1. Sensitivity of the Fraser River Plume
to Winds, Tides and Freshwater Flux
Jie Liu, Susan Allen, Nancy Soontiens
Earth, Ocean and Atmospheric Sciences
The University of British Columbia

2. Mixing in the plume • Rivers carry more than
one-third of land-based
precipitation to the ocean
(Trenberth et al., 2007).
• Impact of the river plume
on shelf circulation and
ecosystem health partly
depends on the vertical
mixing dilution rate
(A.R.Horner-Devine et al.,
2015).
• Multiple forcing factors
contribute to mixing in the
river plume.
R.D.Hetland, 2005
1

3. Objective
Examine the sensitivity of the mixing of the Fraser River
plume to external forcing factors, especially tides and winds in
a three-dimensional numerical model.
2

4. Outline
• Model description
• The Fraser River plume
• Model runs
• Analysis
• Results
• Conclusion and future work
3

5. Model description
• NEMO 3.4
• ~500m horizontal
1-27m vertical
• Improved from
Soontiens et al., 2015,
with a long river and
decreased background
vertical eddy viscosity
to sm
125-
101


4

6. The Fraser River plume
5

7. Model runs
• Run 1： only Fraser River (baseline)
• Run 2: Run1 + tides (no winds)
• Run 3: Run1 + winds (no tides)
• Run 4: Run1+ tides + winds (combine all)
• Period: September 25~October 31, 2014
• Analysis: October 27~October 31, 2014
6

8. Geometry of analysis
• Long river
channel
• River flows in the
last five days of
October, 2014:
~2500 sm
13 
7

9. • only river case:
strongest
stratification
• Winds are more
important than tides
for vertical mixing at
south of Sandheads,
indicating it is in the
far-field region.
Results
Run1: only river Run2: river + tides
Run3: river + winds Run4: river + tides+ winds
8

10. Rmix =
S
Ssur
0
f
Where is the
surface salinity and
is the averaged salinity
in the water column.
Ssurf
S0
9
(E.Masunaga et al.,
2011)

11. Run1: only river Run2: river + tides
Run3:
river +
winds
Run4: river +
tides+ winds
10

12. Summary of Rmix along the transect
11

13. Spatial distribution of Rmix
All – (river + tides) = winds All – (river + winds) = tides
12

14. Conclusion
• Near-field and far-field mixing are reproduced in the model at a moderate
river flow period. Near-field region extends about 12 km from the river
mouth of Steveston in the model.
Future work
• Investigate the mixing in the plume response to forcing factors under the low
and high river flows conditions, respectively.
• Isolate and quantify the total volume flux and fresh water transport at
along/cross-strait transect advected by each forcing agent.
13

15. Reference
Trenberth, Kevin E., et al. "Estimates of the global water budget and its
annual cycle using observational and model data." Journal of
Hydrometeorology 8.4 (2007): 758-769.
Hetland, Robert D. "Relating river plume structure to vertical
mixing." Journal of Physical Oceanography 35.9 (2005): 1667-1688.
Horner-Devine, Alexander R., Robert D. Hetland, and Daniel G.
MacDonald. "Mixing and transport in coastal river plumes." Annual Review
of Fluid Mechanics47 (2015): 569-594.
Soontiens, Nancy, et al. "Storm Surges in the Strait of Georgia Simulated
with a Regional Model." Atmosphere-Ocean (2015): 1-21.
Masunaga, Eiji, Oliver B. Fringer, and Hidekatsu Yamazaki. "An
observational and numerical study of river plume dynamics in Otsuchi Bay,
Japan." Journal of Oceanography (2015): 1-19.

16. Thank you!
Any questions?