MEETING OF CONSULTANTS...Title: MEETING OF CONSULTANTS : Subject: MEETING OF CONSULTANTS : Keywords
Final-geomorph...Vancouver Port Authority Northwest Hydraulic Consultants Ltd. /Triton Consultants...
Transcript of Final-geomorph...Vancouver Port Authority Northwest Hydraulic Consultants Ltd. /Triton Consultants...
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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