Vancouver Port Authority Northwest Hydraulic Consultants Ltd.
/Triton Consultants Ltd. Roberts Bank Container Expansion File:
33863 Coastal Geomorphology Study - 27 - November 2004
channel, which remains in some form today. In general, the tidal
flow direction has been shifted
from a northwest to southeast trending direction towards Canoe
Passage, to a north-south
direction, parallel to the causeways but modified due to local
topographic controls.
Figure 3-7 illustrates topographic changes between 1968 and 2002
on the west side of Roberts Bank Causeway. These changes were
determined by comparing available bathymetric surveys (Appendix C).
The comparisons are limited by the accuracy of the available
surveys and must be judged as approximate only. Apparent
aggradation of 0.5 to 1.0 m is evident near the mouth of Canoe
Passage. Apparent degradation is evident along the edge of the fore
slope, which is consistent with the previous findings of Stewart
and Tassone (1989). Bed level changes on the western tidal flats
appear to have been minimal, at least within the expected accuracy
of the available surveys.
3.3.2 Inter-causeway Area
Figures 3-8 through 3-10 illustrate some of the morphologic
changes that have occurred in the
inter-causeway area between 1970 and 2002. Additional
information on historical changes is
contained in Triton (1996) as well as in Appendix C. The most
notable developments relate to
the initiation and growth of a network of tidal drainage
channels. This channel network did not
exist prior to port development. Channel formation was initiated
following the construction of
the Roberts Bank terminal and the dredging of the initial pit in
1969. Figure 3-8 shows Roberts
Bank in 1970, one year after completion of the coal port
causeway and in 1979. The channels
reached a moderate size by 1979. These initial drainage channels
were largely obliterated or
significantly modified when the larger ship-turning basin and
crest protection structure were
completed in 1982.
Figure 3-11 illustrates the growth of the two largest trunk
channels during this time. Figure 3-12
summarizes the changes in the extent and distribution of
eelgrass over the same period. These
plots are based on the mapping information in Triton (1996) and
the updated mapping carried out
by FREMP in 2003.
By 1989 four major points of outflow across the crest protection
structure had developed, fed by
channels ranging from between 100 m to 900 m in length. These
channels are numbered 1
through 4 in Figure 3-11. The two largest of the channels show
channel patterns that are quite
