lutocline formation by waves
Post on 03-Jan-2016
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Lutocline formation by waves
Susana B. Vinzon
Universidade Federal do Rio de Janeiro
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Lutocline generation: source of sediments?-Ressuspension from the bottom by tidal currents and/or waves-Deposition from suspension
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0,01 0,10 1,00 10,00
Concentration (g/l)
De
pth
(m
)
slackflood-ebb
Lutoclines :Steps in suspended sediment
concentration
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100
0
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10
15
concentration (g/l)
dept
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320 g/l
Secondary
Primary
Tidal currents:
Amazon Shelf data
AMASSEDS project
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Salt stratification effect:
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concentration (g/l)
sett
ling
velo
city
(m
m/s
)
10-1
100
101
102
10-4
10-3
10-2
10-1
100
101
Hindered settling effect:
Flocculation
Hindered Settling
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1 0- 2
1 0- 1
1 00
1 01
1 02
1 03
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1 0
s e d i m e n t c o n c e n t r a t i o n ( g / l )
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h (m
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s e c o n d a r yl u t o c l i n e
p r i m a r yl u t o c l i n e
1 0- 2
1 0- 1
1 00
1 01
1 02
1 03
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s e d i m e n t c o n c e n t r a t i o n ( g / l )
dept
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1 0
Ws: uniforms: uniform
Lutocline simulations
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Steady state turbulent kinetic energy balance
wg
dz
duvu
Shear production
z
u 3
2uwu
1
ew
wsvs H
zCgww
g
Buoyancy
Dissipation
Tz
kau rb
3
16.0Wave-mean turbulence intensity
(Sleath,1991)
Lutocline generation by waves
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Lutocline height:
4
1
3
2
33
65.0
w
wsvs
rbe
CgwT
kaH
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h (m
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0
0,02
0,04
0,06
0,08
0,1
0 0,02 0,04 0,06 0,08 0,1
measured lutocline height (m)
calc
ula
ted
lu
tocl
ine
he
igh
t (m
)ws = 0.05 mm/s
kr = 2 cm
Laboratory results:
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Field data (Traykovski et al 2000):
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Discussion
• Closer look at the wave turbulence model
(for field conditions)
• Limitation of the lab experiments (Re)
• The model considers no erosion threshold
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Importance of Primary Lutocline for sediment transport:
10-4
10-2
100
102
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Concentration (g/L)
Dep
th (
m)
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Time
depth
depth
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0
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VelocityD
ep
th0
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Velocity
De
pth
First Hypothesis
No mud layer
High measured velocities near bottom due to log profile
Mud layer
High measured velocities near bottom because the profiler don’t find the true bottom
Second Hypothesis
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How to know which one is correct?
Do we need new field techniques for measuring SSC and velocities below the primary lutoclines?
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