EIA Report Annexured 24.08

Table 4-1 Extreme Estimates of 1-hour Average Wind Speed u10 1hr at 10 m Height from Analysis of Continuous 1 Year Model Hindcast 4-2 Table 4-2 Extrem...

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LNG Import Terminal at Pipavav Environment Impact & Risk Assessment – Executive Summary

Annexure F:

Met-Oocean and

Sedimentation Study

INDOMER

A part of BMT in Energy and Environment

Metocean and Sedimentation Study for LNG Import Terminal, Pipavav, India R.B17825.001.01.MetoceanReport.doc March 2011

Metocean and Sedimentation Study for LNG Import Terminal, Pipavav, India

Offices

Prepared For:

Swan Energy Limited

Prepared By:

BMT WBM Pty Ltd

(Member of the BMT group of companies)

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Brisbane Denver Mackay Melbourne Newcastle Perth Sydney Vancouver

CONTENTS

I

CONTENTS Contents

1

i

List of Figures

iii

List of Tables

iv

INTRODUCTION

1-1

1.1

1-1

Scope of Assessments Undertaken

2

EXISTING CONDITIONS

2-1

3

NUMERICAL MODELLING

3-1

3.1

Digital Elevation Model

3-1

3.2

SWAN Wave Modelling

3-2

3.3

Hydrodynamic Modelling

3-2

3.4

3.5

4

5

3.3.1

Regional Gulf of Khambhat Model

3-3

3.3.2

Local Pipavav Model

3-3

3.3.3

Model Calibration

3-3

Sediment Transport Modelling

3-4

3.4.1

Model Establishment

3-4

3.4.2

Model Calibration

3-5

Wave Penetration Modelling

3-6

3.5.1

Model Domain

3-6

3.5.2

Wave Reflection

3-6

3.5.2.1

Wave Penetration Model Scenarios

3-7

3.5.2.2

BOUSS-2D Modelling Results

3-8

METOCEAN CRITERIA

4-1

4.1

Approach

4-1

4.2

Results

4-1

4.3

Conclusions

4-6

4.4

Recommendations

4-8

WAVE DISTURBANCE ASSESSMENT

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5-1

CONTENTS

6

II

5.1

Methodology

5-1

5.2

Wave Climate at Port Entrance

5-1

5.3

Operational Wave Height Limits

5-2

5.4

Operational Downtime Calculations

5-3

IMPACT ASSESSMENT

6-1

6.1

Hydrodynamics

6-1

6.2

Bed Shear Stress

6-1

6.3

Siltation

6-2

6.4

Littoral Transport Processes

6-3

7

CONCLUSIONS AND RECOMMENDATIONS

7-1

8

REFERENCES

8-1

9

GLOSSARY

9-1

APPENDIX A: HYDRODYNAMIC MODEL CALIBRATION

A-1

APPENDIX B: SEDIMENTATION CALIBRATION

B-1

APPENDIX C: AMBIENT WAVE CLIMATE AT PORT ENTRANCE

C-1

APPENDIX D: MODELLED WAVE PENETRATION COEFFICIENTS

D-1

APPENDIX E: WAVE DISTURBANCE CALCULATIONS

E-1

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LIST OF FIGURES

III

LIST OF FIGURES Figure 2-1

Satellite Image of Study Area

Figure 3-1

Digital Elevation Model

3-10

Figure 3-2

Nested SWAN Wave Models (top) and Regional Indian Ocean Wave Model Grid (bottom)

3-11

Gulf of Khambhat (top) and Pipavav (bottom) Hydrodynamic Model Meshes

3-12

Figure 3-4

NIOT March 2007 Field Deployment Locations

3-13

Figure 3-5

NIOT September 2007 Field Deployment Locations

3-13

Figure 3-6

Water Level Comparison at Location TG6 (March 2007)

3-14

Figure 3-7

Current Meter Comparisons at Location C6 and C12 (September-October 2007)

3-14

Comparison of Modelled TSS with Comacoe 2010 Measurements (Upper bound model results multiplied by 4)

3-15

Comparison of Modelled TSS with NIOT Measurements during March 2007 Spring Tides (Upper bound model results multiplied by 4)

3-16

Figure 3-10

2001 Bathymetry Sedimentation Validation

3-17

Figure 3-11

Existing Configuration Bathymetry (top) and Modelled Sedimentation (bottom)

3-18

Figure 3-12

BOUSS-2D Wave Model Layouts

3-19

Figure 3-13

Bathymetry of Proposed Port Layout (150 degree model)

3-20

Figure 3-14

Output Locations - BOUSS-2D Modelling

3-21

Figure 3-15

3D View of Wave Propagation (looking to North West)

3-22

Figure 3-16

Modelled Significant Wave Height Run "PIP_Dogleg_SE_Tp06_150deg"

3-23

Modelled Wave Penetration Coefficient Run " PIP_Dogleg_SE_Tp06_150deg"

3-23

Figure 3-3

Figure 3-8 Figure 3-9

Figure 3-17

2-2

Figure 4-1

Pipavav Nearshore Points of Interest

Figure 4-2

Time Series of Principal Hindcast Wave and Wind Parameters for Nearshore Location 1 (Full Year 2007)

4-10

Time Series of Principal Hindcast Wave and Wind Parameters for Nearshore Location 1 (SW Monsoon Season 2007)

4-11

Loc 1 All-Year 10-Min Mean Wind Rose (m/s at 10m ASL, top) and Loc 1 All-Year Hs Wave Rose (m, bottom)

4-12

Figure 4-3 Figure 4-4

4-9

Figure 4-5

West Coast of India Historical Tropical Revolving Storm Trajectories 4-13

Figure 4-6

West Coast of India Tropical Revolving Storm Trajectories Selected for Model Hindcasting

4-13

Time Series of Principal Hindcast Wave and Wind Parameters for Nearshore Loc 1 (Tropical Storm 1)

4-14

Time Series of Tidal and Storm Residual Current and Water Level Parameters for Nearshore Loc 1 (Tropical Storm 1)

4-15

Figure 4-7 Figure 4-8 Figure 6-1

Layouts of Previously Assessed Port Configurations

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6-4

LIST OF TABLES

IV

Figure 6-2

Layout of Proposed Development

6-4

Figure 6-3

Typical Spring Tide Flood Current Distribution Top: Existing Case, Centre: Developed Case, Bottom: Difference

6-5

Typical Spring Tide ebb Current Distribution Top: Existing Case, Centre: Developed Case, Bottom: Difference

6-6

Median Bed Shear Stress Distribution Top: Existing Case, Centre: Developed Case, Bottom: Difference

6-7

Sediment Deposition Rate under Ambient Conditions Top: Existing Case, Centre: Developed Case, Bottom: Difference

6-8

Sedimentation Summary Zones

6-9

Table 2-1

Tidal Planes, Pipavav Port

2-1

Table 3-1

Wave Reflection Coefficients within Port Basin

3-7

Table 3-2

Modelled Wave Scenarios - BOUSS-2D Modelling

3-8

Table 3-3

Modelled Wave Penetration Coefficients

3-9

Table 4-1

Extreme Estimates of 1-hour Average Wind Speed u101hr at 10 m Height from Analysis of Continuous 1 Year Model Hindcast

4-2

Extreme Estimates of 10-minute Average Wind Speed u1010min at 10 m Height

4-3

Extreme Estimates of Significant Wave Height at Location 1 from Analysis of Continuous 1 Year Model Hindcast

4-4

Extreme Estimates of Associated Wave Spectral Peak Period at Location 1 from Analysis of Continuous 1 Year Model Hindcast

4-5

Extreme Estimates of Surface Current Speed at Location 1 from Analysis of Continuous 1 Year Model Hindcast

4-6

Table 4-6

Extreme Tidal Elevations

4-6

Table 4-7

Recommended Preliminary Extreme Wind and Wave Conditions at Location 1

4-7

Table 4-8

Extreme Surface Current Conditions at Location 1

4-7

Table 4-9

Extreme Water Levels at Location 1

4-8

Table 5-1

Operational Wave Height Limits

5-3

Table 6-1

Estimated Sedimentation Rates

6-3

Figure 6-4 Figure 6-5 Figure 6-6 Figure 6-7

LIST OF TABLES

Table 4-2 Table 4-3 Table 4-4 Table 4-5

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1-1

INTRODUCTION

1

INTRODUCTION This report details work undertaken by BMT towards development of preliminary Metocean criteria and preliminary assessment of impacts associated with a proposed LNG Import facility near the Port of Pipavav in India. These assessments were undertaken in the context of a broader feasibility assessment.

1.1

Scope of Assessments Undertaken This study includes the following components: •



Establishment of numerical models to simulate: o

Wave generation, propagation and nearshore transformation in the Gulf of Khambhat;

o

2D Hydrodynamics at two different domain scales: ƒ

Gulf of Khambhat; and

ƒ

Pipavav coastal waters.

o

Sediment transport in and around Pipavav Port; and

o

Harbour wave penetration.

Development of preliminary Metocean Criteria for Ambient and Extreme conditions, including: o

Wind;

o

Waves;

o

Currents; and

o

Water levels.



Wave penetration and terminal operability assessment for the proposed harbour layout;



Assessments of potential impacts of the proposed harbour development, including: o

Hydrodynamics (currents);

o

Bed shear stresses;

o

Sedimentation; and

o

Littoral transport processes.

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2-1

EXISTING CONDITIONS

2

EXISTING CONDITIONS Pipavav is subjected to increased winds and persistent south westerly swell waves during the south west monsoon period (June to August). During the rest of the year, conditions are generally quite benign. Tropical revolving storms occur infrequently in the northern Indian Ocean, but can cause significantly enhanced local wind speeds, sea state, water level and current velocities at Pipavav. Tidal planes for Pipavav Port are as follows (from BMTCI, Site Selection Study for LNG Import Operations at Pipavav, June 2009). Table 2-1

Tidal Planes, Pipavav Port

Tidal range at Pipavav (around 3.5 m for a spring tide) is modest relative to the higher tidal variations experienced further north in the Gulf of Khambat. These tidal variations generate currents of the order of 0.5 to 1 m/s within the study area (with variations due to coastal features, bathymetry, etc). The flood stage of the tide is alongshore in a north-easterly direction and the ebb stage is to the south-west. Predicted currents in the vicinity of the proposed facility are relatively uniform, especially so further offshore. Nearer to the coastline, local coastal features tend to disrupt flows and create eddies and circulation patterns. Similarly at Pipavav Port, the existing jetty structure and the island of Shial Bet create disturbances in the broader flow directions, creating localised, complex current patterns that vary over the tidal stages. Wetting and drying of the intertidal flats adjacent to the coastline is a notable feature; of the order of 200 to 500 m of flats is exposed along the coast at a typical low tide. TSS measurements show elevated suspended sediment concentrations. It is likely that very fine sediments persist in the water column, creating a background ambient suspended sediment concentration that would occur on a regional spatial scale. This would especially be the case during periods of above normal wind and wave conditions. These fine sediments would be highly mobile and would tend to deposit in zones of unnaturally low bed shear stress, such as in dredge channels and behind breakwaters and similar structures. Coarser material is also expected to be transported in the study area. This would tend to be less mobile (only during peak flood and ebb stages of the tide, or during heavy seas associated with monsoonal climatic conditions).

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2-2

EXISTING CONDITIONS

A satellite image of the study area is shown in Figure 2-1. There is evidence of a buildup of sediments on both the northern and southern sides of the main jetty at Pipavav Port. The highest accumulation appears to be to the north; sediment feed from the adjacent estuary may be a minor contributing factor. Apart from this, there does not appear to be any coastal features that show noticeable shoreline buildup or retreat; this suggests that littoral transport rates, in either northerly or southerly directions (gross or net), are not significant.

Figure 2-1

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Satellite Image of Study Area

NUMERICAL MODELLING

3

3-1

NUMERICAL MODELLING Various numerical models were developed, calibrated and validated as part of this study (further discussion on each in subsequent sections):

3.1



Digital Elevation Model, which was used to inspect the numerical model bathymetry inputs;



SWAN wave models to translate ocean swell and wind generated waves into the Gulf of Khambhat and to the study site near Pipavav – nested into regional/global spectral wave model;



TUFLOW-FV hydrodynamic model to predict tidal and meteorologically driven water levels and currents at the study site and impacts of the proposed development;



TUFLOW-FV cohesive sediment transport model to predict changes to the sediment transport regime and the potential for siltation of the proposed facility; and



BOUSS-2D wave penetration model of the harbour.

Digital Elevation Model A Digital Elevation Model (DEM) of the Gulf of Khambhat was derived from the following data sources: •

British Admiralty Charts: 2736, 1486, 1474;



Indian National Hydrographic Office Chart 2081;



Pipavav Port hydrographic survey datasets undertaken from 2001 to 2007 and provided by NIOT; and



Hydrographic survey undertaken for Swan Energy Ltd by Coastal Marine Construction and Engineering Ltd.

Unless otherwise stated it was assumed that all datasets were vertically referenced to a local Chart Datum. These datasets were digitised (where required), and collated into a regional scale Gulf of Khambhat DEM with a 50m grid-size and a detailed 10m DEM of Pipavav coastal waters as shown in Figure 3-1. Tidal station data from standard port locations around the Gulf of Khambhat were used to prepare a continuous conversion from Chart Datum (CD) to Mean Sea Level (MSL) datum. The final DEMs and all numerical models were referenced to a MSL datum. Discrepancies were found between chart data and the recent hydrographic survey datasets; at the western extent of the hydrographic survey (to the west of the final proposed harbour layout, as shown in Figure 3-1) there is a relatively sharp transition in bed levels. While the discussions, recommendations and conclusions drawn from the hydrodynamic and sedimentation models are considered reliable and valid, it is possible that this transition may have some influence. Any future studies should consider an extension of the hydrographic survey exercise further west than the existing survey extent. The final DEMs were used to point inspect the bathymetry at the numerical model computation points.

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NUMERICAL MODELLING

3.2

3-2

SWAN Wave Modelling A series of three nested SWAN model grids to simulate wave conditions in the Pipavav proposed development area. These are shown in Figure 3-2, together with the BMT ARGOSS global wave model grid for the Indian Ocean, which provided spectral boundary conditions to the SWAN modelling. Hydrodynamic data (currents and water levels) were derived from the TUFLOW FV model and applied as input to the SWAN models. The BMT global wave model is based on the WAVEWATCH-3 system. NCEP forcing wind fields are pre-calibrated against satellite scatterometer data, and resultant wave fields are further calibrated against concurrent satellite altimeter observations. The in-situ measured wave data available at Pipavav did not cover the south west monsoon period, and were therefore of very limited use in model validation as they only encompassed benign sea state conditions. BMT ARGOSS wind fields and tidal constants were used as boundary conditions for the TUFLOWFV hydrodynamic model. The resultant current and water level data were used in the SWAN model runs to allow simulation of wave/current interaction and variable water depth; both of these factors are of importance in describing the wave characteristics in the Pipavav development area. The boundary tidal constants were derived from BMT’s global tidal model. This utilises quality-controlled long-term data from satellite altimeter missions, together with in-situ observations from more than 5000 coastal gauges.

3.3

Hydrodynamic Modelling Hydrodynamic models were developed at two different domain scales; a regional model of the Gulf of Khambhat, and a nested model of Pipavav coastal waters. The hydrodynamic model software used in this study was TUFLOW-FV, which solves the non-linear shallow water equations including solute transport by advection-dispersion in 2D or 3D on a flexible mesh, comprised of quadrilateral and triangular elements, using a finite-volume numerical scheme. Advantages of this scheme include: •

Flexible mesh resolution;



Local and global conservation of mass (to floating point precision) even in regions of wetting and drying;



Robust and accurate solutions for mixed sub-critical/super-critical flows;



An ability to simulate 2D and 3D processes; and



An ability to parallel-process in order to reduce model run-times.

For the current study TUFLOW-FV has been run in a 2D depth-averaged configuration. A 2D hydrodynamic model is appropriate for the port of Pipavav due to the high-energy tidal regime, and low volume of freshwater inflows relative to the tidal prism under normal day to day conditions, which lead to a predominantly well-mixed water-column without significant temperature/salinity stratification. Some localised three-dimensionality of the flow would still be expected in the vicinity of abrupt bathymetric transitions, However, a 2D model is appropriately detailed for the feasibility assessments undertaken for this study.

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NUMERICAL MODELLING

3.3.1

3-3

Regional Gulf of Khambhat Model A regional Gulf of Khambhat hydrodynamic model was established and run in order to provide water level and current boundary conditions for a nested model of Pipavav coastal waters. The mesh resolution of the regional model ranged from around 6km at the open boundary to less than 1km along the coastline and in the Upper Gulf, with a mean cell side dimension of around 2km. The open boundary conditions for the regional hydrodynamic model were generated from 8 tidal constituents extracted from the BMT ARGOSS global tide database. The tidal amplitude and phasing varies significantly along the 300 km open ocean boundary and thus water levels were generated from constituents extracted at 23 locations along the boundary. Wind and pressure fields derived from the National Centre for Environmental Prediction (NCEP) / National Centre for Atmospheric Research (NCAR) Reanalysis 2 global data set were applied over the Gulf of Khambhat model domain. The regional model was calibrated to reproduce tidal constituents derived from standard port tide gauge measurements throughout the Gulf of Khambhat1.

3.3.2

Local Pipavav Model A nested hydrodynamic model of Pipavav coastal waters was developed with boundaries extending from near Jafarabad in the west to Patva in the east. The mesh resolution of this model ranged from 500m offshore to better than 20m where required in and adjacent to the study area. The mean cell side dimension for this model was better than 100m. The open boundary conditions for this model were extracted from the regional hydrodynamic model output. Wind stresses were applied from the NCEP/NCAR Reanalysis 2 windfield.

3.3.3

Model Calibration The Pipavav model was calibrated to an array of water level and current measurements obtained from a field deployment by NIOT in March-April 2007. Validation of the model was performed against a second field deployment dataset obtained by NIOT in September-October 2007. The full model calibration and validation results are provided in Appendix A. Specific results from the full calibration exercise are shown in the following figures: •

Figure 3-4 shows the location of the NIOT field instrument deployments;



Figure 3-6 compares the model water level predictions with measurements at TG6 during the first deployment. This tide gauge was located adjacent to the Pipavav Port reclamation; and



Figure 3-7 compares the model current speed predictions with measurements at both CM6 and CM12 during the second deployment. These current meters are located to the west of Pipavav Port in the vicinity of the proposed Swan Energy development.

1

The results of this regional calibration are not shown in this report. Demonstration of performance of the regional model in providing boundary conditions to the local model is part of the local model calibration.

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NUMERICAL MODELLING

3-4

The calibration exercise demonstrates good overall performance of the model in predicting water levels and currents in the study area. In the area of the proposed new facility (locations CM6 and C12), model predictions are in particularly good agreement to measurements. Modelled velocities are lower than measured at two locations in the channel between the mainland and Shial Bet during the March deployment (CM2 and CM5) and at two locations during the September deployment (CM2 and CM9). This may indicate that the model is underpredicting currents passing through the channel, although it is difficult to confirm this for the following reasons: •

Other locations in the channel show acceptable comparisons between measured and modelled current speeds;



Current meters were known to have dragged moorings during the NIOT deployments and the precise location of the measurements is impossible to verify;



The high currents tend to tilt the current meters, thereby resulting in errors dependent of the varying speed through the tidal cycle; and



The channel itself, with its specific geometry and bathymetric features, may experience localised strongly three-dimensional hydrodynamic effects. As a consequence of this: o

The adopted modelling approach (2D, at around a 20 m resolution) may not fully capture these effects; and/or

o

The adopted measurements are from single point current meters, installed around middepth, which may not be truly representative of depth averaged velocities.

Despite these uncertainties, in general the hydrodynamic calibration exercise demonstrates a good model performance at a level of accuracy that is appropriate (or better than appropriate) for the present study.

3.4

Sediment Transport Modelling

3.4.1

Model Establishment The cohesive sediment module of TUFLOW-FV performs the following tasks: •

Tracking the sediment quantity and composition of (multiple) seabed sediment layers;



Tracking (multiple) sediment fractions in the water column; and



Tracking sediment exchange between the water column and the seabed: o

Erosion; and

o

Deposition.

This is achieved using the underlying hydrodynamic and wave models as the primary drivers of sediment mobilisation, settling and movement. A range of options for modelling these processes are available within the cohesive sediment module, however only those parameterisations used in the Pipavav siltation modelling assessments are

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NUMERICAL MODELLING

3-5

described below. Model parameter values have been determined through a process of model calibration and remain within accepted bounds from relevant literature. Values assigned to key parameters are as follows: •

Fine sand fraction is 70% of initial bed sediment and boundary condition concentrations;



Silt fraction is 30% of initial bed sediment and boundary condition concentrations;



Fine sand fraction settling velocity = 1.0 cm/s;



Silt fraction settling velocity = 0.5 mm/s;



Critical bed shear stress for settling = 0.1 N/m2; and



Critical bed shear stress for resuspension = 0.2 N/m2.

The model was initially run for an extended period in order to achieve a dynamically stable initial condition for the bed. This “warmup” effectively conditioned the bed composition to be consistent with the simulated hydrodynamic conditions, i.e. bed shear stresses. Without the warmup the modelled siltation patterns are very dependent on the specified initial conditions, which is undesirable if the benthic sediment has not been mapped in sufficient detail.

3.4.2

Model Calibration The sediment transport model has been calibrated against available Total Suspended Solids (TSS) data from Pipavav and surrounds. There is a wide variation in measured TSS; for example measurements by NIOT in 2007 show TSS levels in excess of 1200 mg/L during spring tide periods. In comparison, more recent measurements by Comacoe Pty Ltd (2010) measured peak TSS of around 300 mg/L under similar tidal conditions. This variation raises concerns about the consistency of available datasets, and/or potentially indicates that other processes influence TSS (such as annual variability, etc) which are not directly modelled. The model boundary conditions and bed erosion rates have been initially tuned to provide TSS estimates consistent with the more recent Comacoe measurements. The comparison to these values is shown in Figure 3-8. As shown, modelled TSS is comparable to measurements. Model results underpredict TSS measurements from the March 2007 field instrument deployment undertaken by NIOT. Figure 3-9 shows the comparison at CM5 and CM6, which are the two closest locations to the proposed Swan Energy development. Other plots are shown in Appendix B. For each plot, two model curves are presented; the model predictions and also model predictions multiplied by a factor of 4. Model results are more consistent to the NIOT measurements when this factor is applied. The application of the multiplier for comparison to NIOT measurement underscores the uncertainties associated with the assessment; the model was tuned to the Comacoe data and hence produces TSS values consistent with these measurements. NIOT measurements are around 4 times higher; model parameters could quite justifiably be tuned to match these measurements, however the model in its present form cannot match both sets of measurements. As such, the factored results should be considered as a more conservative estimate. Further data collection and analyses would be required to provide further clarity.

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NUMERICAL MODELLING

3-6

An additional check of model performance in predicting siltation rates was done to observations derived from hydrographic surveys performed in 2001 and 2003, which provide average siltation rates in the dredge basin of Pipavav Port (see Figure 3-10). A model simulation period of 1 month was simulated for typical conditions (standard tidal variations and no monsoonal activity) and the siltation rates extrapolated to represent a 2 year period. The comparison of extrapolated bed levels, shown in Figure 3-10, demonstrates a consistency between model predictions and observed siltation rates (which are significant in this area). A different (more even) spatial distribution of sedimentation would have been generated if the model simulation was continued for longer than 12 months as opposed to the extrapolation undertaken here (the computational requirements to simulate a 2 year period of morphological update were prohibitive in this case). Importantly however, modelled sedimentation reasonably predicts gross sedimentation volumes in the dredge cut. The distribution of modelled siltation shown in Figure 3-11 is consistent with a qualitative understanding of sedimentation within the Port of Pipavav, and in particular with the following points:

3.5



The channel between Pipavav Port and Shial Bet is in a relatively stable state;



The Pipavav Port berth pocket/s do not experience significant sedimentation; and



Some sedimentation is predicted to occur behind the berth pocket in the vicinity of the stub breakwater.

Wave Penetration Modelling To assess the wave propagation into the proposed harbour basin, numerical wave penetration modelling was undertaken using the modelling software BOUSS-2D. BOUSS-2D is a comprehensive numerical model that solves Boussinesq-type hydrodynamic equations and is specifically oriented at problem solving involving reflection/diffraction of waves in semi-enclosed basins such as in ports and harbours. The BOUSS-2D engine is developed by US Army Corps of Engineers. Phenomena included in BOUSS-2D are: shoaling, refraction, diffraction, full/partial reflection and transmission, bottom friction, wave breaking and runup, wave-induced currents and wave-current interaction.

3.5.1

Model Domain Three BOUSS2D wave models were established to investigate the wave penetration into the proposed port layout. The model domains used are shown in Figure 3-12. The grid resolution of the "180 Degree" model was 5m by 5m and 4m by 4m for the "150 Degree" and "90 Degree" models. A three-dimensional view of the bathymetry and harbour layout is shown in Figure 3-13.

3.5.2

Wave Reflection Along the interface between water and land, some proportion of the incident wave energy may be reflected. Typically, vertical walls are almost fully reflective, while rubble-mound structures and

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NUMERICAL MODELLING

beaches absorb a significant portion of the incident energy. The reflection coefficient of rubble-mound structures is generally a function of the wave condition, the structure slope and roughness of the armour layers. The wave reflection coefficients of the perimeters of the proposed port basin have been estimated on methodologies recommended in the Coastal Engineering Manual (CEM, 2006). The CEM recommends use of a method by Seelig to estimate the reflection coefficient of rubble mound structures such as the proposed breakwaters and the revetment walls (Seelig, 1983). The jetties of the proposed LNG facility have been assumed to be fully permeable in the modelling. The adopted reflection values in the wave penetration modelling are presented in Table 3-1. The reflection characteristics of walls around the proposed harbour basin have been modelled in BOUSS-2D using damping layers. Table 3-1

Wave Reflection Coefficients within Port Basin

Section

Reflection Coefficient 15 to 40%

Breakwater Structures (Value depends on incident wave condition) 18 to 53% Revetments (Value depends on incident wave condition) Beach

15%

Vertical Walls

100%

3.5.2.1 Wave Penetration Model Scenarios A number of wave scenarios were simulated to assess the wave penetration coefficients at key locations of the port. The modelled wave scenarios are listed in Table 3-2. The BOUSS-2D model runs were run with an offshore water level at mean sea level and irregular, unidirectional waves. The incident waves at the open boundary were characterised by a JONSWAP spectrum with a peakedness parameter (gamma value) of 3.30.

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NUMERICAL MODELLING

Table 3-2

Modelled Wave Scenarios - BOUSS-2D Modelling

Model Run ID

Sea Wave or Swell

Offshore significant Wave Height

Peak Wave Period

Wave Direction

PIP_Dogleg_EE_Tp05_060deg

Sea

1.0 m

5.5 s

60°

PIP_Dogleg_EE_Tp05_090deg

Sea

1.0 m

5.5 s

90°

PIP_Dogleg_SE_Tp05_120deg

Sea

1.0 m

5.5 s

120°

PIP_Dogleg_SE_Tp06_150deg

Sea

1.0 m

6.0 s

150°

PIP_Dogleg_SS_Tp08_180deg

Sea

1.0 m

8.0 s

180°

PIP_Dogleg_SS_Tp12_210deg

Sea

1.0 m

12.0 s

210°

PIP_Dogleg_SS_Tp16_210deg

Swell

1.0 m

16.0 s

210°

3.5.2.2 BOUSS-2D Modelling Results Figure 3-15 to Figure 3-17 illustrate examples of BOUSS-2D simulation output, being the instantaneous water surface elevation and significant wave height for model run "PIP_Dogleg_SE_Tp06_150deg" (Offshore wave height of 1m, peak wave period of 6 seconds and wave direction from 150 degrees). BOUSS-2D model results were used to derive the wave penetration coefficient for each wave scenario modelled. Maps of the wave penetration coefficients are included in Appendix D. The modelled average wave penetration coefficients at the proposed berths are tabulated in Table 3-3 (Refer to Figure 3-14 for output locations). Analysing the results from the BOUSS-2D modelling, the following is noted: •

Due to the orientation of the port and the proposed breakwater arrangement, the port basin and the berths of the LNG terminal are generally well protected from the most severe incident wave height cases.



For some wave scenarios (particularly waves from 120 and 150 degree sectors), there is a "beam" of wave energy, which travels towards the proposed tug boat facility area.

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NUMERICAL MODELLING

Table 3-3

Modelled Wave Penetration Coefficients

FSRU - Terminal A

LNG - Terminal A

FSRU - Terminal B

LNG - Terminal B

Tug Boat Facility

Tug Boat Assistance Area

Location

PIP_Dogleg_EE_Tp05_060deg

13%

17%

16%

14%

3%

28%

PIP_Dogleg_EE_Tp05_090deg

8%

10%

33%

32%

14%

91%

PIP_Dogleg_SE_Tp05_120deg

3%

4%

6%

6%

17%

54%

PIP_Dogleg_SE_Tp06_150deg

3%

3%

5%

5%

29%

103%

PIP_Dogleg_SS_Tp08_180deg

2%

2%

3%

3%

10%

75%

PIP_Dogleg_SS_Tp12_210deg

1%

2%

3%

3%

5%

27%

PIP_Dogleg_SS_Tp16_210deg

2%

2%

4%

4%

8%

29%

Model Run ID

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NUMERICAL MODELLING

Figure 3-2

Nested SWAN Wave Models (top) and Regional Indian Ocean Wave Model Grid (bottom)

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NUMERICAL MODELLING

Figure 3-3

Gulf of Khambhat (top) and Pipavav (bottom) Hydrodynamic Model Meshes

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NUMERICAL MODELLING

Figure 3-4

Figure 3-5

NIOT March 2007 Field Deployment Locations

NIOT September 2007 Field Deployment Locations

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NUMERICAL MODELLING

TG6 water levels

DATA PIPAVAV model

2.50 2.00 1.50

tide (m MSL)

1.00 0.50 0.00 -0.50 -1.00 -1.50 -2.00 -2.50 09/03/07

11/03/07

13/03/07

15/03/07

17/03/07

19/03/07

21/03/07

23/03/07

25/03/07

27/03/07

Date

Figure 3-6

Water Level Comparison at Location TG6 (March 2007)

CM6 currents

DATA PIPAVAV model

2

1.5

current (m/s) +ve = flood tide

1

0.5

0

-0.5

-1

-1.5

-2 21/09/07

23/09/07

25/09/07

27/09/07

29/09/07

01/10/07

03/10/07

05/10/07

07/10/07

09/10/07

Date

CM12 currents

DATA PIPAVAV model

2

1.5

current (m/s) +ve = flood tide

1

0.5

0

-0.5

-1

-1.5

-2 09/10/07

11/10/07

13/10/07

15/10/07

17/10/07

19/10/07

21/10/07

23/10/07

25/10/07

27/10/07

Date

Figure 3-7

Current Meter Comparisons at Location C6 and C12 (September-October 2007)

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