1) The study modifies the geometry of the Fraser River in a numerical ocean model to improve simulations of tides and the Fraser River plume. 2) Extending and deepening the river channel generated stronger cross-strait surface currents that better matched observations, and tidal amplitudes in the estuary corresponded well with measurements. 3) Reducing vertical mixing parameters, such as eddy viscosity and diffusivity, produced weaker along-strait flow and surface current patterns closer to drifter data, further improving the model results.

1. ImpactoftheFraserRiverGeometryonTidesandtheRiverPlumeinaModeloftheFraserRiverPlume
Data-Model Nowcast Result Comparisons to
Tidal Amplitudes in the Fraser River Estuary
Sensitivity Experiment on River Geometry
Reference
Data-Model New Results Comparisons
Model Configurations
Statistics of Various River Geometry and Parameters
Summary
Introduction
Background
- The Fraser River plume (Fig. 1) is the brackish layer of water formed by the Fraser
River discharge into the Strait of Gerogia (hereafter SoG) near the city of Vancouver,
BC, Canada.
- The SoG is a semi-enclosed ocean basin between Vancouver Island and the
mainland of British Columbia, Canada, constituting one of Canada's major ecological
marine environments.
- Movement of this plume composes part of the estuary-circulation that contributes
to the whole circulation in the SoG. It affects water properties mainly due to
the distinct stratified layer between upper brackish water and lower ocean water. It
also causes impacts on marine biology in this region.
- Developing a numerical ocean model to better predict the surface currents in the
Fraser River plume has important implications for accurately modelling circulation
within the SoG, the biological productivity, oil spill trajectories, marine pollutant
dispersal and for search and rescue.
Objectives
To improve the surface flows in the Fraser
River plume and tides in a three-dimensional
baroclinic model, by modifying the geometry
of the Fraser River and investigating the
effects of turbulence parameters.
Fig. 1 Satellite image of the plume sediments in the waters
of Fraser River as they pour into the SoG in June, 2003 (WHOI).
Ferry-based salinity data
Surface drifter data
1. The extended and deepened river channel generated more cross-strait
surface flow and improved the surface currents to a reasonable extent.
2. Tidal amplitudes in the Fraser estuary with this new river channel correspond
well with observations.
3. Reducing the vertical eddy viscosity and diffusivity is important to produce
weaker along-strait flow.
4. Remaining discrepancies may be partly due to the still too strong baroclinic
tides at the surface in the model, e.g., generation of internal tides at the shelf
break.
* Contact Info: jieliu@eos.ubc.ca
Nowcast:
- NEMO 3.4 version in its regional
configuration (Fig. 2).
- 398 by 898 by 40 grid cells.
- 150 rivers parameterized.
- 8 tidal constituents, temperature,
salinity, sea surface height forced at
west and north boundaries.
- Daily Fraser River discharge, hourly
model wind and 8 tidal constituents to
run daily nowcasts.
Sensitivity experiment:
Period: June 15-29, 2015
- NEMO 3.4.
- Smoothed longer and deeper river channel (bathymetry #6),
with values before New Westminster based on the chart,
beyond to set to 10 m.
- Initial temperature in the river channel of 14 o
C ,
salinity value after New Westminster as 0, before as 4 psu.
- Climatology Fraser runoff, hourly model winds, 8 tidal
constituents.
- Background vertical eddy viscosity and diffusivity of 1e-04 and
1e-05 m2
/s, respectively.
Hindcast simulations:
- Run 1: bathymetry #6, daily Fraser runoff.
- Run 2: bathymetry #6, daily Fraser runoff, 1e-05
background vertical eddy viscosity and diffusivity.
- Run 3: bathymetry #6, daily Fraser runoff, 1e-05
background vertical eddy viscosity and 1e-06 diffusivity.
Fig. 2 Salish Sea model domain including bathymetry,
rivers (green dots), and VENUS Central observational
site monitored by Ocean Networks Canada (ONC).
Fig .4 Comparison of background vertical eddy viscosity (left) /diffusivity (right) and
values calculated from turbulence scheme in the model at VENUS Central site.
Fig. 5 1.5m nowcast salinity compared with ferry salinity along the ferry route (left) and model
spatial distribution of salinity field over the whole domain, with ferry route and stations labeled on
(right).
Fig .6 Comparison of observed drifter tracks with modelled particle
trajectories. Both are released at the edge of Jetty and tracked for
29 hours.
Fig. 7 Particle trajectory comparison between nowcast and new results from
bathymetry #6.
Fig. 8 With the same data as Fig. 5, but with various 1.5m model results, left panel
is the salinity comparison along the ferry track. Right panel shows the sea surface
height at Point Atkinson, near Vancouver; the red star labels the time for comparison.
Fig. 10 Minimum salinity value (upper panel)and location (lower panel)of
deepened (bathymetry #6), reduce_visc (bathymetry #6 + lower viscosity),
observed, all_reduce (bathymetry #6 + lower viscosity + lower diffusivity), and
nowcast (bathymetry #2 + higher viscosity +higher diffusivity) along the ferry
track during the hindcast period (Oct8-10, 2014).
Table.1 Tidal amplitudes comparisons inside the Fraser River estuary.
* For Production: PO14b-2768
For Deep Water Renewal: PO24A-2914
* See PO14A-2747
Jie Liu*, Susan Allen, Nancy Soontiens
Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia,
Vancouver, BC, Canada
Data are from Ocean
Networks Canada (ONC).
- 2hrs per transect.
- 4 round trips during
weekday, fewer times
on weekends.
- Overall, the salinity
values are well
represented in the model.
- However, position of
plume is closer to the
mainland coast than data.
Data are from Dr Mark
Halverson and Dr Rich
Pawlowicz of UBC.
- Modelled surface currents
need to be improved.
- Cross-strait flow is too weak.
- Baroclinic tides are too
strong at the surface.
Data from Environment Canada, modelled results from the sensitivity experiment.
- Barotropic tide is good at the Fraser River mouth region (Steveston).
- Modelled tides are slightly higher in the Deas Island Channel and New
Westminster.
- Extremely high tidal amplitude at Mission is due to too deep and smooth
bathymetry; preliminary results show that further shallowing of the bathymetry
after New Westminster improves results.
- Canada. Department of the Environment. Institute of Ocean Sciences, P. B., Ages, A., Woollard, A.,
1976. Tides in the Fraser Estuary.
- Stronach, J. A. "The Fraser River plume, Strait of Georgia." Ocean Management 6.2 (1981):
201-221.
- Ariane tutorial and namelists: http://stockage.univ-brest.fr/~grima/Ariane/ariane_namelist_2.x.x_
oct08.pdf, http://stockage.univ-brest.fr/~grima/Ariane/ariane_tutorial_2.x.x_sep08.pdf.
EC14D-1035
Two particles are released at
the same position. The
trajectories (Fig. 7) record
the 46 hrs duration tracks.
The striking feature is the
new result with bathymetry
#6 goes further offshore when
compared with the nowcasts,
which demonstrates our
hypothesis that the extended
and deepened river channel
generates stronger cross-strait
flows.
Fig. 9 Modelled particle trajectories of lower viscosity run case, both lower
viscosity and diffusivity case, respectively.
Period: October 8-10, 2014
The data is on Fig. 6
- For the ferry-based salinity comparison, the
new results (bathymetry #6,reduced viscosity,
reduced both viscosity and diffusivity), the
location of minimim salinity value for the
modelled result along the ferry track moves
around 2/3 way towards that of observations'.
- For the drifter-particle comparison, with
lower viscosity, both lower viscosity and
diffusivity cases, the surface flow patterns
are closer to the observed drifter track.
Statistics of the minimum salinity value and its location for various model results
are derived from the ferry data-model comparisons during the hindcast. This
provides a more comprehensive and larger picture than a single set of comparisons.
- The case of lowered viscosity and diffusivity plus bathymetry #6, best matches the
observed value and location.
- Some external forcing factors, e.g., winds and tides, which will induce mixing and
advection of the surface flow, may account for the discrepancies of plume position.
Fig. 3 Salish Sea model domain with
original river channel (bathymetry #2), in
the upper panel and new river channel
(bathymetry #6) in the lower panel.
Tidal amplitude
Station names Distance
from
mouth
[km]
Observed
max
amplitude
[m]
Observed
min
amplitude
[m]
Observed
average
amplitude
[m]
Modelled
max
amplitude
[m]
Modelled
min
amplitude
[m]
Modelled
average
amplitude
[m]
Steveston
Deas Island Channel
New Westminster
Mission
1
18
36
52
3.49
3.05
2.28
0.37
2.10
1.85
1.43
0.24
2.88
2.58
1.91
0.31
3.72
3.55
3.02
3.00
2.03
2.04
1.78
1.71
2.89
2.80
2.42
2.37