A part of BMT in Energy and Environment Western Basin Dredge Plume Monitoring and Model Validation

Transcription

1 A part of BMT in Energy and Environment Western Basin Dredge Plume Monitoring and Model Validation R.B PlumeMonitoringValidation.doc September 2011

2 Western Basin Dredge Plume Monitoring and Model Validation Prepared For: Prepared By: Gladstone Ports Corporation BMT WBM Pty Ltd (Member of the BMT group of companies) Offices Brisbane Denver Mackay Melbourne Newcastle Perth Sydney Vancouver

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4 CONTENTS I CONTENTS Contents List of Figures List of Tables i ii iii 1 INTRODUCTION D PLUME MODELLING Background TUFLOW-FV Description D Hydrodynamic Model Validation D-3D Plume Simulation Comparison Discussion DREDGE PLUME MONITORING Overview Methodology Field Measurements Data Processing BACK-HOE DREDGE PLUMES General Description Grab Samples Turbidity and TSS Measurements ADCP Transects Background TSS Transects Razende Bol Plume Transects Big Boss Plume Transects Sediment Flux Estimates PLUME MODEL VALIDATION Overview Back-Hoe Dredge SUMMARY 6-1

5 LIST OF FIGURES II 7 REFERENCES 7-1 APPENDIX A: TUFLOW-FV 3D HYDRODYNAMIC VALIDATION A-1 APPENDIX B: BACK-HOE DREDGE MONITORING B-1 APPENDIX C: BACK-HOE DREDGE MODEL VALIDATION C-1 LIST OF FIGURES Figure 2-1 ADCP Locations 2-4 Figure 2-2 3D Model Velocity Profile Comparison with ADCP Data 2-5 Figure 2-3 Figure 2-4 Figure 2-5 Figure 2-6 2D Model Depth-Averaged Plume TSS Concentration Exceeded 50% of the Time 2-6 3D Model Depth-Averaged Plume TSS Concentration Exceeded 50% of the Time 2-6 2D Model Depth-Averaged Plume TSS Concentration Exceeded 10% of the Time 2-7 3D Model Depth-Averaged Plume TSS Concentration Exceeded 10% of the Time 2-7 Figure 4-1 Location Plan 4-2 Figure 4-2 The Razende Bol in Operation 4-3 Figure 4-3 Water Level at Fisherman s Landing 4-3 Figure 4-4 Wind at Gladstone Airport 4-4 Figure 4-5 Grab Sample from Adjacent to Big Boss 4-4 Figure 4-6 Grab Sample from Adjacent to Razende Bol 4-5 Figure 4-7 Figure 4-8 Figure 4-9 Figure 4-10 Turbidity Profiles whilst Monitoring the Razende Bol on a Flooding Tide 4-6 Turbidity Profiles whilst Monitoring the Razende Bol on an Ebbing Tide 4-7 Turbidity Profiles whilst Monitoring the Big Boss on a Flooding Tide 4-7 Turbidity Profiles whilst Monitoring the Big Boss on an Ebbing Tide 4-8 Figure 4-11 TSS-Turbidity Relationship 4-8 Figure 4-12 Depth-Averaged TSS for All Transects 4-9 Figure 4-13 Ebb-Tide Transect Up-Current from Razende Bol 4-10 Figure 4-14 Flood-Tide Transect Up-Current from Razende Bol 4-10 Figure 4-15 Razende Bol Flood Tide Plume Cross-Section (near-field) 4-11 Figure 4-16 Razende Bol Flood Tide Plume Long-Section 4-12 Figure 4-17 Razende Bol Flood Tide Plume Cross-section (far-field) 4-12

6 LIST OF TABLES III Figure 4-18 Big Boss Flood Tide Plume Section (near-field) 4-13 Figure 4-19 Big Boss Flood Tide Plume Section (far-field) 4-14 Figure 5-1 Measured Plume Only TSS - All ADCP Transects (13/07-14/07) 5-3 Figure 5-2 Modelled Maximum Plume Only TSS (13/07-14/07) 5-3 Figure 5-3 Figure 5-4 Figure 5-5 Razende Bol Model vs ADCP Plume Only TSS Comparison (near-field) 5-4 Razende Bol Model vs ADCP Plume Only TSS Comparison (mid-field) 5-4 Razende Bol Model vs ADCP Plume Only TSS Comparison (long-section) 5-5 Figure 5-6 Big Boss Model vs ADCP Plume Only TSS Comparison (near-field) 5-5 Figure 5-7 Big Boss Model vs ADCP Plume Only TSS Comparison (mid-field) 5-6 LIST OF TABLES Table 4-1 Water Sample TSS-Turbidity Data 4-6 Table 4-2 Suspended Plume Sediment Flux Estimates 4-15 Table 5-1 Dredge Plume Model Sediment Fractions and Settling Parameters 5-1

7 INTRODUCTION INTRODUCTION Gladstone Ports Corporation are undertaking the Western Basin port expansion project in order to accommodate the incipient Liquid Natural Gas (LNG) industry. The project will involve capital dredging of 15 Mm 3 of material from Port Curtis in order to develop new navigable channels and swing basins to the east of the Passage Islands/Shoals and to expand the existing Targinie Channel and Clinton Bypass Channel. Material from the dredging will be predominantly placed in the new Western Basin reclamation, which expands to the north the existing Fisherman s Landing reclamation. Some material from the capital dredging works will also be placed at the existing offshore Dredge Material Placement Area (DMPA) situated outside Port Curtis. BMT WBM Pty Ltd has previously undertaken numerical modelling of dredge plumes in order to inform the Western Basin Dredging Environmental Impact Statement (EIS) and Dredge Management Plan (DMP) processes. A particular requirement of the Western Basin DMP is targeted monitoring of the plumes generated by dredge operations, along with comparison of the monitoring data with output from the plume model in order to perform a model validation. A number of different types of dredging plant will be used during the Western Basin project, including; Back-hoe dredges filling hopper barges for DMPA disposal; Cutter Suction Dredge (CSD) pumping into the Western Basin reclamation; and Trailer Suction Hopper Dredge (TSHD). As of the end of August 2011, only the Back-hoe dredge operations had commenced works in the Western Basin. This report details the targeted field monitoring undertaken for the back-hoe dredges, the Razenda Bol and the Big Boss during standard operations on the 13 th and 14 th July Dredge plume monitoring methodology is presented in Section 3, the processed data is presented in Section 4 and plume model validation in Section 5. The Port Curtis numerical hydrodynamic and plume simulation model established by BMT WBM and used in the Western Basin Environmental Impact Statement (EIS) and Dredge Management Plan (DMP) has been continually refined and validated against an extensive compilation of field data as detailed in BMT WBM (2011b). Recently the model has been extended from a 2D depth-averaged configuration to 3D. Section 2 of this report compares 3D plume simulations with 2D simulations undertaken for the Western Basin DMP.

8 3D PLUME MODELLING D PLUME MODELLING 2.1 Background This section of the report compares 3D numerical model plume simulations with 2D depth-averaged model results, in order to provide a clearer understanding of the importance of three-dimensionality in describing hydrodynamic and plume dispersion processes within Port Curtis. Previous plume modelling undertaken for the Western Basin EIS (GHD, 2009) and DMP (Aurecon, 2011) has made use of a numerical hydrodynamic and plume dispersion model of Port Curtis that is 2D depth-averaged. The depth-averaged approximation was considered to be appropriate for simulating hydrodynamic and plume-dispersion processes in Port Curtis based on the following reasons. Port Curtis experiences a macro-tidal regime with spring tidal ranges commonly exceeding 3m. This large tidal range and associated tidal prism induces high tidal current speeds in the channels as well as wetting/drying of extensive inter-tidal areas. These processes are responsible for ensuring that the waters of Port Curtis are generally both vertically and horizontally well-mixed. Temperature and salinity profiles collected across 3 separate transects during the late June 2009 spring tides (refer BMT WBM 2011b) were generally vertically uniform and indicate an absence of stratification. Profiles collected at the same 3 transects during neap tides in late April also generally show only small variations of temperature and salinity with depth. The well-mixed and predominantly 2D nature of Port Curtis hydrodynamic processes is also supported by numerical modelling undertaken by CSIRO as part of the Coastal CRC CM2 Project (CSIRO, 2003). Continuous velocity profile datasets obtained by 3 bottom-mounted Acoustic Doppler Current Profiler s deployed by GHD during May/June 2009 were inspected in order to assess threedimensionality of the flow in the main channels (refer BMT WBM 2011b). The velocity magnitude and direction profiles were plotted at 3-hourly intervals for a spring tide cycle, neap tide cycle and a tidal cycle during strong south-easterly winds. The current magnitude measurements are indicative of the logarithmic current profile that would be expected in a fully-mixed boundary layer. Current directions are generally uniform across the full-depth, with some greater variation seen around the turn of the tide, particularly during strong wind conditions. These measurements support the use of a 2D-depthaveraged model for representing the hydrodynamics of Port Curtis under typical tidal and wind-driven conditions. 2.2 TUFLOW-FV Description TUFLOW-FV is a flexible mesh hydrodynamic model that solves the Non-Linear-Shallow-Water- Equations (NLSWE) including scalar transport in either a 2D-depth-averaged or 3D configuration. TUFLOW-FV has the capacity to include meteorological forcing, wave related stresses and sediment transport (refer BMT WBM, 2011b for further details).

9 3D PLUME MODELLING 2-2 The TUFLOW-FV model of Port Curtis covers the whole tidal waterway network of Port Curtis from south of Facing Island through the Narrows to Keppel Bay including all connected rivers and creeks (see BMT WBM, 2011b). The variable spatial resolution capability of TUFLOW-FV is particularly appropriate for the Port of Gladstone model given the large area of coverage where the resolution of far field areas may be reduced while still allowing the necessary detail to represent channels and berth pockets in areas of interest. The TUFLOW-FV 3D model configuration for Port Curtis used a Z-layer vertical discretisation with 16 layers of height 1m at the surface increasing to 2.5m below 12.5m AHD. Identical plan-view meshes were used for both the 2D and 3D model, with the 2D model having cells and the 3D model having cells. The 2D and 3D TUFLOW-FV model configurations are identical except for the following differences: 3D model has multiple vertical layers; Unlike the 2D model, the 3D model explicitly resolves plume dispersion due to vertically nonuniform current speed. Therefore, while the 2D model uses an Elder type dispersion model to simulate this process (refer BMT WBM, 2011b) the 3D model uses much lower dispersion coefficients calculated using a Smagorinsky model; and The 3D model requires additional parameterisation of vertical mixing. A zero-equation parametric turbulence model has been used D Hydrodynamic Model Validation The 2D TUFLOW-FV hydrodynamic model of Port Curtis has been extensively validated against multiple datasets collected over the period (BMT WBM, 2011b). The 3D hydrodynamic model configuration was validated against Acoustic Doppler Current Profiler (ADCP) data collected as part of the Western Basin EIS project. Continuous timeseries of current profile data were measured during May/June 2009 at the three locations shown in Figure 2-1 by bottom-mounted ADCP instruments. Previous inspection of this data had confirmed that the vertical current profiles measured in Port Curtis channels are consistent with a well-mixed, macro-tidal estuary. Other than at the turn of the tide, the velocity profiles exhibit consistent uni-directionality and a typical logarithmic-profile current speed distribution expected of a fully-developed turbulent and gradually-varied flow field. At the turn of the tide subtle tidal-phasing differences between the surface and bottom currents become apparent. The 2D and 3D model configurations are compared with the ADCP data in Appendix A. Both 2D and depth-averaged 3D results show good agreement with the data and are close to being indistinguishable from each other. An ADCP vertical profile is compared with the 3D model predictions in Figure 2-2 below. The model is reproducing the logarithmic and uni-directional vertical profile that was typical of the ADCP measurements.

10 3D PLUME MODELLING D-3D Plume Simulation Comparison The potential differences between 2D and 3D plume simulations have been investigated by undertaking a combined plume scenario simulation with both model configurations. The 2D and 3D results are compared below for the depth-averaged TSS concentrations exceeded 50% and 10% of the time during the simulation as illustrated in Figure 2-3 to Figure 2-6. The plume source terms were input into the 3D model with a vertically-uniform distribution in order to be consistent with the 2D model. However, the 3D model also has the ability to accept non-uniform vertical source term distributions. 2.5 Discussion The 2D and 3D modelled plume extents are generally similar. In general the 2D model is predicting slightly larger maximum plume extents than the 3D model. There are two reasons why this may be the case. Firstly, the 2D and 3D configurations are using different dispersion models, with the 2D model generally using higher diffusivities to account for the non-uniform velocity profile dispersion that is not resolved explicitly. Secondly, the 3D model explicitly resolves vertical current and sediment profiles. In general the current speeds reduce towards the bed while the sediment concentrations increase towards the bed. This combination generally results in slightly less advection of the sediment plumes in the 3D model than in the 2D model. It can be concluded from the analysis performed here that the 2D plume modelling predictions undertaken for the Western Basin EIS and DMP are consistent with the predictions that would arise from a more detailed 3D model. As discussed above this result is expected given the macro-tidal and well-mixed nature of the hydrodynamic processes within Port Curtis. Unlike a 2D model, a 3D model is able to explicitly resolve vertical variations in currents and plume concentrations, and in cases where these are substantially non-uniform, the 3D model will generally have better predictive skill than a 2D depth-average model. In some instances the additional information regarding vertical distributions which is available from the 3D model may be of use in quantifying impacts.

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12 3D PLUME MODELLING 2-5 Figure 2-2 3D Model Velocity Profile Comparison with ADCP Data

13 3D PLUME MODELLING 2-6 Figure 2-3 2D Model Depth-Averaged Plume TSS Concentration Exceeded 50% of the Time Figure 2-4 3D Model Depth-Averaged Plume TSS Concentration Exceeded 50% of the Time

14 3D PLUME MODELLING 2-7 Figure 2-5 2D Model Depth-Averaged Plume TSS Concentration Exceeded 10% of the Time Figure 2-6 3D Model Depth-Averaged Plume TSS Concentration Exceeded 10% of the Time

15 DREDGE PLUME MONITORING DREDGE PLUME MONITORING 3.1 Overview As part of the Western Basin project DMP, GPC have undertaken to perform direct monitoring of the dredge plumes for the purpose of verifying the numerical model predictions made during the EIS and DMP phases. The monitoring described in this report is distinct from, and in addition to, the continuous real-time sensitive receptor monitoring commissioned by GPC as part of the Western Basin project. The dredge plume monitoring described in this report was targeted at obtaining suitable datasets for the purpose of numerical plume model validation. The equipment used, the field monitoring techniques employed, and the subsequent data processing and analysis have been designed to derive information of relevance to numerical plume modelling such as: Plume source rates; and Plume material settling and dispersion characteristics. The measurements obtained also provide a means of directly testing and validating the numerical plume model predictive skill. 3.2 Methodology Field Measurements All field measurements were conducted from a BMT WBM crewed vessel operating in the vicinity of the dredge operations. The following field sampling instrumentation and techniques were employed during the course of the dredge plume monitoring: Drogue deployments where applicable to guide the location of ADCP transects and to provide a visible surface indicator of the turbid plume paths; Vessel mounted Acoustic Doppler Current Profiler (ADCP) to record changes in the concentration of particles through the water column by measuring acoustic backscatter intensity. Characterisation of the dredging plumes were generally constructed by undertaking consecutive transects through the plumes formed during dredging; Calibrated turbidity measuring instrument to measure water turbidity within and external to the dredge plumes. Collecting many turbidity profiles for use in the conversion of ADCP backscatter intensities to suspended solids concentrations and for additional assessment of the sediment plumes; Water sampling at various depths and over a wide range of Total Suspended Solids (TSS) concentrations for use in the calibration of the ADCP backscatter intensities and assessment of the sediment plumes; Bed material grab sampling in order to qualitatively characterise the material being dredged.

16 DREDGE PLUME MONITORING Data Processing Suitably processed ADCP measurements were used to remotely measure the suspended load in the water column with a sufficient resolution to provide pictorial views of the suspended load associated with dredging and material placement plumes. ADCP measurements can be used to estimate suspended sediment concentration profiles in the water column, however an ADCP instrument does not directly measure TSS. The principle of ADCP operation is that a pulse of sound is propagated through the water column and is backscattered off material in the water column (such as suspended sediment). The Doppler shift of the backscattered acoustic signal is used to directly determine the current profile. The intensity of the backscattered echo can be used along with supporting measurements to estimate the suspended sediment concentration profile. Water quality measurements were conducted concurrently with the ADCP profiling using a handheld multi-probe meter and water samples were taken for subsequent laboratory analysis. The measurements of turbidity in Nephelometric Turbidity Units (NTU) were plotted against Total Suspended Solids (TSS) measurements from the laboratory samples to determine the site and date specific NTU-TSS relationship. The TSS estimates obtained both directly from lab samples and indirectly from turbidity measurements were then used to derive a relationship between the ADCP acoustic signal backscatter intensity and TSS. The software package Sediview includes a built-in calibration module for this purpose which is based on acoustic theory. The calibration process requires information on water temperature and salinity at the site, scaling factors and offsets for each of the four transducers in the ADCP instrument, the sediment attenuation coefficient (a function of the sediment characteristics) and other calibration constants. The estimates of TSS obtained from the ADCP backscatter signal were typically plotted as a function of depth and distance along each transect. TSS estimates were capped at a maximum value approximately set by the calibration dataset due to the uncertainty surrounding the accuracy of the calibration procedures above that level and in order to alleviate the problem of erroneous backscatter spikes in the ADCP measurements. It should also be noted that due to its mounting and a measurement blank-distance the ADCP is only able to resolve TSS profiles below a depth of approximately 1.5m. ADCP backscatter measurements are prone to occasional spikes/elevated values that are un-related to TSS in the water column. These spikes may arise due to a number of sources of interference, including bubbles generated near the surface by the survey vessel / dredge / 3 rd -party vessel and objects pinged in the water-column such as fish or seaweed. The data presented in this report has not been cleaned other than the TSS cap mentioned above. The depth averaged sediment flux vector was estimated by multiplying the above-background TSS concentration at each elevation in each profile by the corresponding water velocity vector and then taking the depth average.

17 BACK-HOE DREDGE PLUMES BACK-HOE DREDGE PLUMES 4.1 General Description Monitoring of back-hoe dredge plumes was undertaken on the 13 th and 14 th of July Two Backhoe dredges, the "Razende Bol and the Big Boss were operating at the locations shown in Figure 4-1. The tide variations during the measurement period are shown in Figure 4-3. The measurement window fell approximately midway between neap and spring tide periods, with high to low tide ranges of between 2.5 and 3.5m experienced. Measurements were conducted during both the morning ebb tide and afternoon flood tide conditions. The prevailing wind conditions during the measurements were calm to light breezes. Both of the back-hoe dredges were operating in relatively shallow water depths outside of the main channels. Visible turbid plumes were distinguishable in the vicinity of both dredges. A less distinct sediment re-suspension plume could be observed originating more generally from the shallow banks in the vicinity of both dredges. The dredge plumes typically became indistinguishable from background turbidity conditions once the plume had been advected out of shallow water and been mixed with the main channel flow.

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19 BACK-HOE DREDGE PLUMES 4-3 Figure 4-2 The Razende Bol in Operation Fishermans Landing 3 2 Water Level (m AHD) /07 08/07 09/07 10/07 11/07 12/07 13/07 14/07 15/07 16/07 17/07 18/07 19/07 20/07 21/07 22/07 Recorded Figure 4-3 Water Level at Fisherman s Landing Gladstone Radar Wind Speed (m/s) /07 08/07 09/07 10/07 11/07 12/07 13/07 14/07 15/07 16/07 17/07 18/07 19/07 20/07 21/07 22/07 Recorded

20 BACK-HOE DREDGE PLUMES Gladstone Radar 315 Wind Direction (Degrees true) /07 08/07 09/07 10/07 11/07 12/07 13/07 14/07 15/07 16/07 17/07 18/07 19/07 20/07 21/07 22/07 Recorded Figure 4-4 Wind at Gladstone Airport 4.2 Grab Samples Surficial sediment grab samples were taken adjacent to both the Big Boss and the Razende Bol. The Big Boss was operating in the Passage Island Channel adjacent to the western shoreline of Curtis Island in water depths of around 1-2m (LAT datum). The in-situ surficial sediment in the vicinity of the Big Boss was qualitatively categorised as sandy mud with some organic matter as shown in Figure 4-5. The Razende Bol was operating to the north of North Passage Island in water depths of around 1-2m (LAT datum). The in-situ surficial sediment in the vicinity of the Razende Bol was qualitatively categorised as dark grey sand with shell fragments as shown in Figure 4-6. Figure 4-5 Grab Sample from Adjacent to Big Boss

21 BACK-HOE DREDGE PLUMES 4-5 Figure 4-6 Grab Sample from Adjacent to Razende Bol 4.3 Turbidity and TSS Measurements A total of 26 turbidity measurement profiles were undertaken concurrently with the ADCP dredge plume measurements. The measured turbidity profiles are shown in Figure 4-7 to Figure 4-10 below. The maximum turbidity measured in the dredge plume adjacent to the Big Boss was 70 NTU. The maximum turbidity measured in the dredge plume adjacent to the Razende Bol was 40 NTU. During the 2 day monitoring period the background turbidity level measured remote from the dredge plumes typically ranged between 5-10 NTU. Significant variations in background (not dredge plume) turbidity levels were observed depending on both the location and timing of the measurement with respect to the tide. Background turbidity was higher along the western shoreline of Curtis Island (in the vicinity of the Big Boss) than it was in the vicinity of the Passage Islands. This is probably in part due to the greater fines content in the surface bed sediment in this area. A total of 15 water samples were obtained and analysed for TSS concentrations. The precise time and location of these samples was recorded in order that they could be accurately correlated with a concurrent turbidity recording from the profiling measurements described above. The TSS-turbidity dataset obtained during the back-hoe dredge plume monitoring is summarised in Table 4-1 and the TSS-turbidity relationship is plotted in Figure This relationship was used to convert the turbidity profile measurements into an equivalent TSS value. A composite dataset of TSS measurements was prepared from the two sources described above, and was subsequently used in calibrating the ADCP backscatter to TSS conversion. The Sediview software package was used to assist with the calibration and conversion of the raw ADCP measurements into estimated TSS profiles. A single best-fit set of conversion parameters was determined through a calibration process, with the quality of the calibration shown in various diagnostic plots in Figure A-2 for measurements on day 1, and Figure A-3 for measurements on day 2. The quality of the Sediview calibration is considered to be acceptable, and the ADCP derived TSS estimates are therefore considered to be generally reliable.

22 BACK-HOE DREDGE PLUMES 4-6 Table 4-1 Water Sample TSS-Turbidity Data SAMPLE TSS (mg/l) Turbidity (NTU) P P P P P P P P P P P P P P P Figure 4-7 Turbidity Profiles whilst Monitoring the Razende Bol on a Flooding Tide

23 BACK-HOE DREDGE PLUMES 4-7 Figure 4-8 Turbidity Profiles whilst Monitoring the Razende Bol on an Ebbing Tide Figure 4-9 Turbidity Profiles whilst Monitoring the Big Boss on a Flooding Tide

24 BACK-HOE DREDGE PLUMES 4-8 Figure 4-10 Turbidity Profiles whilst Monitoring the Big Boss on an Ebbing Tide Figure 4-11 TSS-Turbidity Relationship

25 BACK-HOE DREDGE PLUMES ADCP Transects The entire set of processed ADCP measurements of TSS profiles are shown individually in Appendix A. Figure 4-12 below shows a plan view of depth-averaged TSS for all ADCP transects from the back-hoe dredge monitoring. Higher TSS levels are seen in the vicinity of both the Razende Bol and the Big Boss. Background TSS levels are seen to be higher in the Passage Island Channel adjacent to the Big Boss than in the Targinie Channel (North) adjacent to the Razende Bol. TSS concentrations are typically higher on the shallow banks than in the deeper channels. Figure 4-12 Depth-Averaged TSS for All Transects Some individual ADCP transects are shown in the figures below, in terms of depth-averaged TSS in the top image, and cross-sectional profile in the bottom image. It should be noted that the ADCP measurements have a blank distance of approximately 1.5m from water surface Background TSS Transects Figure 4-13 shows an ebb-tide transect taken up-current from the Razende Bol. It shows relatively uniform and low TSS concentrations of around 5 mg/l. Figure 4-14 shows a flood-tide transect taken up-current from the Razende Bol. It shows the presence of a sediment re-suspension plume being generated from the shallow banks adjacent to North Passage Island. This plume is not directly generated by the dredging activities.

26 BACK-HOE DREDGE PLUMES 4-10 Figure 4-13 Ebb-Tide Transect Up-Current from Razende Bol Figure 4-14 Flood-Tide Transect Up-Current from Razende Bol Razende Bol Plume Transects Figure 4-15 is a cross-section through the plume generated by the Razende Bol and advected around 100m to the north on a flooding tide. The lateral mixing of the dredge and re-suspension plumes from the shallow banks into the main channel can be seen. The main dredge plume width is of the order m.

27 BACK-HOE DREDGE PLUMES 4-11 Figure 4-16 is a long-section through the plume generated by the Razende Bol on a flooding tide. The plume was generally indiscernible from the background levels from around m downcurrent from the dredge. Figure 4-17 is a 350m wide cross-section taken around 500m directly down-current from the Razende Bol on a flooding tide. At this distance from the source the dredge plume was indistinguishable from the background levels generated by the mixing of the bank re-suspension plume with the less turbid water in the channel. Figure 4-15 Razende Bol Flood Tide Plume Cross-Section (near-field)

28 BACK-HOE DREDGE PLUMES 4-12 Figure 4-16 Razende Bol Flood Tide Plume Long-Section Figure 4-17 Razende Bol Flood Tide Plume Cross-section (far-field) Big Boss Plume Transects Figure 4-18 is a transect that provides a near-field cross-section through the plume generated by the Big Boss on a flooding tide. At this proximity to the dredge (~50m) the plume width is also around 50m. The transect started up-current from the dredge and then looped around through the main channel and back into the bank just down-current from the dredge. The cross-section shows the

29 BACK-HOE DREDGE PLUMES 4-13 sharp transition from background TSS levels to the plume which is localised along the edge of the bank. Figure 4-19 shows a cross-section taken around 400m directly down-current from the Big Boss on a flooding tide. The transect starts out in the channel before heading into the shallow bank and finally turning back towards the channel. Elevated TSS levels (~50mg/L) are still apparent in and immediately adjacent to the shallow banks. This elevated TSS is likely due to a combination of the direct dredge plume and re-suspension of bed material from the banks. As discussed in Section 4.2, the bed material adjacent to the excavation works being undertaken by the Big Boss had greater fines content than the bed material adjacent to the Razende Bol. The higher fines content would result in a plume that takes longer (and further) to settle out of suspension. The higher fines content would also result in a greater level of background sediment re-suspension from the banks. Figure 4-18 Big Boss Flood Tide Plume Section (near-field)

30 BACK-HOE DREDGE PLUMES Sediment Flux Estimates Figure 4-19 Big Boss Flood Tide Plume Section (far-field) Net plume sediment flux was derived from appropriate ADCP cross-section transects and is summarised in Table 4-2 below. Calculation of the net plume sediment flux involved integration of the plume-only (background-removed) sediment flux across the transect. In performing the integration the top bin value was extrapolated to the surface. The sediment fluxes estimated from the ADCP measurements have a mean value of 4.7 kg/s, a standard deviation of 3.8 kg/s and a median value of 3.3 kg/s. This indicates that there is a very significant variation in the back-hoe dredge plume flux with time. This is to be expected given the sporadic nature of plume generation by the back-hoe dredging process. The sediment fluxes estimated from the ADCP measurements are generally consistent with the adopted time-averaged source rate of 3kg/s used in the DMP assessments (BMT WBM 2011a).

31 BACK-HOE DREDGE PLUMES 4-15 Table 4-2 Suspended Plume Sediment Flux Estimates Time Plume Flux (kg/s) Dredge Name Distance from Dredge (m) 13/07/ : Razende Bol ~50m 13/07/ : Razende Bol ~150m 13/07/ : Razende Bol ~50m 13/07/ : Razende Bol ~50m 13/07/ : Razende Bol ~50m 13/07/ : Razende Bol ~180m 13/07/ : Razende Bol ~220m 13/07/ : Razende Bol ~180m 13/07/ : Razende Bol ~50m 13/07/ : Big Boss ~50m 13/07/ : Big Boss ~270m 13/07/ : Big Boss ~50m 13/07/ : Big Boss ~50m 13/07/ : Big Boss ~50m 14/07/ : Razende Bol ~50m Mean: 4.7 Std Deviation: 3.8 Median: 3.3

32 PLUME MODEL VALIDATION PLUME MODEL VALIDATION 5.1 Overview Validation of the TUFLOW-FV dredge plume model was undertaken for the dredge plume dataset/s described above. Model tidal water level boundary conditions were derived from measured tides at the MSQ South Trees gauge using established correlations. Measured wind conditions at Gladstone airport were also applied to the model. The model validation simulation used the source and sediment fraction parameters derived for the EIS and DMP assessments (BMT WBM, 2009; BMT WBM 2011a), as shown in Table 5-1. Table 5-1 Dredge Plume Model Sediment Fractions and Settling Parameters Particle Fine Sand Silt Clay Still Water Fall Velocity, w s0 (m/s) 1.0E E E-05 Equivalent Stokes Diameter, d s0 (ηm) Critical Shear Stress Deposition, cd (N/m 2 ) Sediment particle density, s (kg/m 3 ) % Long Term Disposal Plume TUFLOW-FV was run in both 2D and 3D configurations for the validation assessments. As found in Section 2, both 2D and 3D model configurations produced very similar depth-averaged outputs and therefore only the 3D depth-averaged results are compared with the data below. 5.2 Back-Hoe Dredge Back-hoe dredge plumes were simulated for the monitoring period of 13th-14th July 2011 plus a suitable warmup period. The region of the model in the vicinity of the Big Boss and the Rashende Bol generally has mesh cells with dimensions between m, which limits the ability to resolve plume features less than this scale. The cell area receiving the Big Boss suspended sediment source was approximately 5,400m 2, whereas the Rashende Bol source was input into a cell with an area of 8,700m 2. Consequently the modelled Rashende Bol plumes exhibit greater near-field dilution than the Big Boss plumes. This modelled difference in plume concentrations is also due to the larger throughflows and hence higher flushing rates in the vicinity of the Rashende Bol. A continuous plume source rate of 3kg/s was assumed for each back-hoe dredge in order to be consistent with the assumed rate for the DMP water quality impact assessments (BMT WBM 2011a). As discussed in Section 4.5 the measured sediment flux rates showed substantial variation but were generally consistent with the rate assumed for modelling.

33 PLUME MODEL VALIDATION 5-2 Figure 5-1 shows the measured depth-averaged TSS from the ADCP transects minus the background TSS concentrations. Figure 5-2 shows the maximum modelled TSS from the monitoring period of 13th-14th July It can be seen that the model predicts greater plume extents than was measured during operations in the field. Instantaneous snapshots of modelled TSS concentration are compared with individual ADCP transects in Appendix C, with some particular transects shown below in Figure 5-3 to Figure 5-7. In general the following conclusions can be made about the modelled and measured back-hoe plume comparisons: Near-field plume dilution and correspondingly plume width are over-predicted by the model; Consequently, near-field plume concentrations are generally under-predicted by the model; Mid to far-field plume concentrations are generally comparable or higher than the measured concentrations above background levels; and Modelled mid to far-field plume width is generally larger than the comparable measured plume widths. Regarding the first point, near-field under-prediction of the peak plume concentrations is expected in a broad-scale model such as described here. Initial model dilution of the plume occurs over an entire model cell, which is significantly larger than the near-source plume size. The model/data comparisons shown here indicate that in the medium to far-field, the model inaccuracies due to finite resolution become less significant due to the natural flow dispersion and turbulent diffusion processes that result in horizontal mixing of the plume. In the mid to far-field the modelled plume centreline concentrations are consistent with or higher than the measured concentrations above background levels and the plume width is slightly over-predicted. These results provide confidence that the dredge plume impacts are conservatively predicted using the model (as described) in combination with a reasonable estimate of plume source loading.

34 PLUME MODEL VALIDATION 5-3 Figure 5-1 Measured Plume Only TSS - All ADCP Transects (13/07-14/07) Figure 5-2 Modelled Maximum Plume Only TSS (13/07-14/07)

35 PLUME MODEL VALIDATION 5-4 Figure 5-3 Razende Bol Model vs ADCP Plume Only TSS Comparison (near-field) Figure 5-4 Razende Bol Model vs ADCP Plume Only TSS Comparison (mid-field)

36 PLUME MODEL VALIDATION 5-5 Figure 5-5 Razende Bol Model vs ADCP Plume Only TSS Comparison (long-section) Figure 5-6 Big Boss Model vs ADCP Plume Only TSS Comparison (near-field)

37 PLUME MODEL VALIDATION 5-6 Figure 5-7 Big Boss Model vs ADCP Plume Only TSS Comparison (mid-field)

38 SUMMARY SUMMARY The following conclusions can be drawn from the work undertaken and described in this report: 2D and 3D hydrodynamic and plume simulations generate similar predictions in the macro-tidal and well-mixed waters of Port Curtis; 3D plume simulations explicitly resolve vertical-distributions of currents and plume suspended sediments and can therefore provide additional information to the impact assessment (where required); Measured back-hoe dredge plume source rates varied significantly but were generally consistent with the 3kg/s assumed in the DMP; Measured back-hoe dredge plumes were observed to merge with background TSS/turbidity levels within 500m of source; Mid to far-field back-hoe plume characteristics were generally conservatively predicted by the model, i.e. the model provided an over-estimate of the impacts; Near-field plume dilutions are generally over-predicted by the broad-scale plume model.

39 REFERENCES REFERENCES Aurecon, Western Basin Project Dredging and Offshore Disposal Works (Stage 1) Water Quality Management Plan. Report Prepared for Gladstone Ports Corporation. Report , April BMT WBM, Gladstone Western Basin EIS Numerical Modelling Studies. Report Prepared for Gladstone Ports Corporation. R.B Impact_Assessment.doc, September BMT WBM, 2011a. Gladstone Western Basin Dredging Plume Dispersion Modelling. Report Prepared for Gladstone Ports Corporation. R.B Plume_Dispersion.doc, January BMT WBM. 2011b. Gladstone Harbour Numerical Modelling and Calibration and Validation. Report Prepared for Gladstone Ports Corporation. R.B Model_Validation.doc. March GHD, Western Basin Dredging and Disposal Project Environmental Impact Statement. Report prepared for Gladstone Ports Corporation. GHD, Brisbane. GHD, Western Basin Dredge and Disposal Project - Supplementary Environmental Impact Statement. Report prepared for Gladstone Ports Corporation. GHD, Brisbane. Herzfeld, M., Parslow, J., Andrewartha, J., Sakov, P. and Webster, I. T., Hydrodynamic Modelling of the Port Curtis Region. CRC for Coastal Zone, Estuary and Waterway Management. Technical Report 7.

40 TUFLOW-FV 3D HYDRODYNAMIC VALIDATION A-1 APPENDIX A: TUFLOW-FV 3D HYDRODYNAMIC VALIDATION

41 TUFLOW-FV 3D HYDRODYNAMIC VALIDATION A-2 1 ADCP Site 1 Current Speed (m/s) /05/ /05/ /05/ /05/ /06/ /06/ /06/ /06/2009 ADCP Site 1 model 2D model 3D Current Speed (m/s) ADCP Site /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/2009 ADCP Site 1 model 2D model 3D 360 ADCP Site Current Direction (Degrees true) /05/ /05/ /05/ /05/ /06/ /06/ /06/ /06/2009 ADCP Site 1 model 2D model 3D 360 ADCP Site Current Direction (Degrees true) /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/2009 ADCP Site 1 model 2D model 3D

42 TUFLOW-FV 3D HYDRODYNAMIC VALIDATION A-3 1 ADCP Site 2 Current Speed (m/s) /05/ /05/ /05/ /05/ /06/ /06/ /06/ /06/2009 ADCP Site 2 model 2D model 3D Current Speed (m/s) ADCP Site /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/2009 ADCP Site 2 model 2D model 3D 360 ADCP Site Current Direction (Degrees true) /05/ /05/ /05/ /05/ /06/ /06/ /06/ /06/2009 ADCP Site 2 model 2D model 3D 360 ADCP Site Current Direction (Degrees true) /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/2009 ADCP Site 2 model 2D model 3D

43 TUFLOW-FV 3D HYDRODYNAMIC VALIDATION A-4 1 ADCP Site 3 Current Speed (m/s) /05/ /05/ /05/ /05/ /06/ /06/ /06/ /06/2009 ADCP Site 3 model 2D model 3D Current Speed (m/s) ADCP Site /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/2009 ADCP Site 3 model 2D model 3D 360 ADCP Site Current Direction (Degrees true) /05/ /05/ /05/ /05/ /06/ /06/ /06/ /06/2009 ADCP Site 3 model 2D model 3D 360 ADCP Site Current Direction (Degrees true) /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/2009 ADCP Site 3 model 2D model 3D

44 BACK-HOE DREDGE MONITORING B-1 APPENDIX B: BACK-HOE DREDGE MONITORING Sediview Calibration Day 1 Sediview Calibration Day 2

45 BACK-HOE DREDGE MONITORING B-2

46 BACK-HOE DREDGE MONITORING B-3

47 BACK-HOE DREDGE MONITORING B-4

48 BACK-HOE DREDGE MONITORING B-5

49 BACK-HOE DREDGE MONITORING B-6

50 BACK-HOE DREDGE MONITORING B-7

51 BACK-HOE DREDGE MONITORING B-8

52 BACK-HOE DREDGE MONITORING B-9

53 BACK-HOE DREDGE MONITORING B-10

54 BACK-HOE DREDGE MONITORING B-11

55 BACK-HOE DREDGE MONITORING B-12

56 BACK-HOE DREDGE MONITORING B-13

57 BACK-HOE DREDGE MODEL VALIDATION C-1 APPENDIX C: BACK-HOE DREDGE MODEL VALIDATION

58 BACK-HOE DREDGE MODEL VALIDATION C-2

59 BACK-HOE DREDGE MODEL VALIDATION C-3

60 BACK-HOE DREDGE MODEL VALIDATION C-4

61 BACK-HOE DREDGE MODEL VALIDATION C-5

62 BACK-HOE DREDGE MODEL VALIDATION C-6

63 BACK-HOE DREDGE MODEL VALIDATION C-7

64 BACK-HOE DREDGE MODEL VALIDATION C-8

65 BACK-HOE DREDGE MODEL VALIDATION C-9

66 BACK-HOE DREDGE MODEL VALIDATION C-10

67 BACK-HOE DREDGE MODEL VALIDATION C-11

68 BACK-HOE DREDGE MODEL VALIDATION C-12

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