ROBERTS BANK CONTAINER EXPANSION COASTAL …...two-dimensional hydrodynamic models for assessing project impacts associated with the Deltaport Third Berth Project. The terms of reference

ROBERTS BANK CONTAINER EXPANSION COASTAL GEOMORPHOLOGY STUDY

Appendix B

Prepared for: Vancouver Port Authority

Prepared by: northwest hydraulic consultants

30 Gostick Place North Vancouver, B. C.

V7M 3G2

In association with: Triton Consultants Ltd.

3530 West 43rd St. Vancouver, B. C.

V6N 3J9

November 2004 33863

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Coastal Geomorphology Study – Appendix B - i - November 2004

EXECUTIVE SUMMARY

This appendix summarizes the development, calibration, testing and verification of a suite of

two-dimensional hydrodynamic models for assessing project impacts associated with the

Deltaport Third Berth Project. The terms of reference for the study identified the area of interest

to be modelled as follows: “Extending north to the mouth of the main arm near Steveston, south

to Point Roberts, west to the 100 m depth contour and east to the highwater mark”. The model

development was carried out in three phases. The first phase involved tidal modelling studies in

the Strait of Georgia, Juan de Fuca Strait and around Vancouver Island using Tide2D. This

“Wide Area Model” was used to provide tidal height and tidal current boundary conditions along

a line in the deeper waters of Strait of Georgia parallel to Roberts Bank extending from just north

of Sandheads at the mouth of the Fraser River to the southern tip of Point Roberts. These

boundary conditions were used primarily to drive other detailed tidal models of the Roberts Bank

inter-causeway area.

The second phase involved developing a Base Model to simulate hydrodynamic conditions in the

Fraser estuary, Roberts Bank tidal flats and adjacent portions of the Strait of Georgia. This Base

Model was used to assess general flow patterns in the area of interest and to identify the potential

extent of impacts from various alternative project developments. Finally, a Detailed Model was

developed specifically for the Deltaport Third Berth Project to assess local flow conditions in the

Inter-causeway area between the Tsawwassen Ferry Terminal and Roberts Bank Causeway. This

Detailed Model was particularly useful for assessing shallow flows on the tidal flats and in

eelgrass covered areas as well as for assessing flow effects induced by structures such as the

proposed wharf extension at Deltaport Third Berth and the existing crest protection weir on the

tidal flats. The computational mesh for the Detailed Model has a resolution of between 5-10 m in

critical areas near the proposed developments in order to adequately represent project impacts

and complex flows in adjacent tidal drainage channels. The model was verified with a series of

ADCP current velocity measurements in April and May 2004. Comparisons between predicted

and measured velocities showed excellent agreement.

The results from the Detailed Model show that impacts of the proposed Deltaport Third Berth

Project on tidal currents would be very small. Local velocities are increased over an area

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Coastal Geomorphology Study – Appendix B - ii - November 2004

primarily in the immediate vicinity of the wharf extension. Local velocities will be decreased

over an area primarily behind the wharf extension. The magnitude of the velocities in the impact

zone is well below the threshold for any significant sediment transport. Therefore, we do not

expect significant morphological impacts to develop in response to changes in tidal flow

magnitude or direction.

Preliminary runs were made with the Base Model to assess the cumulative effects from other

proposed developments on the west side of the Roberts Bank Causeway (Terminal 2 Project) on

the Deltaport Third Berth Project. This analysis showed that preliminary configurations for

Terminal 2 could produce significant changes to the magnitude of tidal currents draining on the

west side of the causeway. However, the impacts did not extend into the inter-causeway area and

did not affect hydrodynamic conditions in the vicinity of the Deltaport Third Berth Project.

Therefore, in terms of representing hydrodynamic impacts, the two developments can be

assessed independently. More detailed modelling will be required to finalize the assessment of

local impacts from Terminal 2 project.

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Coastal Geomorphology Study – Appendix B - iii - November 2004

TABLE OF CONTENTS

1.0 INTRODUCTION............................................................................................................. 1

1.1 SCOPE OF WORK ...................................................................................................... 1

1.2 DELTAPORT THIRD BERTH PROJECT DESCRIPTION .................................................. 2

1.3 TERMINAL 2 PROJECT .............................................................................................. 3

1.4 METHOD OF APPROACH ........................................................................................... 3

1.5 ASSUMPTIONS AND LIMITATIONS ............................................................................ 4

2.0 WIDE AREA MODEL..................................................................................................... 6

2.1 MODEL DESCRIPTION............................................................................................... 6

2.2 MODEL DEVELOPMENT............................................................................................ 6

2.3 MODEL CALIBRATION.............................................................................................. 8

2.4 MODEL RESULTS ................................................................................................... 10

3.0 BASE MODEL................................................................................................................ 12

3.1 MODEL DESCRIPTION............................................................................................. 12

3.2 BASE MODEL DEVELOPMENT ................................................................................ 13

3.2.1 Work Carried Out ..................................................................................... 13

3.2.2 Boundary Conditions ................................................................................ 13

3.2.3 Roberts Bank and Project Geometry......................................................... 14

3.2.4 Model Verification.................................................................................... 16

3.2.5 Representative Tide Conditions................................................................ 18

3.2.6 Sensitivity Analysis .................................................................................. 19

3.3 MODEL RESULTS ................................................................................................... 19

3.3.1 Present Conditions .................................................................................... 19

3.3.2 Third Berth Project ................................................................................... 24

3.3.3 Terminal 2 Project..................................................................................... 24

4.0 DETAILED MODEL DEVELOPMENT ..................................................................... 27

4.1 MODEL DESCRIPTION............................................................................................. 27

4.2 MODEL DEVELOPMENT.......................................................................................... 27

4.2.1 Work Carried Out ..................................................................................... 27

4.2.2 Model Extent and Boundary Conditions................................................... 28

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Coastal Geomorphology Study – Appendix B - iv - November 2004

4.2.3 Topography and Project Geometry........................................................... 29

4.2.4 Vegetation ................................................................................................. 29

4.3 MODEL VERIFICATION ........................................................................................... 31

4.3.1 Field Program............................................................................................ 31

4.3.2 Comparisons with Model Predictions....................................................... 32

4.4 MODEL RESULTS – PRESENT CONDITIONS ............................................................. 36

4.4.1 Flow Conditions Near Deltaport............................................................... 36

4.4.2 Drainage Channels .................................................................................... 49

4.5 MODEL RESULTS – DELTAPORT THIRD BERTH PROJECT IMPACTS......................... 52

5.0 CONCLUSIONS ............................................................................................................. 56

6.0 REFERENCES................................................................................................................ 57

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Coastal Geomorphology Study – Appendix B - v - November 2004

List of Tables

Table B2-1: Results of Calibration – Comparison.......................................................................... 9

Table B2-2: Results of Calibration – Differences........................................................................... 9

Table B3-1: Tide Stations in Base Model..................................................................................... 16

List of Figures

Figure B1-1: Study Area Extent .................................................................................................... 1

Figure B1-1: General Project Layout............................................................................................. 2

Figure B1-3: Wide Area Model (a), Base Model (b) and Detailed Model (c) Areas of Interest .... 4

Figure B2-1: Extent of Tide2D Wide Area Model ......................................................................... 7

Figure B2-2: Variation of M2 Constituent Amplitude and Phase ................................................ 11

Figure B2-3: Comparison of Tide2D Predicted Water Levels at Sandheads ............................... 11

Figure B3-1: Extent of Base Model .............................................................................................. 14

Figure B3-2: Bathymetry Near Roberts Bank .............................................................................. 15

Figure B3-3: Base Model Computational Mesh in Area of Interest............................................. 15

Figure B3-4: Comparison of Predicted and Published Water Levels at Tide Gauges.................. 17

Figure B3-5: Comparison of Predicted and Observed Velocities near Roberts Bank for

Period February 23 to 24, 1984..............................................................................17

Figure B3-6: Representative Tidal Cycles.................................................................................... 18

Figure B3-7: Sensitivity Analysis – Fraser River Global Impacts ............................................... 20

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Coastal Geomorphology Study – Appendix B - vi - November 2004

Figure B3-8: Sensitivity Analysis – Fraser River Local Impacts ................................................. 21

Figure B3-9: Impact of Roughness Variation on Model Results.................................................. 22

Figure B3-10: December Ebb Tide - Existing Conditions............................................................ 23

Figure B3-11: December Flood Tide - Existing Conditions......................................................... 23

Figure B3-12: Model Results - Existing Conditions vs. Proposed Third Berth Project ............... 25

Figure B3-13: Impact Zone from Terminal 2 Alternative W2 ..................................................... 26

Figure B4-1: Detailed Model Extent and Mesh............................................................................ 28

Figure B4-2: Detailed Model Bathymetry .................................................................................... 30

Figure B4-3: Spatial Extent of Modelled Eelgrass ....................................................................... 31

Figure B4-4: Location of ADCP Current Measurements ............................................................. 33

Figure B4-5: Comparison Locations for Modelled and Measured Velocities.............................. 33

Figure B4-6: Comparison of Predicted and Measured Velocity in Trunk Drainage

Channel for Comparison Location 1......................................................................34

Figure B4-7: Comparison of Predicted and Measured Velocity in Ship Turning Basin for

a) Comparison Location 2, and b) Comparison Location 3...................................35

Figure B4-8: Flow Patterns during Neap Tidal Cycle (a) – February 8, 2003 ............................. 37

Figure B4-9: Flow Patterns during Neap Tidal Cycle (b) – February 8, 2003 ............................. 38

Figure B4-10: Flow Patterns during Neap Tidal Cycle (c) – February 8, 2003 ........................... 39

Figure B4-11: Flow Patterns during Neap Tidal Cycle (d) – February 8, 2003 ........................... 40

Figure B4-12: Flow Patterns during Mean Tidal Cycle (a) – May 3, 2003.................................. 41

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Coastal Geomorphology Study – Appendix B - vii - November 2004

Figure B4-13: Flow Patterns during Mean Tidal Cycle (b) – May 3, 2003.................................. 42

Figure B4-14: Flow Patterns during Mean Tidal Cycle (c) – May 3, 2003.................................. 43

Figure B4-15: Flow Patterns during Mean Tidal Cycle (d) – May 3, 2003.................................. 44

Figure B4-16: Flow Patterns during Large Tidal Cycle (a) – December 27, 2003 ...................... 45

Figure B4-17: Flow Patterns during Large Tidal Cycle (b) – December 27, 2003 ...................... 46

Figure B4-18: Flow Patterns during Large Tidal Cycle (c) – December 27, 2003 ...................... 47

Figure B4-19: Flow Patterns during Large Tidal Cycle (d) – December 27, 2003 ...................... 48

Figure B4-20: Flow Patterns during Ebb Tide Near the Head of the Largest Tidal Channel....... 50

Figure B4-21: Flow Patterns during Flood Tide Near the Head of the Largest Tidal Channel.... 51

Figure B4-22: Effect of Deltaport Third Berth Project on Flow Patterns – Neap Tide................ 53

Figure B4-23: Effect of Deltaport Third Berth Project on Flow Patterns – Mean Tide ............... 54

Figure B4-24: Effect of Deltaport Third Berth Project on Flow Patterns – High Tide ................ 55

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Coastal Geomorphology Study – Appendix B - 1 - November 2004

1.0 INTRODUCTION

1.1 SCOPE OF WORK

This report is included as Appendix B of the DRAFT Coastal Geomorphology Study (Northwest

Hydraulic Consultants and Triton Consultants Ltd., 2004). It is intended to provide background,

and in-depth information to support the draft report of the Coastal Geomorphology Study

concerning the Deltaport Third Berth Project. This appendix summarizes the development,

calibration and verification of a suite of two-dimensional hydrodynamic models that were used

to assess impacts of the proposed Deltaport Third Berth Project at Roberts Bank. The terms of

reference for the study identified the area of interest to be modelled as follows: “Extending north

to the mouth of the main arm near Steveston, south to Point Roberts, west to the 100 m depth

contour and east to the highwater mark”. Figure B1-1 shows the area of interest and the

surrounding features.

Figure B1-1: Study Area Extent


1.2 DELTAPORT THIRD BERTH PROJECT DESCRIPTION

Figure B1-2 shows the general layout of the proposed Deltaport Third Berth Project. The main

components relevant to the geomorphic investigations consist of (1) a wharf to accommodate the

third berth, (2) a container storage yard constructed of dredged fill, (3) a tug basin and boat

launch, and (3) an extension to the ship channel. The wharf is 427 m long and may consist either

of a pile and deck structure or a caisson structure. The berth will be dredged to a depth of 16 m

(chart datum) with the top of the deck at 8.0 m.

Figure B1-1: General Project Layout

Approximately 20 ha of new land will be constructed to provide the container storage yard. The

land will be created through dredging and landfill operations. Revetment works along the north

side of the fill will consist of rock riprap.

The existing tug moorage area on the northeast corner of Deltaport will be re-located to the north

corner of the Third Berth. The tug moorage area will consist of a floating dock, walkway and

dredged basin. The tug moorage area will be dredged to a depth of 6.5 m.

Estimates of dredge cut and fill volumes are preliminary at this time and indicate 1.6 million m3

of material will have to be excavated for the ship channel and an additional 2.0 million m3 is


required for constructing the Third Berth and terminal area. It is estimated that up to

2.3 million m3 of the total dredged volume will be unsuitable for site fill. Details of the dredge

spoil disposal plan are not available at this time.

1.3 TERMINAL 2 PROJECT

Preliminary layouts for Terminal 2 were provided by VPA to assess potential interactions and

cumulative effects with the Deltaport Third Berth Project. Several different configurations were

considered during the course of the investigations. The most recent alternative that has been

assessed at this stage is termed W2-Alternative 5 (Figure B1-2). This alternative included

additional facilities extending 600 m northwest of the existing terminal with an adjacent

300 to 600 m wide basin dredged to 16.0 m.

1.4 METHOD OF APPROACH

Hydrodynamic modelling was conducted in three phases, as illustrated in Figure B1-3. The first

phase involved tidal modelling studies in the Strait of Georgia, Juan de Fuca Strait and around

Vancouver Island using Triton Consultants Tide2D model. This “Wide Area Model” is described

in more detail in Section 2. The objective of this work was to provide tidal height and tidal

current boundary conditions along a line in the deeper waters of Strait of Georgia parallel to

Roberts Bank extending from just north of Sandheads at the mouth of the Fraser River to the

southern tip of Point Roberts. These boundary conditions were used primarily to drive other

detailed tidal models of the Roberts Bank inter-causeway area.

The second phase consisted of developing a relatively coarse grid hydrodynamic model

encompassing the entire area of interest, including portions of the Strait of Georgia and the

Fraser River. This model, referred to as the “Base Model”, is described in Section 3.0. The Base

model was used to assess current patterns and water circulation in the Fraser estuary and on the

Roberts Bank tidal flats. This involved simulating the effects of varying tide levels and Fraser

River discharges in the area of interest. The base model was also used as a diagnostic tool to

identify the extent of potential impacts from the proposed alternative developments. A critical

zone for detailed, hydrodynamic and morphologic modelling was defined using these

preliminary results.


Figure B1-3: Wide Area Model (a), Base Model (b) and Detailed Model (c) Areas of Interest

The third phase of the river and tidal current modelling involved the development of a more

detailed model to investigate potential local project impacts within the inter-causeway area of the

tidal flats and around local structures near the Deltaport Third Berth Project. One of the main

features of this “Detailed Model” was its capability to model wetting and drying by simulating

the transition from surface to sub-surface flow over the tidal flats and representing local effects

of eelgrass on roughness. The Detailed Model is described in Section 4.0 of this appendix. The

Detailed Model was driven by boundary conditions supplied from the Base Model. This

approach allowed us to represent critical areas of interest with a high degree of resolution (5 m),

while maintaining a reasonable mesh size and computational time.

1.5 ASSUMPTIONS AND LIMITATIONS

Two-dimensional numerical models compute depth-averaged velocities over a two-dimensional

mesh or grid. The models cannot represent stratified flow or highly three-dimensional flow with

vertical velocity components. Stratified flow is important in the main channel of the Fraser River

estuary where a salt-wedge forms, but is less significant on Roberts Bank where the flow is

generally well mixed. Furthermore, three-dimensional secondary currents are most strongly

developed in deep bends or near training walls such as in the main arm of the Fraser River at

Steveston Bend, and generally not on shallow tidal flats. Therefore, a two-dimensional model is

appropriate for assessing the kinds of hydrodynamic processes occurring in the area of interest.


The sediment dynamics on the Fraser River delta and adjacent tidal flats are complicated. A

recent comprehensive review of hydrodynamic and sediment transport modelling of shallow-

water estuaries, lakes and lagoons (Teeter et al., 2001) concluded that available numerical

modelling techniques are limited by present computational power as well as our understanding of

the interactions between hydrodynamics, sediment and vegetation (such as eelgrass). Therefore,

a range of methods have been used to supplement the numerical modelling results, including

direct field measurements, historical geomorphic investigations and analytical computations.

However, the models provide a very powerful tool for assessing and comparing “With Project”

and “Without Project” conditions in the area of interest.


2.0 WIDE AREA MODEL

2.1 MODEL DESCRIPTION

The wide area model encompasses all tidal waters surrounding Vancouver Island and is driven

by ocean boundary conditions in the eastern Pacific Ocean. The numerical model used for this

work was Tide2D (Walters, 1987), a two-dimensional finite element harmonic model that has

been applied successfully by Triton Consultants Ltd to more than 30 tidal systems worldwide

over the last ten years. Although Tide2D does not specifically handle wetting and drying of tidal

flats, it provides useful results in those areas where the water depth is more than about 1 m at

mean water level. At Roberts Bank this corresponds to a chart depth of +2.0 m (mean sea level is

+3.0 m CD), which includes the majority of the area of the tidal flats, in particular the large

eelgrass beds. Preliminary investigations with Tide2D were therefore undertaken to evaluate the

impact that eelgrass has on seabed friction over the tidal currents.

Tide2D is a two-dimensional finite element harmonic model, which solves the non-linear,

shallow water equations for sea level, and depth averaged velocity using a finite element

discretization in space, and a harmonic expansion in time (Walters, 1987). Because the

governing equations are elliptic, there are no stability criteria such as associated with hyperbolic

time-stepping methods. The numerical solution applies harmonic decomposition of the

governing shallow water equations and solves the equations in the frequency domain rather than

using time-stepping procedures. This technique is exceptionally computationally efficient and is

particularly suited to modeling tidal motions where the number of frequencies is small in number

or for modeling steady state forcing mechanisms such as quasi-stationary wind/pressure systems

or river flow. Tide2D has two major limitations: neither drying flats, nor non-steady or non-

harmonic forcing conditions can be modeled.

2.2 MODEL DEVELOPMENT

Figure B2-1 shows the extent of the Tide2D wide area model. The finite element numerical

model grid was based on model Vig6, originally developed by the Institute of Ocean Sciences

(IOS), Pat Bay, B.C. (Dr. Michael Foreman) during the 1990s. This grid has been improved by


Figure B2-1: Extent of Tide2D Wide Area Model

Triton in the processes of doing projects for IOS and other clients such as B.C. Hydro. For this

Vancouver Port Authority (VPA) Project, Triton has added very significant grid detail in the area

of Roberts Bank itself along with detail from Triton’s own Fraser River numerical model.

Digital sources of bathymetric data in the area of Roberts Bank were obtained from the Canadian

Hydrographic Service (via Nautical Data International, St John’s, NF) and VPA. The model grid

in the immediate project area has approximately 25 m or less spacing between calculation points.

This compares with many 1000’s of metres in the open Pacific Ocean. Such a large variation in

discretization is possible only within a finite-element modeling framework; the only limitation is

that finite element size must increase (or decrease) in size smoothly, and not too quickly. This

criterion has been maintained within the model developed for this project.


Two model grids were developed for this project - one including the existing Roberts Bank

facilities and one for the proposed Delta Port Expansion (DPE). The DPE grid has 132,000

calculation nodes and 229,000 elements, this compares with the original IOS Vig6 with 68,000

nodes.

2.3 MODEL CALIBRATION

The latest Pacific Ocean tidal boundary conditions were provided by Michael Foreman at IOS.

These boundary conditions are based on the detailed interpretation of satellite data supplemented

by numerical modeling of tides in the Pacific Ocean. A total of eight tidal constituents were used

at the model-driving boundary - four semi-diurnal (M2, K2, N2 and S2) and four diurnal (K1,

O1, P1, Q1). The Tide2D model was calibrated against recorded tidal constituent data (CHS) at

Victoria, Patos Island (north end Boundary Pass), Tsawwassen, Sandheads, Point Atkinson,

Ladysmith, Texada Mines, and Mittlenatch Island. Principal calibration was done on the major

diurnal and semi-diurnal (twice daily) constituents K1 and M2 respectively.

Model bottom friction was adjusted in six principal areas:

• Juan de Fuca Strait;

• Boundary Pass (southern Gulf Islands);

• “Okiloso” Island Group (north end of Strait of Georgia);

• Seymour Narrows/Discovery Passage; and

• Malcolm Island Region (north end of Johnstone Strait).

In addition to friction adjustments in these areas of large flows and high currents, enhanced

friction was applied to eelgrass areas identified in the Roberts Bank area. This additional eelgrass

friction is indicative only of the impact of this plant on tidal flow, as no measured current data is

presently available for model calibration.

Table B2-1 and Table B2-2 show the “best” calibration data set obtained during these modeling

studies.


The model calibration is considered to be good, especially in the area of interest in the Southern

Strait of Georgia. Modeled tidal amplitudes are typically within about 5%, or better, of the

measured data, and modeled tidal phase is typically within 5 degrees (10 minutes M2, 20

minutes K1) of measured data.

Table B2-1: Results of Calibration – Comparison

Amp Phase Amp Phase Amp Phase Amp Phasem degrees m degrees m degrees m degrees

Victoria 0.37 317.8 0.63 269.7 0.41 299.7 0.62 270.1Patos Island 0.68 25.0 0.79 285.6 0.69 28.3 0.84 288.0Tsawwassen 0.82 27.8 0.85 284.5 0.83 32.6 0.88 289.5Sandheads 0.87 30.9 0.84 286.5 0.91 35.5 0.91 290.5Point Atkin 0.92 31.2 0.86 286.1 0.94 36.2 0.92 290.9Ladysmith 0.71 16.3 0.80 281.8 0.74 27.6 0.84 289.3Texada Min 0.99 43.2 0.90 286.8 1.04 38.9 0.95 291.8Mittlenatch 0.99 34.5 0.86 289.2 1.05 39.9 0.96 292.1

M2 Constituent K1 Constituent M2 Constituent K1 ConstituentMeasured Tidal Data Model Tidal Data

Table B2-2: Results of Calibration – Differences

Amp Phase Amp Phasem degrees m degrees

Victoria -0.04 18.10 0.01 -0.40Patos Island -0.01 -3.26 -0.05 -2.40Tsawwassen -0.01 -4.83 -0.04 -4.97Sandheads -0.05 -4.55 -0.07 -4.02Point Atkin -0.03 -4.96 -0.06 -4.76Ladysmith -0.03 -11.32 -0.04 -7.49Texada Min -0.05 4.32 -0.05 -5.00Mittlenatch -0.06 -5.37 -0.10 -2.89

M2 Constituent K1 ConstituentMeasured-Model

However, within this generally excellent calibration, Victoria is poorly defined in phase (M2)

and Ladysmith clearly also needs more work in phase (M2 and K1). The M2 phase results for

Victoria are not surprising as Victoria is located close to an M2 amphidromic point where tidal

ranges are small and phase varies very rapidly over relatively short distances. The results for

Ladysmith could certainly be improved by further investigation of the flows through the eastern


Gulf Islands passes (e.g., Active Pass). Any improvements in this model area would not be

expected to significantly change the results in the southern Strait of Georgia.

2.4 MODEL RESULTS

The model results for the tidal constituent M2 in the southern Strait of Georgia are illustrated in

Figure B2-2. The flooded contours are M2 amplitude (m) and the black contours are M2 phase

(degrees). Tidal phase is the timing of tide as it progresses through the Strait. For M2, one degree

represents about two minutes in time.

Similar results were developed for the remainder of the eight constituents used in the study.

Together, these eight constituents explain more than 95% of the total tidal signal in the southern

Strait of Georgia.

Tidal constituent data for the eight modelled constituents were extracted from the Tide2D model

results at 91 locations along a line in the deeper waters of the Strait of Georgia parallel to

Roberts Bank. This boundary extended from just north of Sandheads at the mouth of the Fraser

River to the southern tip of Point Roberts. Tidal height data for the year 2003 (at 15 min

intervals) was synthesized from the eight tidal constituents, at each of the 91 locations. This data

was used as the outer boundary conditions for the detailed tidal flats numerical modelling

program.

Figure B2-3 shows a comparison between the predicted tidal height for the eight modelled

constituents in the Tide2D and a prediction based on the complete CHS recorded constituent data

set for Sandheads at the mouth of the Fraser River.


Figure B2-2: Variation of M2 Constituent Amplitude and Phase

0

1

2

3

4

5

6

Jan/29 Jan/30 Jan/31 Feb/01 Feb/02 Feb/03

Date (2003)

Tide

(m C

D)

Predictions based on Tide2D results with eight constituentsPredictions based on full CHS constituent database

Figure B2-3: Comparison of Tide2D Predicted Water Levels at Sandheads


3.0 BASE MODEL

3.1 MODEL DESCRIPTION

The Surfacewater Modelling System (SMS 8.0) program was used to develop the Base Model.

This package utilizes the US Army Corps of Engineers’ two-dimensional finite element

hydrodynamic and advection-dispersion models, including RMA2, SED-2D and ADCIRC.

After a period of initial model testing it was decided to utilize the ADCIRC program in SMS as

the Base Model. ADCIRC is the Advanced Circulation model for ocean, coastal areas and

estuaries developed by Dr. Rick Luettich at the University of North Carolina at Chapel Hill and

Dr. Joannes Westerlink at the University of Notre Dame. The model has been developed for the

U.S. Army and Navy over the last 15 years to compute circulation in coastal oceans associated

with tides, winds and density-driven flows (Luettich et al., 1991). ADCIRC is based on a

reformulation of the shallow water equations and applies a finite element discretization strategy,

which makes it free from spurious oscillations. The equations have been formulated using the

traditional hydrostatic pressure and Boussinesq approximations and have been discretized in

space using the finite element (FE) method and in time using the finite difference (FD) method.

The model permits application of highly unstructured grids with great detail specified locally.

ADCIRC’s basic formulation and algorithms have been extensively verified and have been

validated in tidal and wind-driven ocean, shelf and estuarine applications around the world

(Grenier et al., 1995; Hench et al., 1994; Westerink, 1993; Westerink et al., 1992). Recently the

model has incorporated methods for propagating flood waves over initially dry land, flood

recession over inundated regions and representation of barriers such as levees or jetties. Three

specific features that made it suitable for application to this study include:

• capability to model wetting and drying on the tidal flats

• capability to represent both tidal forcing and fresh water inflows from Fraser River

• capability to model structures such as dykes, culverts and other openings


3.2 BASE MODEL DEVELOPMENT

3.2.1 Work Carried Out

Development of the Base Model involved the following steps:

• obtaining tidal constituent boundary conditions;

• inputting topographic data to represent the area of interest;

• making a series of test runs to assess the stability and sensitivity of the model to various parameters such as roughness, eddy viscosity and time step interval;

• carrying out 30 day verification runs to confirm the model accuracy with local tidal data;

• repeating the runs with the proposed Deltaport Expansion layout;

• considering cumulative impacts associated with future VPA developments (a second terminal); and

• determining the spatial extent of local project impact on velocities and bed shear stresses within the area of interest.

3.2.2 Boundary Conditions

The boundaries adopted for the Base Model extend seaward into the Pacific Ocean and landward

up the Fraser River past Mission. The extent of the Base model is presented in Figure B3-1. The

model was driven by eight Le Provost tidal constituents (four semi-diurnal: M2, S2, N2, K1, and

four diurnal: O1, Q1, P1, K2) applied along the modelled ocean boundary. The Fraser River

inflow was set at a constant flow rate.


Figure B3-1: Extent of Base Model

3.2.3 Roberts Bank and Project Geometry

The Roberts Bank bathymetry required for numerical modelling was derived from information

provided by Triton and the VPA. Although the Base Model extends well into the Pacific Ocean

and up the Fraser River, the region of interest includes a 23 km long reach of Roberts Bank,

beginning at Steveston Bend and extending to Point Roberts. The existing Roberts Bank

bathymetry is illustrated in Figure B3-2.

Once the model extents were defined a computational mesh was generated by defining the spatial

and hydraulic characteristics of the bank as a series of nodes and elements. Node spacing ranges

from 100 to 45,000 m. The computational mesh in the area of interest is shown in Figure B3-3.


Figure B3-2: Bathymetry Near Roberts Bank

Figure B3-3: Base Model Computational Mesh in Area of Interest


3.2.4 Model Verification

The results from the Base Model were compared to tide levels predicted by Tide2D. In addition,

comparisons were made with published tide data supplied by the Department of Fisheries and

Oceans, Canadian Hydrographic Service tidal stations. These stations are listed below in

Table B3-1.

Table B3-1: Tide Stations in Base Model

Station Name

7590 Tsawassen7020 Sooke 7120 Victoria7330 Fulford Harbour7795 Point Aktinson7938 Northwest Bay7985 Comox

Figure B3-4 summarizes these comparisons and shows that the model predictions agree closely

with the published information.

The predicted velocities were also compared to field data recorded by two current meters located

immediately west of the Deltaport Terminal. Variance between predicted and the measured

velocities is expected for the following reasons:

• measurements were point velocities at the ocean floor while modelled predictions were depth-averaged,

• measured velocities could be affected by local wind conditions if taken in shallow water (i.e. measurements taken at -123.16 E, 49.123 N),

• measured velocities were obtained 20 to 27 years ago, while model is based on existing terminal and bed geometry.

The results for the period February 23 to 27, 1984 are summarized in Figure B3-5.


Figure B3-4: Comparison of Predicted and Published Water Levels at Tide Gauges

Figure B3-5: Comparison of Predicted and Observed Velocities near Roberts Bank for Period

February 23 to 24, 1984

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

4753800 4840200 4926600 5013000 5099400Time (s)

Velo

city

(m/s

)

-120

-60

0

60

120

180

240

300

360

Dire

ctio

n (d

eg fr

om N

)

Predicted Vel Measured Vel Predicted Dir Measured Dir


3.2.5 Representative Tide Conditions

The 2D numerical models developed for this study required a significant amount of real-time

computational effort to compute the dynamic conditions along Roberts Bank. Modeling over

long periods, weeks or months, would have significantly extended the time for each model run

and subsequently extended the length of the study. Three representative tidal cycles were

identified in order to subdivide the project into manageable time frames. The three time periods

and tidal cycles are presented in Figure B3-6 and include:

• Neap Tide – February 6 to 8, 2003

• Mean Tide – May 1 to 3, 2003

• High Tide – December 25 to 27, 2003

Additional tidal cycles were modelled, as required, to calibrate and verify the model results

against field-measured data collected from various sources.

Figure B3-6: Representative Tidal Cycles

0

1

2

3

4

5

0 12 24 36 48 60 72

Time (hr)

Wat

er S

urfa

ce E

leva

tion

(m c

hart

dat

um)

Mean Neap High


3.2.6 Sensitivity Analysis

A series of three model runs were conducted to determine the extent of the impact that varying Fraser River flows might have in the vicinity of Deltaport. The flows considered include a high freshet flood of 9,000 m3/s, a low freshet flood of 4,200 m3/s, and a condition where the Fraser River was not contributing discharge to the system. The third condition is unrealistic and was considered only to envelope the sensitivity analysis. Figures B3-7 and B3-8 illustrate the velocity distribution for these Fraser River discharges.

Increasing the Fraser River flow has little effect on velocities in the study area during high flood tides. However, during ebb tides the higher river flows result in higher velocities at the mouth of the river. The high velocities extend out towards the north end of Tsawwassen Terminal with the terminal and its causeway shielding any Fraser River effects from the inter-causeway tidal flats south of the terminal.

Uniform roughness changes have little effect on the tidal flow patterns. However, spatial variations in roughness significantly affect the flow. A uniform roughness (corresponding to a Manning’s n of 0.02) was applied to the entire model. A localized increase in roughness (corresponding to a Manning’s n of 0.07) was applied to the areas where dense eelgrass was mapped. The variation in roughness further concentrates flow down the main intertidal channel east of the south turn basin. Figure B3-9 illustrates the velocity distribution for uniform and spatially varying roughness.

3.3 MODEL RESULTS

3.3.1 Present Conditions

Figures B3-10 and B3-11 illustrate tidal patterns on Roberts Bank. Velocities are low within the study area throughout the tidal cycle (near the terminal and between the causeways), with maximum velocities below 0.7 m/s. Flow remains aligned with the causeways except during the slack-water tidal peaks when flow switches from ebb to flood or flood to ebb. The highest velocities in the inter-causeway area are found along the main intertidal channel east of the south turn basin, and along the edges of the causeways. Eelgrass (modelled with increased roughness) and the presence of defined intertidal channels tend to concentrate flow in these regions. The Detailed Model provides increased detail within the inter-causeway area.


Figu

re B

3-7:

Sen

sitiv

ity A

naly

sis –

Fra

ser

Riv

er G

loba

l Im

pact

s


Figu

re B

3-8:

Sen

sitiv

ity A

naly

sis –

Fra

ser

Riv

er L

ocal

Impa

cts


Figu

re B

3-9:

Impa

ct o

f Rou

ghne

ss V

aria

tion

on M

odel

Res

ults


Figure B3-10: December Ebb Tide - Existing Conditions

Figure B3-11: December Flood Tide - Existing Conditions


3.3.2 Third Berth Project

The model of the proposed Third Berth Deltaport expansion produced similar results to those

from the existing conditions model. Velocities are low in the study area, with little detectable

change in magnitude or direction. Impacts from Third Berth were limited to the local loss of flow

within the Third Berth footprint and around the Third Berth’s immediate boundary. Figure B3-12

illustrates the lack of any significant impact of the Third Berth during typical high tide

(December 25th, 2003 ebb and flood tide).

From the Base Model results, it is expected that no impacts from the Third Berth project will

occur outside of the low velocity area bounded by the inter-causeway area. The limited impacts

within the inter-causeway area will be illustrated in more detail by the Detailed Model.

3.3.3 Terminal 2 Project

Figure B3-13 illustrates the effects of the Terminal 2 W2-Alternative 5 option. Significant

changes to the velocity distribution are detected from model results along the upper tidal flats

northwest of the causeway and seaward of the west corner of the existing terminal. Future model

element densification in this area will refine the results seen in this area. Based on the model

results, no impacts to flow patterns or intensities are expected within the inter-causeway area or

in the vicinity of the Third Berth expansion project. Therefore the proposed Third Berth and

W2-Alternative 5 expansion projects can be modelled independently, with detailed study in the

vicinity of the W2-Alternative 5 not required for a study of the proposed Third Berth project.


Figu

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3-12

: Mod

el R

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ts -

Exi

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ondi

tions

vs.

Prop

osed

Thi

rd B

erth

Pro

ject


Figu

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3-13

: Im

pact

Zon

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2 A

ltern

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e W

2

Documents

ROBERTS BANK CONTAINER EXPANSION COASTAL …...two-dimensional hydrodynamic models for assessing project impacts associated with the Deltaport Third Berth Project. The terms of reference