Trans Mountain Pipeline (ULC)

Trans Mountain Expansion Project

Volume 8A

Volume 8A – Marine Transportation

Page 8A–67

Figure 2.1.4

10 Per Cent Under Keel Clearance Requirement

Since channel width varies with tidal height so then does the extent to which tankers can be

loaded. Occasionally, under the largest high tides, Aframax tankers can load up to about

90,000 tonnes (approximately 80 per cent DWT capacity) of cargo and based on the average

density of heavy crude oil loaded at Westridge Marine Terminal this is equivalent to about

98,000 m

3

(615,000 bbls). However, over the tidal cycle the average cargo loaded would be

about 550,000 bbls (equivalent to about 70 per cent DWT capacity). The effect of the draft

restrictions on cargo capacity were taken into consideration by Trans Mountain when estimating

the extent of tanker traffic that might result from the Project. This estimate was used in the

quantitative risk assessment (TERMPOL 3-15, Volume 8C-12) of an oil spill occurring from one

of these tankers.

2.2

Project-Related Changes to Marine Transportation and Traffic Volumes

2.2.1

Vessel Type and Marine Traffic Volume

As a result of the Project, marine traffic volume calling at the Westridge Marine Terminal will

increase. The types of vessels calling at the Westridge Marine Terminal (

i.e.

, barges, Panamax

and Aframax size tankers) will not change as a result of the Project. As well, the vessels calling

at the Westridge Marine Terminal after the Project is in operation will continue to use the

existing marine transportation routes depicted in Figure 1.3.1.

Source:

Obermeyer pers. comm.

Note:

This cross section represents the narrowest portion of the Second

Narrows MRA passage.

FIGURE 2.1.4

10 PER CENT UNDER KEEL

CLEARANCE REQUIREMENT