8.0 PROJECT IMPACTS FROM DELTAPORT EXPANSION

Vancouver Port Authority Northwest Hydraulic Consultants Ltd. /Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Coastal Geomorphology Study - 95 - November 2004

8.0 PROJECT IMPACTS FROM DELTAPORT EXPANSION

8.1 GENERAL APPROACH

The main features of the Deltaport Third Berth Project are described in Section 1.4. The general

plan and layout of the project is based on Hemmera (2003) and drawings provided by VPA.

Based on the experience and knowledge gained from earlier port developments on Roberts Bank,

the following potential physical impacts were considered:

• potential triggering of new dendritic drainage channels and erosion of eelgrass on the tidal flats;

• potential local erosion or scour adjacent to new structures;

• potential impacts to overall delta stability caused by interruption of sediment transport; and

• changes to deposition patterns in dredged basins and adjacent areas.

However, given the relatively small scale of the proposed development in comparison to

previous works, it was recognized that potential impacts were likely to be more localized in

extent. This meant that the analysis required a relatively fine resolution in order to detect

impacts.

The assessment of morphologic response is based on two different approaches. First, the

numerical wave models and hydrodynamic models were used to generate representative

hydrodynamic simulations of “With Project” and “Without Project” conditions. The difference

between “With Project” and “Without Project” velocities and bed shear stresses were then

mapped to represent the zone of potential impacts. Additional sediment transport computations

were then made to further assess the effect of these hydraulic changes on sediment movement

patterns.

Second, additional interpretative geomorphic assessments were made independently of the

numerical modeling. These interpretive studies rely primarily on the experience gained from

earlier developments at the Ferry Terminal and Roberts Bank, as well as the extensive field

observations that were made during the investigation (Appendix C). The main focus of this work


is to identify the potential for new drainage channels to develop in response to the extension and

dredging work planned at Deltaport.

8.2 IMPACTS ON WAVES

Figures 4-2 through 4-4 show representative examples of wave transformations on Roberts Bank

under present conditions. Additional plots were made with the proposed Deltaport Third Berth

project in-place. The projected impact of the project on the wave heights in the study area is very

small and is difficult to even detect from visual examination of the two sets of plots. Therefore,

output from the two sets were compared by computing the changes between the “With Project”

and “Without Project” conditions at each point in the model grid. Two parameters were used to

represent the project impacts: a) changes in bottom velocity, expressed by U1-U0, and b) changes

in the sediment mobility, expressed by T1-T0. The comparisons were made for the conditions

listed in Table 4-1. Figure 8-1 illustrates the impacts on waves from the southeast at low,

medium and high points of a Mean Tide, in terms of the change in velocity and the change in

mobility. Figure 8-2 illustrates the same impacts on waves from the south. These directions were

selected for display since they produced the greatest overall impacts. However, in all cases, the

impact zone was very localized, being limited virtually to the footprint of the main structures.

The wave height was increased directly in front of the wharf extension. The wave height was

reduced directly behind the wharf and along the side of the causeway directly behind the wharf

extension due to sheltering. No significant changes occurred in the vicinity of the drainage

channels or on the upper portions of the tidal flats.

8.3 IMPACTS ON TIDAL CURRENTS

The “With Project” bathymetry was digitized and was used to generate a new computational

mesh for the inter-causeway area. The new wharf was also added as a no-flow boundary. The

model was then re-run for a range of different tide conditions. Initial review of the model output

showed that the impacts of Deltaport expansion were very localized, and essentially confined to

the immediate flow field around the modified structures and the dredged channel. It was also

found that the absolute magnitude of the changes was very small. Therefore, in order to illustrate

these changes graphically, we have prepared detailed comparisons of the local area around the


Figu

re 8

-1: I

mpa

cts

of D

elta

port

Exp

ansi

on o

n W

ave

Indu

ced

Vel

ocity

and

Mob

ility

Fac

tor,

SE W

aves

at a

Low

Tid

e, M

ean

Tid

e an

d H

igh

Tid

e


Figu

re 8

-2: I

mpa

cts

of D

elta

port

Exp

ansi

on o

n W

ave

Indu

ced

Vel

ocity

and

Mob

ility

Fac

tor,

S W

aves

at a

Low

Tid

e, M

ean

Tid

e an

d H

igh

Tid

e


project site. Due to the large amount of output generated during the computer runs, it is not

practical to reproduce all of the results. The current patterns are illustrated for a representative

large tidal range during flood and ebb tide conditions in Figures 8-3 and 8-4. Figures 8-5 and 8-

6 show similar results for a representative mean tidal range. Additional plots for different tidal

ranges and times are provided in Appendix B.

The plots show that the end of the present wharf extends into the flow, inducing a zone of flow

divergence and a re-circulating eddy behind it during flood tides (Figures 8-3 and 8-5).

Extending the wharf further simply displaces this flow pattern landward but does not appear to

significantly change the overall pattern. During the ebb tide, the wharf causes the flow to

accelerate around its end, creating a zone of local flow concentration (Figures 8-4 and 8-6).

Extension of the wharf creates higher flow concentration at the end of the structure. However,

the absolute magnitude of the peak velocities remains very low and is typically less than 0.1 m/s.

These results indicate that the primary impact of the proposed Deltaport expansion will be to

effectively shift the existing flow patterns shoreward.

Figure 8-7 shows the differences between “With Project” and “Without Project” tidal current

velocities during a mean tide. Results for other tide conditions are presented in Appendix B. The

velocity differences were computed at each node in the computational mesh. These values were

then plotted and contoured to illustrate the spatial extent of the project impacts. Velocity

differences of less than 0.05 m/s were considered to be insignificant as they are within the

tolerance of the numerical model computations. These figures show that the impacts were highly

localized and so small as to be near the tolerance of the numerical computations. (Some apparent

velocity differences far from the project site are clearly induced by numerical imprecision rather

than actual project impacts).

8.4 IMPACTS ON SEDIMENT TRANSPORT

The magnitude of the wave bottom velocities and tidal current velocities in the vicinity of the

proposed expansion area are well below the threshold for significant sediment transport of fine


Figu

re 8

-3: I

mpa

cts o

f Del

tapo

rt o

n Fl

ow V

eloc

ities

dur

ing

a L

arge

Tid

al C

ycle

, Flo

od T

ide


Figu

re 8

-4: I

mpa

cts o

f Del

tapo

rt o

n Fl

ow V

eloc

ities

dur

ing

a L

arge

Tid

al C

ycle

, Ebb

Tid

e


Figu

re 8

-5: I

mpa

cts o

f Del

tapo

rt o

n Fl

ow V

eloc

ities

dur

ing

a M

ean

Tid

al C

ycle

, Flo

od T

ide


Figu

re 8

-6: I

mpa

cts o

f Del

tapo

rt o

n Fl

ow V

eloc

ities

dur

ing

a M

ean

Tid

al C

ycle

, Ebb

Tid

e


Figu

re 8

-7: E

ffec

t of D

elta

port

Thi

rd B

erth

Pro

ject

on

Flow

Pat

tern

s – M

ean

Tid

e


sand. Therefore, we do not expect significant alterations in sediment transport patterns to occur

as a result of Deltaport expansion. Furthermore, no significant local scour or infilling is

anticipated adjacent to the wharf, navigation channel or in the tug basin.

8.5 IMPACTS ON TIDAL DRAINAGE CHANNELS

Figure 8-8 shows two profiles through the proposed excavations for the Deltaport Third Berth

Project. The main excavation involves deepening the approach channel to the wharf extension.

This excavation occurs in deep water where the existing ground level is -12 m CD. Based on our

understanding of past tidal channel formation on Roberts Bank, there is no potential for

significant headcutting to occur from this excavation. Furthermore, due to the large depths, the

peak velocities generated by tidal currents in this area are very low; typically less than 0.2 m/s.

Therefore, the risk of any significant new channel formation occurring from the new excavation

appears to be negligible.

Preliminary plans show the tug basin extending into the existing crest protection. In this area the

crest protection is at ground level and does not project above the tidal flats. Some modification to

the structure is anticipated, although details of this feature are not finalized at this time.

Excavation of the tug basin may involve cutting into portions of the tidal flats that are above

LLW. Theoretically, therefore, there is some potential for minor headcutting to be initiated in

this area, particularly if the crest protection was eliminated. However, given the very limited

extent of the excavation and its orientation with respect to the existing drainage patterns, the

potential for headcutting is expected to be minor. Furthermore, this effect should be controlled if

the crest protection structure is modified to tie-in with the tug basin.

8.6 INTERACTION BETWEEN DELTAPORT THIRD BERTH AND TERMINAL 2 PROJECT

8.6.1 Preliminary Layout of Terminal 2

Terminal 2 will create a new three-berth container terminal on the west side of the causeway.

Only preliminary plans are available for this project at this time. The adopted configuration that

was assessed was provided by VPA and is identified as “W2-Alternative 5”. A schematic of this

layout is shown in Figure 1-2. The pod extent covers an area of approximately 95 ha and


the seaward edge is flush with the existing pod. A large dredged basin and navigation channel

extends out to the west and south west to provide access. Preliminary plans would require

substantial dredging into the western portion of the tidal flats. The excavation would extend to

approximately El. 1 m (CD). It was assumed that no mitigation measures were provided at the

site.

8.6.2 Effect on Waves

A complete series of wave refraction runs was made using the preliminary Terminal 2

configuration to determine if there was any risk of it causing additional impacts to the area

impacted by the Third Berth Project. The runs were made for the complete set of deep-water

wind and wave conditions listed in Table 4-1. Figures 8-9 and 8-10 illustrate representative

results for waves approaching from the northwest and west. These directions were chosen since

they represented the most severe for producing impacts at Deltaport. All of the comparisons

indicate that potential wave impacts from Terminal 2 would be localized on the west side of the

Causeway and would not extend into the inter-causeway area in the vicinity of Deltaport.

Therefore, any potential impacts from Terminal 2 should not interact with the localized wave

impacts associated with Deltaport expansion.

8.6.3 Effect on Tidal Currents

Figure 8-11 illustrates the effects of the proposed Terminal 2 on tidal current patterns. The

proposed new terminal is expected to induce significant changes to the velocity and flow patterns

on the west side of the causeway and upper portions of the tidal flats northwest of the causeway

and seaward of the west corner of the existing terminal. However, no impacts were detected

within the inter-causeway area or in the vicinity of the Third Berth project.

8.6.4 Assessment of Results

Terminal 2, as presently defined by VPA, is not expected to interact with, or modify the

hydraulic and morphologic impacts generated by the proposed Deltaport Third Berth project. In

terms of potential effects on waves, tidal current hydrodynamics and sedimentation, the Third

Berth Project and additional new development at Terminal 2 can be considered independently.


Figu

re 8

-9: I

mpa

ct o

f Ter

min

al 2

Pro

ject

on

Wav

e C

ondi

tions

, Vel

ociti

es, a

nd C

hang

e in

Mob

ility

dur

ing

a

NW

Win

d at

Low

Tid

e, M

ean

Tid

e an

d H

igh

Tid

e


Figu

re 8

-10:

Impa

ct o

f Ter

min

al 2

Pro

ject

on

Wav

e C

ondi

tions

, Vel

ociti

es, a

nd C

hang

e in

Mob

ility

dur

ing

a

W W

ind

at a

Low

Tid

e, M

ean

Tid

e an

d H

igh

Tid

e


Figu

re 8

-11:

Tid

al F

low

Pat

tern

Com

pari

son

– W

ith a

nd W

ithou

t Ter

min

al 2


9.0 CONCLUSIONS

Based on the combined analysis of the numerical modelling and geomorphic investigations, the

following conclusions have been reached with respect to the proposed Deltaport Third Berth and

Terminal 2 Projects:

1. Impacts of the proposed Deltaport Third Berth Project on tidal currents and waves will be

small and localized and essentially confined to the immediate flow field around the wharf

extension and the dredged channel. Tidal velocities will increase locally along the front

of the wharf extension, and decrease behind the wharf extension. The magnitude of the

velocities in the impact zone is well below the threshold for any significant sediment

transport. We do not expect any significant morphological impacts to develop in response

to changes in tidal flow magnitude or direction.

2. The end of the present wharf extends into the flow, which causes a zone of flow

divergence and a weak eddy to form behind the wharf during flood tides. Extending the

wharf simply shifts the flow pattern landward but does not appear to significantly change

the overall pattern. During the ebb tide, flow accelerates and concentrates at the end of

the wharf. Extending the wharf will create higher flow concentration at the end of the

structure; however, the absolute magnitude of the peak velocities remains very low and is

typically less then 0.1 m/s, which is very similar to the present situation.

3. The risk of new tidal drainage channels forming in response to planned navigation

dredging appears to be very low. The proposed channel excavation will occur in

relatively deep water (below LLW and the tidal flats where headcutting is initiated) and

will not induce significant headcutting on the tidal flats. There is some potential for

localized disturbance of the tidal flats near the proposed tug basin, which could induce

shallow, small-scale channels to form, although this can be controlled if the existing crest

protection structure is modified. Further design information on the tug basin and plans for

re-aligning the crest protection structure need to be reviewed and assessed.


4. Model simulations were made to assess potential cumulative effects the proposed

Terminal 2 Project could have on the Deltaport Third Berth Project. This analysis showed

the presently proposed Terminal 2 Project would not affect hydrodynamic or sediment

transport conditions in the vicinity of the Deltaport Third Berth Project. In terms of

potential effects on waves, tidal current hydrodynamics and sedimentation, the Third

Berth Project and Terminal 2 development can be considered independently.

5. Previous port developments on Roberts Bank induced long-term morphological changes

on the tidal flats, which are continuing to this day. The main physical changes involved

initial headcutting on the tidal flats, expansion of eelgrass beds and the formation of a

network of tidal drainage channels.

6. The large drainage channel in the middle of the inter-causeway area continues to expand

in both the seaward and landward directions. Sand from the trunk channel is being

transported up onto the tidal flats during flood tides to form a large sand lobe. It is

expected that the trunk channel will expand further shoreward before eventually

stabilizing. Shoreward expansion is limited by the higher ground elevation of the tidal

flats and the reduced amount of runoff that can be generated during the tidal exchange.

7. The crest protection structure appears to have effectively limited the growth of at least

two of the smaller channels. However, the large channel near the centre of the inter-

causeway area has partially by-passed the structure and continues to expand. This site, as

well as similar experience at the smaller structure near the B.C. Ferries terminal,

illustrates the difficulty of fully preventing channel formation when the contributing

drainage area leading to the channel is large. However, this situation will not arise at the

Third Berth Project.


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Documents

8.0 PROJECT IMPACTS FROM DELTAPORT EXPANSION