Section 3.10: Site Plans and Technical Data - Rick Neufeld Comments

Northern Gateway Pipelines Inc.
Section 3.10: Site Plans and Technical Data
Table of Contents
Typically, the current speeds diminish with water depth. The historical data indicate subsurface currents
in the inland waterways at depths below 75 to 100 metres are typically 3 to 20 cm/s (0.1 to 0.4 knots) with
maximum speeds of 10 to 60 cm/s (0.2 to 1.2 knots) (Reference 10).
A more recent study conducted between Sept. 2005 and Jan. 2006 (Reference 8) deployed an Acoustic
Doppler Current Profiler (ADCP) unit in the manoeuvring area approximately 200 metres from shore at a
depth of 179 metres. The results from this study indicate average near surface current speeds of 8 cm/s
(0.15 knots) with a maximum near surface current speed of 51 cm/s (1.0 knot). The results also show a
pronounced decrease in current speeds with respect to depth. At a depth of 40 metres the average and
maximum current speeds are 3.4 cm/s (0.07 knots) and 24 cm/s (0.5 knots) respectively or approximately
half the near surface current speeds. At depths below 75 metres, current speeds are reduced even further.
Overall, the results of this recent study are consistent with the historical data.
As a further comparison with the historical data, the published tidal current velocities indicated on the
CHS Marine Chart No. 3743 for Douglas Channel are 0.5 knots for flood conditions and 1 knot for ebb
conditions.
In addition to tidal currents, wind-generated surface currents may develop as energy is transferred from
the wind to the water surface layer. In the open ocean, the current speed will be about 2 percent to 3
percent of the wind speed. For the 100-year return wind with a speed of 25.6 metres/s, a wind-generated
surface current of approximately 80 cm/s (1.5 knots) is estimated.
Due to the confined nature of the inland waterways, the currents typically flow in the direction of the
channel, with cross channel flow being minimal. The currents at the proposed marine terminal flow in a
NNE to SSW direction in alignment with the channel at this location.
3.4.2 Currents at Berth Locations
To determine the currents precisely at the berth locations an ADCP unit was deployed in 30 metres deep
water, at the fender line of the proposed berths, from January to April 2006 (Reference 9). The average
and maximum near surface currents speeds recorded at the berth locations were 10 cm/s (0.2 knots) and
66 cm/s (1.3 knots) respectively. The current speeds diminish with depth, with the average and maximum
values at a depth of 29 metres being measured as 3.3 cm/s (0.06 knots) and 21.0 cm/s (0.4 knots)
respectively. These results are in general agreement with those from the manoeuvring area.
Since the footprint of the marine structures is very small compared to the overall channel size, (the width
of the channel at the berth locations is approximately 2,700 metres wide), it is anticipated the proposed
marine structures will have no influence on overall tidal levels or overall currents. Even directly at the
berths, the effects on current velocities and directions should be minimal considering:
The berths and moored ships are aligned with the channel sides and direction of current flow;
Most marine structures are “open” structures providing little obstruction to current flow;
Dredging volumes are insignificant compared to the overall channel size and volume of water; and,
Significant underkeel clearance exists even under a fully loaded VLCC due to the steep bathymetry at the
terminal location, thereby reducing any shallow water effects with respect to deep draught vessels.
January 20, 2010 FINAL - Rev. 0 Page 3-7