configuration was successfully validated against currents measured in the harbour during both the dry and the wet seasons.

Wave modelling performed using the STWAVE model provided a necessary input to bed shear stress estimates. STWAVE was chosen for this task because it accounts for the important wave generation and dissipation processes in shallow estuarine areas and can flawlessly assimilate tide and currents produced by ADCIRC to account for modification of the waves due to sea level and current velocity and direction variations.

The investigations of the potential current, wave and bed shear stress modifications over both the wider (Darwin Harbour) and more localised (East Arm) scales were conducted through a comparative modelling and subsequent analysis involving the generation of sample currents and wave fields for one pre-construction (present day Base case) and two post-construction (Dredge and Alternative dredge) scenarios. The differences imposed by the proposed developments were further quantified and analysed.

The presented hydrodynamic model results suggest the current velocities and directions would be modified to a different degree at 8 comparison sites within the proposed developments: at some sites, there might be a decrease in current velocities by as much as 45%, while at the others there might be an increase of up to 9%.

The wave modelling results suggest that both short and long waves entering the harbour decay significantly before the waves reach the East Arm Port area, and that both of the proposed developments would lead to wave energy attenuation.

An analysis of the possible change in bed shear stress was conducted to predict the cumulative effect of changes in the tidally driven currents and the wave energy over the entire domain. The mean bed shear stress estimates were calculated for each cell of the model domain over a typical tidal cycle period using the Base case, Dredged and Alternative dredged currents and waves. There would be areas of both decreased and increased bed shear stress around the East Arm Port with the differences ranging from -0.05 N/m2 to +0.05 N/m2. The positive differences imply higher than present day deposition rates/possible sediment accretion, while the negative differences indicate areas of increased re-suspension and erosion rates.


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1

1 Introduction

1.1 Background

The Department of Land and Planning (DLP) is proposing an extension to the East Arm Port, Darwin, Northern Territory (NT).

An EPBC referral was submitted to the Commonwealth Government, which determined that the action is controlled and requires assessment and approval by the Minister for the Environment before it can proceed.

A Notice of Intent (NOI) was submitted to the NT Government to initiate the environmental assessment process for the Project by the NT Environment, Heritage and Arts Division (EHA), under the NT Environmental Assessment Act. The NT Government responded to the NOI in December 2009 with a determination that the action warrants a formal assessment under the Act, at the level of an Environmental Impact Statement (EIS). The NT Draft EIS Guidelines for the Expansion of the East Arm Wharf released by the EHA Division of the NT Department of Natural Resources, Environment and the Arts (NRETAS) presents the requirements for development of the EIS (NRETAS, 2009).

This report was completed to describe the hydrodynamic and wind wave modelling of Darwin Harbour and potential impacts associated with the proposed expansion on water currents, wind waves and bed shear stress in the harbour.

1.2 Project Description

The East Arm Wharf (EAW) is situated on the East Arm Peninsula, within Darwin Harbour. The EAW extends into Darwin Harbour and is bounded by Bleesers Creek to the north and Hudson Creek to the east. The location of EAW is illustrated in Figure 2-1 and Figure 2-2.

The proposed expansion of the East Arm Wharf broadly comprises four separate developments within the East Arm Wharf precinct. The scope of the Draft Environmental Impact Statement (DEIS) includes four main developments and associated works, three of which may affect hydrodynamic and wave regime:

• Defence Hardstand Area • Marine Supply Base • Extension of the existing East Arm Wharf Quay Line.

This report relates to describing the existing conditions in terms of water currents, wind waves and bed shear stress in Darwin Harbour and in the vicinity of the East Arm Port, with qualitative and quantitative impacts associated with the proposed developments.


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2

2 Hydrodynamic Modelling of Darwin Harbour

A hydrodynamic model of Darwin Harbour was developed and applied in this study to properly represent the patterns of water circulation further used in dredging and dredge spoil disposal (i.e. sediment discharge and transport) simulations as well as in oil spill simulations.

2.1 ADCIRC model

The ADCIRC-2DDI (ADvanced CIRCulation - Two-Dimensional Depth-Integrated) model was used in this study to estimate water surface elevations and currents in Darwin Harbour. ADCIRC is a numerical finite element hydrodynamic model specifically developed for applications on shelves, near coasts and in estuaries. The two-dimensional depth-integrated mode of numerical simulations was selected because density gradients in the larger part of the harbour are relatively small, therefore the currents are predominantly barotropic, which is common for estuarine currents driven by macro-tides (e.g. Walters & Cheng, 1979; Wasko et al., 2010).

ADCIRC-2DDI is based on the depth-integrated equations of mass and momentum, ruled by the hydrostatic assumption and the Boussinesq approximation (Westerink et al., 1994). ADCIRC-2DDI is implemented using linear triangular elements for elevation, velocity and depth. The elevation and velocity solutions are computed by the equal order finite element interpolating functions.

The boundary conditions include tidal constituents, wind stress at the water surface and bottom friction. The implemented in the model wetting and drying algorithms allow the simulation of flood inundation and recession near shore and inland elements; this model feature is very important for Darwin Harbour with its large inter-tidal mud flats and mangroves.

During the last 20 years, the model had been extensively tested and applied in different ocean and coastal regions (see e.g. Luettich et al., 1992; Blain, 1998; Fortunato et al., 1998).

2.2 Model configuration

ADCIRC model runs were conducted in the 2DDI (Two-Dimensional Depth-Integrated) mode using an unstructured mesh with 8210 computational nodes (Figure 2-1). The model mesh had 35 open ocean boundary nodes and 1321 land boundary nodes.

The size of the used meshes was variable with coarser meshes used for deeper and outer parts of the model domain and with finer meshes used in more bathymetrically complex inner areas and over the areas of specific interest, e.g. planned dredging channels and pockets (Figure 2-2).

The bathymetric data used for the model development combined several available data sets. High resolution bathymetric maps generated by INPEX for their LNG pipeline and Wickham Point development were combined with the datasets developed by HR Wallingford for their hydrodynamic and wave models (INPEX 2010b) and with the latest IXSurveys data collected in the harbour in the direct vicinity of the East Arm Port in November 2010. The resulting model bathymetry converted into the model mesh can be seen in Figure 2-1 and Figure 2-2.

Tidal forcing applied at the open ocean boundary of the model domain was obtained from the Le Provost tidal database (e.g. Le Provost, 2000; Ponchaut et al., 2001). The tidal data were derived from a dynamical model with assimilation of TOPEX/POSEIDON satellite observations, which started in 1992 (e.g. Lefevre et al., 2002).

Wind data used to define the effects of wind stress on currents were sourced from two independent sources: local observations conducted by APASA at the East Arm Port from April to August 2008, and



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Figure 2-1 ADCIRC model mesh and colour-coded bathymetry developed for Darwin Harbour



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Figure 2-2 Model mesh and colour-coded bathymetry in vicinity of East Arm Port

the Australian Bureau of Meteorology wind observations at the Darwin Airport synoptic station for years 2004-2008 inclusive. Monthly wind roses for this synoptic station are presented in Figure 2-3 and Figure 2-4.

A statistical analysis of the mentioned East Arm Port and Darwin Airport wind observations was carried out in INPEX (2010a); the analysis demonstrated that there was a high correlation (70%-85%) between the observations, which suggests that the winds over the study area are spatially homogenous, and the long-term observations from the Darwin Airport synoptic station can be used for modelling currents in the harbour.

Constant quadratic bottom friction coefficient equal to 0.005 was selected as a result of preliminary model tuning and used in all the further numerical modelling computations.

One of the latest assessments of impact of the wet season freshwater inflow on the current speeds within East Arm was carried out by INPEX (2010a). The assessment demonstrated that the Elizabeth River wet season time-varying flow had some impact in terms of current speed at the upstream extent of East Arm only, where the speed may increase by as much as 0.2 m/s as a result of rain. Any influence would however be hardly traceable by midway along East Arm, and the East Arm Port area would not be affected by such an increase. Therefore, any freshwater inflow from the rivers was disregarded in the modelling as having no effect in the area of interest.



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Figure 2-3 January through to June wind roses for the Darwin Airport synoptic station



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Figure 2-4 July through to December wind roses for the Darwin Airport synoptic station



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2.3 Model validation

The model validation consisted of two separate components: validations of ADCIRC tidal predictions against observations of four tide gauges, and validations of ADCIRC current predictions against observations of six ADCPs. The validation results are described in the two following sections.

2.3.1 Tidal validations

Tidal measurements were performed for the INPEX development project by APASA over the period 14 May-11 June 2008; for locations of the deployed tide gauges see Figure 2-5.

Figure 2-5 Location of pressure gauges and ADCPs used in ADCIRC validations

Inter-comparisons of the modelled and measured tidal elevations at the mentioned locations are presented in Figure 2-6. An analysis of the presented time-series suggests that the ADCIRC model simulated faithfully the magnitude and timing of tidal variations as well as both the spring and the neap tidal phases. This is a clear indication that ADCIRC correctly propagates tidal variations set up at the open boundary through the entire model domain. This in turn provides a reliable basis for consistent hydrodynamic modelling.



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Figure 2-6 Measured and ADCIRC simulated tidal elevations at four tide gauge sites



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2.3.2 Current validations

Typical ebb and flood currents simulated by ARCIRC are presented in Figure 2-7 and Figure 2-8. To ensure that the model plausibly simulates hydrodynamic fields within Darwin Harbour, validations of ADCIRC simulations were conducted against ADCP current records. The ADCPs were deployed by NRETA at the Wickham Point site in February-March 2004 and by APASA at the Monitor 1 and 2 and Sentinel 1, 2 and 3 sites in April-August 2008 (for locations see Figure 2-5), and data from the instruments post-processed by URS to provide consistent with the model, depth-averaged currents. Scatter plots of U- and V-components of the current vectors as well as velocity time series of measured and modelled currents are presented in Figure 2-9 through to Figure 2-14.

Figure 2-7 Typical ADCIRC simulated ebb currents in Darwin Harbour

Comparisons of the observed and simulated currents suggest that the hydrodynamic model provides good estimates of the water flow speed and direction at each of the considered sites located as in the main, wider part of the harbour (such as Sentinel 2 and 3 and Monitor 2) as around the East Arm Port development site and in East Arm (such as Sentinel 1, Wickham Point and Monitor 1).

Both the measured and modelled currents clearly indicate that the prevailing tidally generated water flows in the harbour are steered by the local bathymetric features (see e.g. Figure 2-1). At the Monitor 2 and Sentinel 3 sites, located near the entrance to the harbour, currents flow along the axis of the main entrance channel, which is orientated north-north-west to south-south-east (Figure 2-11 and



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Figure 2-8 Typical ADCIRC simulated flood currents in Darwin Harbour

Figure 2-14). This flow direction is also characteristic of north-west – south-easterly orientated currents in Middle Arm and is well reflected in the measurements and modelling results from the Wickham Point site (Figure 2-9). Currents at the Monitor 1 and Sentinel 1 sites are predominantly running in west-north-westerly and east-south-easterly directions (Figure 2-10 and Figure 2-12) demonstrating that the water flow there is steered by the East Arm channel.

Minor discrepancies between the measured and simulated currents are likely to be due to the typical limitations imposed by e.g. the accuracy of bathymetric data and resolution of the unstructured model mesh, as well as instant nature of field current records and integrated over time model current estimates. The model validations however suggest that the magnitude of the discrepancies would not have any discernable impact on other modelling components’ (e.g. dredging, disposal and oil spill) results.

Note that the Wickham Point current records were collected during the wet season (February-March), while the remainder of the ADCP measurements were carried out over the transition (Monitor 1 and Sentinel 1) and dry season (Monitor 2, Sentinel 2 and 3). The good fit of the measured and modelled currents, simulated using the wind and tide forcing only, suggests that the modelling assumptions were correct, and the density and river inflow effects onto the harbour hydrodynamics are negligible.



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Figure 2-9 ADCP measured and ADCIRC modelled currents at Wickham Point site

Figure 2-10 ADCP measured and ADCIRC modelled currents at Monitor 1 site



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Figure 2-11 ADCP measured and ADCIRC modelled currents at Monitor 2 site

Figure 2-12 ADCP measured and ADCIRC modelled currents at Sentinel 1 site



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2.4 Modification of currents due to proposed developments

Abrupt changes in hydrodynamic patterns may impact both environmental and engineering conditions of an area because currents govern the transport of dissolved substances, including nutrients and pollutants, as well as sediments. The potential for any substance and/or sediment to accumulate in certain areas while being drawn away from others (e.g. erosion and accretion) may affect marine and coastal ecosystem processes, boating and shipping conditions as well as marine and coastal structures.

To estimate effects of dredging and coastal construction developments proposed by DLP, three different hydrodynamic scenarios were set up and modelled for both the dry and the wet seasons:

1) present day bathymetry and coastline configuration (as in e.g. Figure 2-2);

2) dredging of the approach channel to the customs, tug boat and small craft mooring, dredging of the approach channel to the marine supply base and construction of wharf, dredging of the approach channel to and construction of the defence laydown area (as in Figure 2-15);

3) dredging of the approach channel to the customs, tug boat and small craft mooring, dredging of the approach channel to the marine supply base including optional dredging area and construction of alterative wharf, dredging of the approach channel to and construction of the defence laydown area (as in Figure 2-15).

Figure 2-15 Concept location and design of proposed developments; after AURECON Drawing No.41840-SK-030

Eight comparison sites (Figure 2-16) were selected to conduct both qualitative and quantitative evaluations of the variations in current velocity and direction due to the two proposed development options. Hereafter, present day bathymetric and oceanographic parameters will be referred to as Base case, the first of the proposed development options will be referred to as Dredged, while the second, alternative, development option will be referred to as Alternative dredged. For a clear reference, a



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Figure 2-16 Comparison sites over Walker Shoal and within proposed Dredged and Alternative dredged areas

detailed view of the model bathymetry and coastline configuration for each of these three cases is presented in Figure 2-17.

An analysis of the model results obtained over both the dry and wet season months (Figure 2-18 through to Figure 2-33) suggests that at the comparison sites neither current velocities nor current directions differ noticeably between the seasons. The presented scatter plots, time series and calculated statistics (Table 2-1) suggest that, due to the proposed dredging and construction, the current velocities and directions would be modified to a different degree at the sites. For instance, at the comparison sites 1 (Figure 2-18 and Figure 2-19), 4 (Figure 2-24 and Figure 2-25), and 5 (Figure 2-28 and Figure 2-29), both the median (50th percentile) and the maximum current velocities would decrease from 8% to 20% (Table 2-1), while the current direction would noticeably change at the site 4 (Figure 2-24). Dredging of a relative narrow approach channel to the customs, tugs and small craft mooring would reduce the median and the maximum currents by about 0.01 m/s at the sites 2 and 3 (Figure 2-20, Figure 2-21, Figure 2-22, Figure 2-23); the modelling suggests that there would be no change in the current directions. A significant deepening at the comparison site 6 would result in 2-3 fold decrease of both the median and the maximum current velocities (Table 2-1) and about 90o change in the current directions (Figure 2-26 and Figure 2-27). The defence laydown area dredging and construction works would result in a change of the current directions (Figure 2-32) as well as in a decrease in the magnitude of both the median and the maximum current velocities by 42% and 20% respectively (Table 2-1 and Figure 2-33) at the site 8. When combined with the optional dredging and alternative wharf construction, these current velocity statistics for the site 8 would decrease by 45% and 38% respectively (Table 2-1). Note that any decrease in current velocities may lead to variations of sedimentation and accretion rates.

Despite the general decrease, at the site 7 (Figure 2-30 and Figure 2-31) however the current velocities were indicated to increase by 5% to 9% as a result of both the Dredge and Alternative dredge bathymetry modifications (Table 2-1); this may lead to an increase of re-suspension and erosion rates at this location.



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Figure 2-17 Zoomed-in view of model bathymetry and coastline configuration for Base (top panel), Dredged (middle panel) and Alternative dredged (bottom panel) cases



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Figure 2-18 Scatter plots of Base case and Dredged currents at comparison site 1, dry (left panel) and wet (right panel) seasons

Figure 2-19 Base case and Dredged current velocities at comparison site 1, dry (top panel) and wet (bottom panel) seasons



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Figure 2-24 Scatter plots of Base case and Alternative dredged currents at comparison site 4, dry (left panel) and wet (right panel) seasons

Figure 2-25 Base Case and Alternative dredged current velocities at comparison site 4, dry (top panel) and wet (bottom panel) seasons



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Table 2-1 Current velocity (m/s) statistics at 8 comparison sites

Base case Dredged Alternative dredged Station min median max min median max min median max

1 0.00 0.62 1.33 0.00 0.50 1.10 0.00 0.50 1.09 2 0.01 0.13 0.52 0.01 0.13 0.50 0.01 0.13 0.49 3 0.00 0.02 0.08 0.00 0.01 0.07 0.00 0.01 0.07 4 0.00 0.54 1.21 0.02 0.49 1.14 0.01 0.46 1.13 5 0.01 0.47 1.04 0.00 0.38 0.87 0.01 0.46 1.04 6 0.00 0.21 0.60 0.00 0.07 0.18 0.01 0.10 0.27 7 0.01 0.37 0.80 0.01 0.39 0.84 0.01 0.40 0.87 8 0.00 0.33 0.76 0.00 0.19 0.61 0.01 0.18 0.47


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3

3 Wind Wave Modelling

Waves drive sediment transport and nearshore currents, induce wave setup and runup, excite harbor oscillations, or impact coastal structures. In relatively deep water, the wave field is fairly homogeneous on the scale of kilometres; but in the nearshore, wave parameters may vary significantly on the scale of tens of meters. The nearshore wave propagation is influenced by variations in bathymetry, tide-, wind-, and wave generated currents, tide- and surge-induced water level variation, as well as coastal structures. In turn, changes in wave regime and thus wave energy may alter sediment erosion and deposition as well as bed load transport patterns.

3.1 STWAVE model

In the present study, wave propagation simulation analyses have been performed using STWAVE (STeady State spectral WAVE), a model developed by the U.S. Army Corps of Engineers Waterways Experiment Station (Smith et al., 2001). This model was selected from the URS set of models as the most suitable wave model for the purposes of this project. STWAVE is a flexible, robust phase-averaged spectral wave model that has been extensively implemented and verified through research and applied studies around the world (Cialone et al., 2002; Claasen, 2003; Nygaard and Eik, 2004; Kang and Di Iorio, 2006; Smith and Sherlock, 2007; Hanson et al., 2009; Malhadas et al., 2009; Bunya et al., 2010; Rusu, 2011) including Australia (Sanchez et al., 2007; Trinity Point Marina Proposal, 2008). The model has also been used for the U.S Navy operational wave forecasting in the high resolution coastal domains.

STWAVE is a finite difference wave model based on the energy balance formulation for steady-state conservation of wave action along backward-traced wave rays. The model simulates depth-induced wave refraction and shoaling, current-induced refraction and shoaling, depth- and steepness-induced wave breaking, diffraction, wave growth because of wind input, and wave-wave interaction and white capping that redistribute and dissipate energy in a growing wave field. Recent upgrades to the model include wave-current interaction, steepness-induced wave breaking. The updated version also supports either half- or full-plane spectral transformations, spatially varied tidal surge, wind fields and bottom roughness (Smith and Sherlock, 2007). To minimize model computational requirements and maximize accuracy an advanced grid nesting technique has been developed and implemented in STWAVE (Smith and Smith, 2002).

The model accepts two-dimensional spectra as input along with wind speed and direction for inclusion of wind-wave generation. Local wave generation and modification is modelled by using specification of the bathymetry, spatially varying fields of currents and water level elevations. The effect of changing water levels and currents are important input variables for a wave model. Water levels affect both wave breaking and wave refraction due to alteration of water depth. Currents mainly affect the wave refraction but also contribute to wave setup. The model output contains the fields of energy-based, zero-moment wave height, peak spectral wave period, and mean direction; wave spectra at selected locations; and fields of radiation stress gradients.

3.2 Model configuration

STWAVE model was configured to operate on a subset of the ADCIRC domain. The benefit of this approach was that the bathymetry as well as the water elevation and current estimates from ADCIRC could be directly interpolated into STWAVE grids. Advanced grid nesting capabilities of STWAVE were used to create computational grids. A coarse large grid (49.5 km by 29.1 km, Figure 3-1) composed of



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Figure 3-1 STWAVE model mesh and colour-coded bathymetry developed for Darwin Harbour

Figure 3-2 STWAVE nested model mesh and colour-coded bathymetry in vicinity of East Arm Port



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300-metre grid elements was used to transform offshore waves to the boundary of a smaller nested grid (11.37 km by 6.3 km, Figure 3-2) with 30 meter grid elements. To account for the dredging activities in the area, computational grids were developed for three different model bathymetry and coastline configurations (Base case, Dredged, and Alternative) as described in 2.4.

To drive the wave model, a single input spectrum must be specified along the outer boundary of the STWAVE grid. From a review of available wave data for the study area, the source that offered the best definition of the offshore wave conditions were operational wave hindcasts produced by the US National Oceanic and Atmospheric Administration (NOAA) at the National Centre for Environmental Prediction (e.g. Kalnay et al. 1996) using a global wave model WAVEWATCH III. These hindcasts have previously been validated against ocean buoy wind/wave records in many experiments (e. g. Tolman 2002). Wave parameters were extracted from the output of the WAVEWATCH III for the computational point closest to the area of interest (12oS, 130oE) for the period January 1997-July 2009 (NOAA WAVEWATCH III global wave model data ftp://polar.ncep.noaa.gov/pub/history/waves/). It was assumed that the wave conditions at this point are a closes approximation of the wave conditions at the entrance to the harbour.

Darwin Harbour is naturally protected and there is only a limited amount of wave energy entering the harbour from Beagle Gulf. Following the analysis of the frequency of occurrence of wave conditions (see e.g. HR Wallingford 2010) at the mentioned NOAA gridpoint, wave parameters representing both the typical low energy and the infrequently occurring high energy wave situations were selected. Low energy waves with significant wave height (Hs) of 1 m and peak periods (Tp) of 5 s were chosen as the most common in the area. Waves with Hs= 5 m and Tp= 10 s at the open boundary of the domain were selected to represent the most conservative case of high energy wave conditions, which have only 5 occurrences per year (see e.g. HR Wallingford 2010). Three dominant wave directions (north, north-west, west) were considered for the cases of low and high energy waves, thus resulting in 6 model scenarios for this part of the study.

The incident wave spectra were generated from the selected Hs and Tp according to the TMA one-dimensional shallow-water spectral shape (named for the three data sets used to develop the spectrum: TEXEL storm, MARSEN, and ARSLOE; see Smith et al. 2001) and a directional distribution function. Spectral frequency vector ranging linearly from 0.04 to 0.43 Hz with 0.01 Hz increments along with 72 directional bins ranging from 0 to 360 degrees with 5 degree spacing were used in most STWAVE simulations to define both input and calculated spectra over the model grids.

Using the generated spectra at the open boundary, as well as wind, and water levels and currents simulated by ADCIRC, STWAVE was run in half-plane mode to produce wave spectra for each time step over the large grid for a typical two-week neap-spring tidal cycle. These wave simulations for three dominant wave directions at the open boundary were conducted for the three different bathymetry configurations (Base case, Dredged, Alternative dredged), with each simulation consisting of 336 hourly time steps, thus the total of nine model scenarios was formulated for this part of the wave modelling study. Separate STWAVE model runs were then initiated to interpolate the coarse grid spectra onto the nested grid and model the nearshore wave transformation in East Arm for the same number of scenarios and time steps in each model scenario. This approach has the merits of being computationally efficient to set up and to run thus enabling wave propagation strategies to be simulated with maximum accuracy. It also allows to approximate a dynamic simulation by linking STWAVE simulations for all time steps together.

ftp://polar.ncep.noaa.gov/pub/history/waves/



42214000/R001/A 29

3.3 Modification of waves due to proposed developments

In general, wave activity is naturally limited within Darwin Harbour with short period waves propagating into the harbour from Beagle Gulf or locally generated by wind with small significant wave heights of the order of a few tens of centimetres. Circular water particle movements under the short period waves embrace a thin surface layer of water only. These movements rarely penetrate deep enough to “feel the bottom” and thus do not have significant potential to alter sediment erosion and deposition rates in the area. On the other hand, even rare cases of high energy waves propagating into the harbour can cause significant effects within the areas of proposed modifications if the wave energy is not attenuated. A comparison between wave parameters predicted within East Arm for low and high energy waves was conducted to reveal the differences in wave patterns. The statistical wave parameters from the comparison sites (as in Figure 2-16) are shown in Table 3-1 through to Table 3-3.

The presented results suggest that both the short (Tp= 5 s) and the long (Tp= 10 s) wave energies decay essentially before the waves reach the East Arm Port. The median significant wave height of the short and the long waves does not exceed 0.14 m and 0.30 m respectively and the maxima do not exceed 0.31 m and 0.88 m respectively at any of the comparison sites (Table 3-1). Note that, compared to the open boundary condition, the median and the maximum of the peak period of the short waves do not change at any of the comparison sites; this suggests that these waves do not “feel the bottom” and thus would not be affecting erosion and accretion processes taking place in the vicinity of the East Arm Port (Table 3-2).

The median peak period of the long waves coming from the north-west and west decreases at 3 and at 6 of the comparison sites respectively (sites 1-3 and 1-5 and 7, Table 3-2) suggesting that circular water particle motion under these longer period higher waves penetrates through the entire water column at these sites and may affect the erosion and accretion processes.

Following the obtained numerical model results, the short waves were excluded from any further consideration, and modification of the long waves (with Hs of 5 m and Tp of 10 s at the open boundary of the model domain) coming from north, north-west and west were only considered and discussed. Typical wave fields generated by these waves of different incident directions at the open boundary and propagating over the Base case bathymetry are presented in Figure 3-3 through to Figure 3-5.

Table 3-4 through to Table 3-6 give statistics of the significant wave height, peak wave period and wave direction for each of the modelled incident wave directions and Dredged and Alternative dredged bathymetries. A comparison of the long wave Base case statistics from Table 3-1 through to Table 3-3 with the two proposed development statistics (Table 3-4 through to Table 3-6) suggests that the wave parameters at the sites 1, 2 and 3 would not be subjected to any significant modification. The minimum, median and maximum significant wave heights, peak wave periods and wave direction would vary between 0.01 m and 0.06 m, 0 s and 3 s, and 0o and 10o respectively. The dredging and coastline modifications would modify the wave parameters to a larger degree at the rest of the sites, especially after the Alternative dredging and introduction of the Alternative wharf structure, both of which contribute to essential wave energy attenuation, and thus a decrease of wave heights by as much as 0.81 m (for the northerly open boundary waves, the maximum at the site 8), as well as change of wave direction by as much as 28o (for the westerly open boundary waves, the median at the site 4).

Note that any wave energy attenuation may lead to variations of sedimentation and accretion rates.



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Table 3-1 Inter-comparison of significant wave height (m) statistics at 8 comparison sites for Hs= 1 m, Tp= 5 s and Hs= 5 m, Tp= 10 s open boundary waves from north, north-west and west; Base case bathymetry

North Hs= 1 m, Tp= 5 s Hs= 5 m, Tp= 10 s

Station min median max min median max

1 0.06 0.14 0.18 0.18 0.30 0.80

2 0.02 0.10 0.18 0.15 0.24 0.55

3 0.01 0.05 0.08 0.04 0.06 0.10

4 0.03 0.09 0.12 0.07 0.18 0.59

5 0.03 0.08 0.12 0.09 0.18 0.51

6 0.00 0.01 0.03 0.02 0.09 0.35

7 0.01 0.03 0.06 0.07 0.13 0.87

8 0.01 0.02 0.05 0.06 0.12 0.88

North-West Hs= 1 m, Tp= 5 s Hs= 5 m, Tp= 10 s


1 0.09 0.12 0.19 0.17 0.30 0.83

2 0.05 0.09 0.19 0.15 0.24 0.57

3 0.03 0.05 0.09 0.04 0.07 0.13

4 0.04 0.08 0.13 0.08 0.17 0.60

5 0.04 0.07 0.13 0.08 0.17 0.52

6 0.01 0.01 0.03 0.02 0.08 0.34

7 0.02 0.03 0.05 0.06 0.12 0.85

8 0.01 0.02 0.05 0.04 0.11 0.86

West Hs= 1 m, Tp= 5 s Hs= 5 m, Tp= 10 s


1 0.06 0.12 0.28 0.10 0.19 0.66

2 0.04 0.08 0.21 0.09 0.15 0.45

3 0.02 0.03 0.05 0.03 0.05 0.09

4 0.03 0.06 0.23 0.05 0.12 0.54

5 0.03 0.06 0.2 0.05 0.11 0.45

6 0.00 0.01 0.11 0.01 0.05 0.31

7 0.02 0.03 0.31 0.03 0.08 0.81

8 0.01 0.02 0.30 0.03 0.07 0.82



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Table 3-2 Inter-comparison of peak wave period (s) statistics at 8 comparison sites for Hs= 1 m, Tp= 5 s and Hs= 5 m, Tp= 10 s open boundary waves from north, north-west and west; Base case bathymetry



1 5 5 5 7 10 10

2 4 5 5 6 10 10

3 4 5 5 4 7 10

4 4 5 5 5 10 10

5 5 5 5 9 10 10

6 2 5 5 9 10 10

7 2 5 5 7 10 10

8 2 5 5 9 10 10



1 5 5 5 6 7 10

2 5 5 5 5 7 10

3 4 5 5 5 6 10

4 3 5 5 4 10 10

5 3 5 5 6 10 10

6 2 5 5 7 10 10

7 2 5 5 6 10 10

8 2 5 5 6 10 10



1 5 5 5 5 7 10

2 4 5 5 5 7 10

3 3 5 5 4 6 10

4 4 5 5 4 7 10

5 4 5 5 4 7 10

6 5 5 5 7 10 10

7 5 5 5 6 7 10

8 5 5 5 6 10 10



42214000/R001/A 32

Table 3-3 Inter-comparison of wave direction (degree) statistics at 8 comparison sites for Hs= 1 m, Tp= 5 s and Hs= 5 m, Tp= 10 s open boundary waves from north, north-west and west; Base case bathymetry



1 330 333 339 0 334 359

2 340 344 354 0 29 360

3 336 337 339 330 341 348

4 338 341 351 0 15 360

5 341 347 356 1 12 19

6 29 33 51 50 56 65

7 16 22 37 20 37 41

8 24 27 44 25 42 48



1 330 333 345 0 336 360

2 342 344 351 0 35 360

3 337 338 341 329 339 345

4 338 341 348 0 17 360

5 342 346 357 0 10 360

6 28 34 54 47 55 64

7 15 23 41 19 35 39

8 22 28 47 25 40 48



1 1 335 360 0 336 360

2 0 339 360 0 342 360

3 325 332 342 330 339 345

4 0 345 360 0 18 360

5 0 348 360 0 11 360

6 29 46 59 45 55 65

7 16 24 36 19 34 39

8 25 32 45 25 40 48



42214000/R001/A 33

Figure 3-3 Northerly waves (Hs=5 m, Tp= 10 s) propagating through Darwin Harbour (top panel) and in vicinity of East Arm Port (bottom panel)



42214000/R001/A 34

Figure 3-4 North-westerly waves (Hs=5 m, Tp= 10 s) propagating through Darwin Harbour (top panel) and in vicinity of East Arm Port (bottom panel)



42214000/R001/A 35

Figure 3-5 Westerly waves (Hs=5 m, Tp= 10 s) propagating through Darwin Harbour (top panel) and in vicinity of East Arm Port (bottom panel)



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Table 3-4 Inter-comparison of significant wave height (m) statistics at 8 comparison sites for Dredged and Alternative dredged bathymetry; open boundary waves from north, north-west and west

North Dredged Alternative dredged


1 0.16 0.31 0.74 0.15 0.31 0.74

2 0.08 0.23 0.56 0.08 0.23 0.56

3 0.03 0.07 0.13 0.03 0.08 0.14

4 0.09 0.20 0.46 0.08 0.15 0.20

5 0.08 0.17 0.38 0.08 0.15 0.19

6 0.01 0.02 0.07 0.02 0.03 0.04

7 0.06 0.13 0.62 0.06 0.08 0.11

8 0.03 0.09 0.42 0.04 0.05 0.07

North-West Dredged Alternative dredged


1 0.18 0.33 0.80 0.19 0.33 0.80

2 0.09 0.24 0.60 0.09 0.24 0.60

3 0.04 0.08 0.16 0.04 0.10 0.17

4 0.08 0.20 0.48 0.09 0.17 0.22

5 0.09 0.18 0.40 0.10 0.16 0.22

6 0.01 0.02 0.07 0.02 0.02 0.04

7 0.06 0.13 0.61 0.06 0.08 0.12

8 0.03 0.08 0.41 0.03 0.05 0.07

West Dredged Alternative dredged


1 0.11 0.22 0.65 0.12 0.22 0.65

2 0.07 0.15 0.48 0.06 0.15 0.48

3 0.04 0.05 0.11 0.03 0.06 0.10

4 0.05 0.13 0.41 0.07 0.11 0.16

5 0.06 0.12 0.35 0.07 0.11 0.16

6 0.01 0.01 0.07 0.01 0.01 0.04

7 0.04 0.09 0.59 0.03 0.05 0.10

8 0.02 0.05 0.40 0.02 0.03 0.07



42214000/R001/A 37

Table 3-5 Inter-comparison of peak wave period (s) statistics at 8 comparison sites for Dredged and Alternative dredged bathymetry; open boundary waves from north, north-west and west

North Dredged Alternative dredged


1 4 10 10 4 10 10

2 4 10 10 4 10 10

3 4 5 10 4 5 10

4 5 10 10 4 9 10

5 5 10 10 4 6 10

6 9 10 10 9 10 10

7 6 10 10 6 7 10

8 9 10 10 6 10 10

North-West Dredged Alternative dredged


1 5 6 10 5 6 10

2 5 6 10 4 5 10

3 4 5 10 4 5 10

4 5 7 10 4 5 10

5 5 6 10 5 6 10

6 6 10 10 2 10 10

7 6 7 10 6 6 10

8 6 10 10 6 7 10

West Dredged Alternative dredged


1 5 6 10 5 6 10

2 4 6 10 4 6 10

3 4 5 10 4 5 10

4 4 7 10 4 5 10

5 5 6 10 4 5 10

6 2 10 10 2 9 10

7 6 7 10 2 6 10

8 6 9 10 2 6 10



42214000/R001/A 38

Table 3-6 Inter-comparison of wave direction (degree) statistics at 8 comparison sites for Dredged and Alternative dredged bathymetry; open boundary waves from north, north-west and west

North Dredged case Alternative case


1 1 335 360 1 335 360

2 1 35 360 1 35 360

3 326 333 339 326 337 338

4 3 15 28 0 352 360

5 0 6 360 0 354 360

6 40 47 58 45 46 64

7 22 34 41 29 33 41

8 35 47 65 35 42 53

North-West Dredged case Alternative case


1 0 335 360 0 332 338

2 0 335 360 0 346 353

3 326 332 339 325 336 337

4 0 11 360 0 351 360

5 0 5 360 0 355 360

6 40 47 62 44 45 66

7 22 32 41 27 31 38

8 32 46 65 32 40 52

West Dredged case Alternative case


1 0 335 360 0 335 360

2 0 335 360 0 335 360

3 327 332 340 324 332 339

4 0 13 360 0 350 359

5 0 7 360 0 355 360

6 40 47 61 44 45 55

7 22 31 41 28 31 38

8 30 45 65 37 39 46


42214000/R001/A 39

4

4 Bed Shear Stress Estimates

The main hydrodynamic parameter that controls erosion, suspension – re-suspension and deposition of muds and sands in estuaries and coastal waters is bed shear stress, which is the frictional force exerted by the flow per unit area of bed. In many cases, both currents and waves make significant contributions to bed shear stress. Shear stress results from the near-bed current produced by the combined action of the gross hydrodynamic flow acting horizontally and wave induced currents acting orbitally. The wave-induced component of bed shear stress is dependent on bottom orbital motion at the bed, which is characterised by bottom orbital velocity amplitude.

A methodology proposed by Wiberg and Sherwood (2008) was used in this study to calculate orbital velocities from model wave parameters. The accuracy of this approach was confirmed by testing it against field measurements. Using the calculated orbital velocities along with the predicted spatially and temporally changing current and wave fields, bed shear stress estimates were calculated for the Base, Dredged, and Alternative dredged cases following an advanced algorithm of Soulsby and Clarke (2005). Tests of this method against published data gave better agreement than other existing models. A field of the mean bed shear stress estimated over the entire model domain using the modelled currents and long waves is presented in Figure 4-1, with a zoomed-in view of the Base case bed shear stress around the East Arm Port presented in Figure 4-2.

An analysis of the possible change in bed shear stress was conducted to predict the cumulative effect of changes in the tidally driven currents and the wave energy over the entire domain at the same 8 comparison sites (presented in Figure 2-16). To compare the pre- and post- development cases, the mean bed shear stress estimates were calculated for each cell of the model domain over a typical two week tidal cycle period using the Base case, Dredged and Alternative dredged currents and the three previously considered dominant open boundary wave directions, namely, northern, north-western and western waves. Estimates of the mean bed shear stress values at the 8 comparison sites for the period of calculations are presented in Table 4-1.

An analysis of the estimates suggests that bed shear stress would decrease at all of the sites (though insignificantly at some of them e.g. 2, 4, and 8) but the site 7, at which bed shear stress increased due to higher current velocities (see 2.4). A comparison of the means also suggests that the change in wave direction may affect the bed shear stress magnitudes at the sites at the fourth digit after the decimal point only. Therefore, further on, the results for the northern open boundary waves were only considered, mapped and exhibited, including the differences “Base case minus Dredged case” and “Base case minus Alternative dredged case”. An emphasis was made on the area surrounding the East Arm Port with zoomed-in views presented in Figure 4-2 through to Figure 4-6.

An analysis of the plotted results suggest that, due to the proposed dredging and construction, there would be areas of both decreased and increased bed shear stress around the East Arm Port (Figure 4-4 and Figure 4-6). The calculated differences are within the rage from -0.05 N/m2 to +0.05 N/m2. The positive differences would generally imply higher than present day deposition rates and possible sediment accretion, in particular around the proposed coastal structures. The negative differences would indicate areas of increased re-suspension and erosion rates, in particular where the flow conditions were improved and current velocities increased.



42214000/R001/A 40

Figure 4-1 Mean bed shear stress (N/m2) in Darwin Harbour; Base case bathymetry and coastline

Figure 4-2 Mean bed shear stress (N/m2) in vicinity of East Arm Port; Base case bathymetry and

coastline



42214000/R001/A 41

Table 4-1 Inter-comparison of mean bed shear stress (N/m2) estimates at 8 comparison sites; open

boundary incident waves from north, north-west and west

Northern incident waves Station Base case Dredged Alternative dredged

1 0.1325 0.0800 0.0795 2 0.0250 0.0218 0.0217 3 0.0002 0.0000 0.0000 4 0.1109 0.0934 0.1043 5 0.0844 0.0564 0.0831 6 0.0182 0.0023 0.0009 7 0.0579 0.0581 0.0583 8 0.0515 0.0458 0.0355

North-Western incident waves Station Base case Dredged Alternative dredged

1 0.1324 0.0800 0.0795 2 0.0248 0.0217 0.0217 3 0.0002 0.0000 0.0000 4 0.1109 0.0934 0.1043 5 0.0844 0.0564 0.0831 6 0.0182 0.0023 0.0009 7 0.0579 0.0581 0.0583 8 0.0514 0.0457 0.0355

Western incident waves Station Base case Dredged Alternative dredged

1 0.1323 0.0800 0.0795 2 0.0247 0.0217 0.0217 3 0.1419 0.0000 0.0000 4 0.1109 0.0934 0.1043 5 0.0844 0.0564 0.0831 6 0.0182 0.0023 0.0009 7 0.0579 0.0581 0.0583 8 0.0513 0.0457 0.0355



42214000/R001/A 42

Figure 4-3 Mean bed shear stress (N/m2) in vicinity of East Arm Port; Dredged case bathymetry and

coastline

Figure 4-4 Differences (Base minus Dredged) in mean bed shear stress (N/m2) in vicinity of East Arm

Port



42214000/R001/A 43

Figure 4-5 Mean bed shear stress (N/m2) in vicinity of East Arm Port; Alternative dredged case

bathymetry and coastline

Figure 4-6 Differences (Base minus Alternative dredged) in mean bed shear stress (N/m2) in vicinity of

East Arm Port


42214000/R001/A 44

5

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Westerink, J. J., Blain, C. A., Luettich, R. A. Jr. and Scheffner, N. W. (1994). ADCIRC: An Advanced Three-dimensional Circulation Model for Shelves, Coasts, and Estuaries, II: User's Manual for ADCIRC-2DDI. Technical Report DRP-92-6, U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, Mississippi, 156 p.

Wilberg, P. L. and Sherwood, C. R. (2008). Calculating Wave-Generated Bottom Orbital Velocities from Surface-Wave Parameters. Computers & Geosciences, 34, 1243-1262.

Zundel, A. K., Cialone, M. A. and Moreland, T. J. (2002). The SMS Steering Module for coupling waves and currents, 1: ADCIRC and STWAVE. Coastal and Hydraulics Engineering Technical Note CHETN IV-41, US Army Engineer Research and Development Center, Vicksburg, MS.


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6 Limitations

URS Australia Pty Ltd (URS) has prepared this report in accordance with the usual care and thoroughness of the consulting profession for the use of Department of Lands and Planning and only those third parties who have been authorised in writing by URS to rely on the report. It is based on generally accepted practices and standards at the time it was prepared. No other warranty, expressed or implied, is made as to the professional advice included in this report. It is prepared in accordance with the scope of work and for the purpose outlined in the Proposal dated 4 August 2010.

The methodology adopted and sources of information used by URS are outlined in this report. URS has made no independent verification of this information beyond the agreed scope of works and URS assumes no responsibility for any inaccuracies or omissions. No indications were found during our investigations that information contained in this report as provided to URS was false.

This report was prepared between 1 November 2010 and 17 March 2011 and is based on the bathymetric data and coastline configuration obtained from the third party; these data were the most current available at the time of report preparation. URS disclaims responsibility for any changes that may have occurred after this time.

This report should be read in full. No responsibility is accepted for use of any part of this report in any other context or for any other purpose or by third parties. This report does not purport to give legal advice. Legal advice can only be given by qualified legal practitioners.

This report contains information obtained by inspection, sampling, numerical modelling or other means of investigation. The described oceanographic processes and sediment transport in the water environment are complex. Our conclusions are based upon the observed and numerically modelled data presented in this report and our experience. Future advances in regard to the understanding of oceanographic processes and their variability, and changes in regulations affecting their management, could impact on our conclusions and recommendations regarding their potential impacts.

Where conditions encountered at the site are subsequently found to differ significantly from those anticipated in this report, URS must be notified of any such findings and be provided with an opportunity to review the recommendations of this report.

Whilst to the best of our knowledge information contained in this report is accurate at the date of issue, local bathymetry and coastline as well as bed sediment conditions can change in a limited time. Therefore this document and the information contained herein should only be regarded as valid at the time of the investigation unless otherwise explicitly stated in this report.

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appendix d hydrodynamic and wind wave modelling, and shear

Documents