rijkswaterstaat
dienst getijdewateren
ir
- C-4704, 29
bibliotheek
715
PZ: tblBft
29. Erosion and deposition characteristics of natural muds
Sediments from theWester schelde (Breskens)
Cohesive Sedime
Rijkswaterstaat
Delft Hydraulics
rijkswaterstaat
dienst getijdewateren
bibliotheek
Report 29. Erosion and deposition characteristics of natural muds
Sediments from theWesterschelde (near Breskens)
C. Kuijper
J.M. Cornelisse
J.C. Winterwerp
November 1990
Cohesive Sediments
Rijkswaterstaat
Delft Hydraulics
1
CONTENTS
Nomenclature
L i s t of f i g u r e s
ABSTRACT
1. INTRODUCTION
1
2. FIELD SAMPLING
3
3. EXPERIMENTAL PROCEDURE AND MEASUREMENTS
3.1 The a n n u l a r flume
3.2 P r e p a r a t i o n s
3.3 T e s t s on d e p o s i t i o n
3.4 T e s t s on e r o s i o n
3.5 T i d a l e x p e r i m e n t s
4
4
5
5
6
6
4. SEDIMENT PROPERTIES
4.1 P h y s i c o - c h e m i c a l a n a l y s e s
4.2 G r a i n s i z e d i s t r i b u t i o n
4.3 S e t t l i n g v e l o c i t y
4.4 R h e o l o g i c a l p r o p e r t i e s
7
7
8
8
9
5. RESULTS ON DEPOSITION
5.1 C r i t i c a l bed shear s t r e s s f o r d e p o s i t i o n
5.2 G r a i n s i z e , pH and r e d o x - p o t e n t i a l i n t h e s u s p e n s i o n
5.3 P h y s i c o - c h e m i c a l p r o p e r t i e s o f t h e s u s p e n s i o n
11
11
12
13
6. RESULTS ON CONSOLIDATION
6.1 C o n s o l i d a t i o n c u r v e s
6.2 Pore w a t e r p r e s s u r e
6.3 Dry d e n s i t y p r o f i l e s
14
14
14
14
7. RESULTS ON EROSION
7.1 C r i t i c a l bed shear s t r e s s f o r e r o s i o n
7.2 E r o s i o n parameters
7.3 G r a i n s i z e , pH and r e d o x - p o t e n t i a l i n t h e s u s p e n s i o n
16
16
16
18
7.4 P h y s i c o - c h e m i c a l
p r o p e r t i e s of the suspension
8. TIDAL EXPERIMENTS
Acknowledgements
REFERENCES
FIGURES
APPENDIX A - DESCRIPTION OF TEST PROGRAM
APPENDIX B - CALIBRATION CURVES
18
20
Nomenclature
a, b
- n o n - d i m e n s i o n l e s s c o n s t a n t s i n e q u a t i o n (1)
c
- s u s p e n s i o n c o n c e n t r a t i o n of t h e sediment
[kg/m ]
co
c
eq
- i n i t i a l sediment c o n c e n t r a t i o n ( o f t h e s u b t e s t )
[kg/m ]
3
3
- e q u i l i b r i u m sediment c o n c e n t r a t i o n
(of
s
the s u b t e s t )
[kg/m ]
D
- p a r t i c l e diameter
[m]
h
- w a t e r depth
[«]
M
- e r o s i o n parameter i n e q u a t i o n (5)
[kg/m /s]
r
- r a d i u s o f t h e a n n u l a r flume
[m]
t
- time
[s],[min]
V.
- longitudinal velocity
[m/s]
c
- erosion rate
[kg/m /s]
e
f
- f l o c erosion rate
[kg/m /s]
z
b
- bed shear s t r e s s
[Pa]
z
- critical
shear s t r e s s f o r d e p o s i t i o n
[Pa]
- critical
shear s t r e s s f o r e r o s i o n
[Pa]
d
z
e
r _a( z )
u
'2
>
b
P
p
s
p
w
"a
t
(r./x .-1).o
b d
B 0
2
2
2
- bed s t r e n g t h p r o f i l e
[Pa]
- a n g u l a r v e l o c i t y of the annular r i n g
[rad/s]
- angular v e l o c i t y of the channel
[rad/s]
- b u l k d e n s i t y o f t h e sediment
[kg/m ]
- d e n s i t y of sediment p a r t i c l e s
[kg/m ]
3
3
3
d e n s i t y of the water
[kg/m ]
model parameter ( e q . 2)
[-]
- model parameter (eq. 2)
- model parameter ( e q . 3)
- model parameter ( e q . 3)
[min]
[-]
[-]
- model parameter ( e q . 3)
[-]
- model parameter ( e q . 6)
- model parameter ( e q . 6)
[Pa
[-]
a
(J
Note:
Most q u a n t i t i e s a r e g i v e n i n S i - u n i t s , e.g.: "mass" i n "kg",
]
"time"
in
and
"length"
i n "m".
However, because o f p r a c t i c a l r e a s o n s some
s
exceptions occur i n the t e x t :
CEC:
[meq/100
conductivity:
[mS/cm]
g]
Vi
SAR:
[(meq/1) ]
settling velocity:
[mm/s]
s p e c i f i c surface:
[m /g]
2
L i s t of f i g u r e s
figure
1
sampling l o c a t i o n
figure
2
a n n u l a r flume
figure
3
photographs of sediment and sediment p a r t i c l e s
figure
4
d i s t r i b u t i o n of s e t t l i n g
figure
5
rheological flow-curves
figure
6
dynamic v i s c o s i t y of the sediment as a f u n c t i o n
sediment
velocity
7
y i e l d s t r e s s as a f u n c t i o n of the sediment
figure
8
concentration-time
normal f i t s
9
the
concentration
figure
figure
of
curves
during
concentration
deposition
( i n i t i a l c o n c e n t r a t i o n : 0.76
and l o g s
kg/m )
e q u i l i b r i u m c o n c e n t r a t i o n as a f u n c t i o n of the bed s h e a r
stress
figure
10
p a r t i c l e s i z e d u r i n g experiment on d e p o s i t i o n
f i g u r e 11
pH d u r i n g experiment on d e p o s i t i o n
figure
redox p o t e n t i a l d u r i n g experiment on d e p o s i t i o n
12
f i g u r e 13
sediment-water i n t e r f a c e d u r i n g c o n s o l i d a t i o n
figure
pore w a t e r p r e s s u r e d u r i n g c o n s o l i d a t i o n
14
f i g u r e 15
d r y d e n s i t y p r o f i l e s i n the bed
figure
concentration-time
16
c u r v e s d u r i n g e r o s i o n of the sediment
l a y e r : c o n s o l i d a t i o n p e r i o d of 1 day
figure
17
erosion
rate
during
erosion
experiment on a sediment
l a y e r : c o n s o l i d a t i o n p e r i o d of 1 day
figure
18
particle
s i z e d u r i n g e r o s i o n on a sediment l a y e r w i t h a
c o n s o l i d a t i o n p e r i o d of 1 day
figure
19
pH d u r i n g e r o s i o n t e s t s
figure
20
redox p o t e n t i a l d u r i n g e r o s i o n t e s t s
f i g u r e 21
d e p o s i t i o n and e r o s i o n under t i d a l
figure
z, - 0.2 Pa
D
d e p o s i t i o n - r a t e and e r o s i o n - r a t e under t i d a l
figure
figure
22
23
24
conditions:
conditions:
z. - 0.2 Pa
D
sediment c o n c e n t r a t i o n as a f u n c t i o n of the bed s h e a r
s t r e s s : t . - 0.2 Pa
b
p a r t i c l e s i z e d u r i n g t i d a l e x p e r i m e n t : z^ - 0.2 Pa
f i g u r e 25
d e p o s i t i o n and e r o s i o n under t i d a l
figure
26
z. - 0.4 Pa
D
d e p o s i t i o n - r a t e and e r o s i o n - r a t e under t i d a l
conditions:
27
z^ - 0.4 Pa
D
sediment c o n c e n t r a t i o n as a f u n c t i o n of the
bed
figure
stress:
0.4
Pa
conditions:
shear:
ABSTRACT
A
sediment
sample
from
the
Western S c h e l d t
i n v e s t i g a t e d w i t h respect to i t s behaviour
annular
flume
processes.
is
used
to
quantify
(harbour
of B r e s k e n s ) i s
on d e p o s i t i o n and e r o s i o n .
the
parameters
P a r a l l e l t o these t e s t s v a r i o u s
governing
physico-chemical
An
these
properties
of the sediment are d e t e r m i n e d .
The
sediment m a i n l y c o n s i s t s of q u a r t z , f e l d s p a r and
quantities
calcite,
cohesiveness
Cation
chlorite,
dolomite
and
of the sediment i s i n d i c a t e d w i t h a v a l u e
Exchange
Capacity.
s p e c i f i c s u r f a c e o f 111.5
fraction
kaolinite,
i l l i t e and
smaller
sand f r a c t i o n (>63
than
um)
The
2
m /g
less
smectite.
of
10
The
for
the
sediment i s f u r t h e r c h a r a c t e r i s e d by a
and
an
organic
16 um amounts 54%.
of 12% and
in
Two
content
of
5%.
The
d i f f e r e n t samples show a
27% r e s p e c t i v e l y . The
fluid
is
saline
w i t h a Sodium A d s o r p t i o n R a t i o v a r y i n g d u r i n g the e x p e r i m e n t s between 35
and
38.
The
critical
s h e a r s t r e s s f o r d e p o s i t i o n i s 0.06
± 0.01
Pa. Below t h i s
v a l u e complete d e p o s i t i o n o c c u r s as f o r h i g h e r v a l u e s p a r t i a l d e p o s i t i o n
takes
place.
The
concentration-time
curves
e q u a t i o n a c c o r d i n g t o Mehta and P a r t h e n i a d e s .
and
are
The
approximated by
parameters (z^/z^-l)--
Oj are i n the range of 1.3-2.4 and 0.5-0.8 r e s p e c t i v e l y . The
s e t t l i n g v e l o c i t y of the sediment i n the f l o c c u l a t e d s t a t e i s
as
0.23
mm/s
(at
an
initial
concentration
d e f l o c c u l a t e d a median s e t t l i n g v e l o c i t y of 0.12
of
estimated
3
0.84
mm/s
median
kg/m ).
When
i s measured.
I n the a n n u l a r flume as w e l l as i n a s e p a r a t e
column a sediment bed
a c o n s o l i d a t i o n p e r i o d of 1 day
The
settling
in
is
placed.
s t i l l water w i t h a depth of 0.3
of c o n s o l i d a t i o n the d r y d e n s i t y near the
m.
the
layer
One
is
formed
day a f t e r the
surface
amounts
with
by
start
3
110
kg/m .
3
A f t e r 3 days the d r y d e n s i t y near the s u r f a c e i s i n c r e a s e d t o 140 kg/m .
The
d r y d e n s i t y p r o f i l e shows v a l u e s up t o 700 kg/m
The water o v e r p r e s s u r e
3
near
the
i s l a r g e l y d i s s i p a t e d d u r i n g the f i r s t
bottom.
day.
At the s t a r t of the e r o s i o n experiment ( c o n s o l i d a t i o n p e r i o d : 1
top
layer
for
a bed
of
0.4
of
a few mm
day)
a
i s p r e s e n t . E r o s i o n t a k e s p l a c e at a s m a l l r a t e
shear s t r e s s of 0.2
Pa and
i s enhanced f o r a bed
shear
stress
Pa. The
c r i t i c a l bed s h e a r s t r e s s i s t h e r e f o r e e s t i m a t e d as 0.2_3
0.3 Pa. E r o s i o n r a t e s are 0.6 10
kg/m /s or l e s s depending upon the
magnitude of the bed shear s t r e s s . The parameter M i n the e r o s i o n r a t e
-3
-3
2
e q u a t i o n as suggested by K a n d i a h i s i n the o r d e r of 0.05
2
kg/m /s.
When
10
- 0.2
10
the e r o s i o n r a t e s are approximated w i t h the e r o s i o n r a t e
expression according
to
Parchure
and
Mehta
(6
-
0.5)
an
erosion
parameter or w i t h a v a l u e o f 10.4 i s found.
In a d d i t i o n t o t h e d e p o s i t i o n
under
tidal
and
erosion
two
modeltests
c o n d i t i o n s a r e performed. D u r i n g t h e t i d a l e x p e r i m e n t s t h e
maximum bed shear s t r e s s i s 0.2 Pa and 0.4
tests
experiment
the c o n s o l i d a t i o n
Pa
respectively.
For
both
p e r i o d o f t h e sediment l a y e r amounts 6 hours.
The maximum sediment c o n c e n t r a t i o n d u r i n g t h e f i r s t t i d a l experiment
is
s
l e s s t h a n 0.35 kg/m . E r o s i o n and d e p o s i t i o n i s i n i t i a t e d a t a bed shear
s t r e s s o f 0.1 Pa. The type
erosion.
The
second
of
tidal
erosion
experiment
can
be
described
displays
a
b e h a v i o u r . Due t o t h e h i g h maximum bed shear s t r e s s a
sediment
as
surface
different
erosion
large
amount
of
i s eroded r e s u l t i n g i n a maximum sediment c o n c e n t r a t i o n o f 10
s
kg/m . D u r i n g t h e d e c e l e r a t i n g phase no o r l i t t l e d e p o s i t i o n t a k e s p l a c e
when
t h e bed
shear
stress
i s i n t h e range o f 0.1 - 0.4 Pa. A r a p i d
d e c r e a s e o f t h e sediment c o n c e n t r a t i o n r e s u l t s when t h e bed s h e a r s t r e s s
drops
below 0.1 Pa. Around s l a c k water a f l u i d mud l a y e r i s formed
a t h i c k n e s s o f 60 mm. When t h e bed shear s t r e s s i s i n c r e a s e d ,
waves
at
the
interface
of
the f l u i d
mud
layer
with
internal
and t h e w a t e r a r e
o r i g i n a t e d . The b r e a k i n g o f these waves r e s u l t s i n e r o s i o n r a t e s i n t h e
order
of
1.5 10
2
kg/m /s (bed shear s t r e s s e s between 0.1 and 0.2 P a ) .
T h i s i s f o l l o w e d by a p e r i o d w i t h s u r f a c e e r o s i o n and much l o w e r e r o s i o n
rates.
- 1 -
1. INTRODUCTION
In
o r d e r t o improve t h e u n d e r s t a n d i n g
of the p h y s i c a l processes
t o t h e t r a n s p o r t o f c o h e s i v e sediments,
been
started
by
related
a l o n g - t e r m r e s e a r c h program has
t h e R i j k s w a t e r s t a a t ( M i n i s t r y o f T r a n s p o r t and P u b l i c
Works o f The N e t h e r l a n d s ) . The program i n c l u d e s p h y s i c a l e x p e r i m e n t s
at
Delft Hydraulics.
In
1989 a s t a n d a r d approach was d e f i n e d t o determine
the d e p o s i t i o n a l
e r o s i v e p r o p e r t i e s o f n a t u r a l muds i n The N e t h e r l a n d s
and
(appendix A ) .
The o b j e c t i v e s a r e :
- to
derive
t h e p r o p e r t i e s f o r muds o f s p e c i f i c s i t e s
(lakes,
r i v e r s , estuaries, coastal waters),
- to
compare
t h e outcomes
o f t h e experiments
on t h e v a r i o u s
muds and g e t i n s i g h t i n t h e ranges o f t h e parameters,
- to
e s t a b l i s h a d a t a base f o r f u r t h e r a n a l y s i s on e r o s i o n and
d e p o s i t i o n and t h e i r r e l a t i o n s w i t h b u l k
The
ultimate
parameters.
i s t o a r r i v e a t r e l i a b l e p h y s i c a l and m a t h e m a t i c a l
goal
d e s c r i p t i o n s o f t h e t r a n s p o r t p r o c e s s e s on e r o s i o n and d e p o s i t i o n and t o
i n c o r p o r a t e t h e r e s u l t s i n n u m e r i c a l models.
The
r e s e a r c h as d e s c r i b e d i n t h i s r e p o r t m a i n l y c o n s i s t s o f
in
an
experiments
a n n u l a r flume. A d d i t i o n a l measurements w i t h a r o t o - v i s c o m e t e r , a
s e d i m e n t a t i o n b a l a n c e and a c o n s o l i d a t i o n column a r e used
various
properties
chemical
of
quantities
mineralogical
t h e sediment. Furthermore,
of
t h e sediment
composition,
redox-potential,
and
to
determine
a number o f p h y s i c o -
the f l u i d
a r e measured:
C a t i o n Exchange C a p a c i t y , c o n d u c t i v i t y , pH,
chlorinity,
oxygen
and
organic
content,
Sodium
r e l a t e t o a sediment o b t a i n e d from t h e Western
Scheldt
A d s o r p t i o n R a t i o and s p e c i f i c a r e a .
The
experiments
(taken
from
t h e harbour
o f B r e s k e n s ) ( f i g u r e 1 ) . The s a m p l i n g
i n the
f i e l d and t h e m e t e o r o l o g i c a l as w e l l as
the h y d r a u l i c
described
3 a d e s c r i p t i o n i s given of the
i n chapter
2.
In
chapter
c o n d i t i o n s are
a n n u l a r flume. A t t e n t i o n i s p a i d t o t h e e x p e r i m e n t a l procedure
as
t h e measurements
parameters
Geotechnics.
i n t h e flume.
characterising
Some
t h e sediment
of
are
the
as
physico-chemical
determined
by
Delft
The r e s u l t s o f these a n a l y s e s a r e g i v e n i n c h a p t e r 4. A l s o
the measurements a t
Delft
Hydraulics
with
the roto-viscometer,
s e d i m e n t a t i o n b a l a n c e and t h e c o n s o l i d a t i o n column a r e p r e s e n t e d
chapter. Subsequently,
tests
well
i n c h a p t e r 5, 6 and 7 t h e r e s u l t s
of
the
i n this
t h e model
on d e p o s i t i o n , c o n s o l i d a t i o n and e r o s i o n i n t h e a n n u l a r flume a r e
- 2 -
d i s c u s s e d . F i n a l l y the e x p e r i m e n t a l r e s u l t s
t i d a l c o n d i t i o n s are d e s c r i b e d i n c h a p t e r 8.
of
two
experiments
under
- 3 -
2. FIELD SAMPLING
The
sediment
sample was c o l l e c t e d on October 4 1989 a t 13:00 h r s (MET)
w i t h t h e R i j k s w a t e r s t a a t m o t o r v e s s e l " D e l t a " . The s a m p l i n g was
the
done
in
harbour o f Breskens as i n d i c a t e d i n f i g u r e 1 ( x : 27289, y: 380881).
The weather c o n d i t i o n s on t h a t day can
be
described
as:
sunny,
wind
d i r e c t i o n 30°, wind v e l o c i t y 5 m/s ( B f t . 2) and a temperature o f 19 °C.
During the sampling v e r t i c a l p r o f i l e s of the c o n d u c t i v i t y ,
pH
and
temperature,
oxygen c o n t e n t were measured. The r e s u l t s a r e shown i n t a b l e 1.
Because no s t r a t i f i c a t i o n was p r e s e n t o n l y t h e depth-averaged v a l u e s a r e
presented.
The l o c a l water depth d u r i n g t h e measurements was 6.4 m. A l l
parameters i n t a b l e 1 a r e measured
with
instruments
from
Rijkswater-
staat .
conductivity
chlorinity
temperature
oxygen c o n t e n t
oxygen c o n t e n t
redox-potent i a l
- fluid
- sediment
pH ( f l u i d )
[mS/cm]
[kg/m»]
[•ci
[kg/ra ]
[X by w e i g h t ]
[mV]:
s
39.04
17.13
16.6
,
6.8 10
81.9
J
[-]
8.09
table 1 - Conditions during sampling
The sediment was c o l l e c t e d w i t h a s m a l l "van Veen" grab and was
from
t h e upper 0.15 m o f the sediment l a y e r . The water was pumped from
middepth. The sediment and t h e f l u i d were t r a n s p o r t e d t o t h e
at
laboratory
a t e m p e r a t u r e o f 4° C w i t h a r e f r i g e r a t o r c a r . A t t h e l a b o r a t o r y t h e
sediment was s t o r e d i n r e f r i g e r a t o r s a t a
4
sampled
°C
and
temperature
varying
between
8 °C. The water was kept i n a c l i m a t e c o n t r o l l e d room w i t h a
c o n s t a n t t e m p e r a t u r e o f 20 °C. B e f o r e u s i n g t h e mud f o r t h e
sediment was s i e v e d on a s c r e e n w i t h a 1 mm
lattice.
tests,
the
- 4 -
3. EXPERIMENTAL PROCEDURE AND MEASUREMENTS
3.1 The a n n u l a r flume
The a n n u l a r flume ( o r
channel
carousel)
(figure
2)
consists
of
a
circular
w i t h a mean d i a m e t e r of 2.1 m and a c h a n n e l w i d t h of 0.2 m.
The
w a t e r d e p t h i s 0.3 m. A c i r c u l a r l i d a t the s u r f a c e d r i v e s the water. I n
order
to
m i n i m i z e the e f f e c t o f secondary c u r r e n t s near the bottom the
channel i t s e l f
speeds
of
i s r o t a t e d i n the
the
opposite
direction.
velocities
above
the
bottom
that
were
found
to
of
the
measured
e l e c t r o m a g n e t i c c u r r e n t meter [ 1 ] . The p r o p o r t i o n of
is
operational
l i d and the c h a n n e l are e x p e r i m e n t a l l y d e t e r m i n e d u s i n g
s m a l l spheres w i t h a d e n s i t y s l i g h t l y l a r g e r t h a n
Furthermore,
The
water.
with
rotational
an
speeds
v a r y between 2.8 and 2.9, w h i c h i s almost the same as the
v a l u e of 3.1 d e r i v e d by Mehta and P a r t h e n i a d e s [2] i n a somewhat s m a l l e r
flume.
For
the
e x p e r i m e n t s d e s c r i b e d i n t h i s r e p o r t a v a l u e of 2.8 i s
used. The o p t i m a l r a t i o of the a n g u l a r v e l o c i t i e s of the upper
the
l i d and
c h a n n e l i s a l s o a f u n c t i o n of the water d e p t h ( [ 1 ] and [ 2 ] ) . I n the
case of e r o s i o n e x p e r i m e n t s when a sediment l a y e r i s p r e s e n t
depth
in
the
annular
flume
is
less
The
bed
shear
stresses
in
the
water
t h a n 0.30 m and changes d u r i n g
e r o s i o n . The o p e r a t i o n a l speeds of the upper l i d and
s l i g h t l y c o r r e c t e d t o account f o r t h i s
the
the
channel
are
effect.
a n n u l a r flume a r e c a l c u l a t e d w i t h an
e x p r e s s i o n as d e r i v e d by Mehta and P a r t h e n i a d e s [ 2 ] :
with,
r
V
1
b
- bed s h e a r s t r e s s [ P a ] ,
- \b>. - « |
2
r [m/s],
u. - a n g u l a r v e l o c i t y of the a n n u l a r r i n g
[rad/s],
«2 - a n g u l a r v e l o c i t y of the channel [ r a d / s ] ,
The
r
- r a d i u s of the a n n u l a r flume [m],
a
- 0.275,
b
-
sediment
1.37.
suspension
is
pumped from the flume a t middepth (0.14 m
above the c h a n n e l bottom) and l e d t h r o u g h a s m a l l c e l l w i t h
of
5
mm
in
probe.
diameter
w h i c h the l i g h t a d s o r p t i o n i s measured. The s u s p e n s i o n i s
r e t u r n e d t o the flume a t
intervals
a
samples
are
an
taken
elevation
from
of
0.24
m.
At
regular
time
the flume t o c a l i b r a t e the o p t i c a l
- 5 -
The
sampling as w e l l as t h e r o t a t i o n a l speeds o f t h e l i d and t h e c h a n n e l
are c o n t r o l l e d by a p e r s o n a l computer. A sampling f r e q u e n c y o f
is
chosen
f o r t h e experiments
between
Hz
on d e p o s i t i o n and e r o s i o n . D u r i n g t h e
t i d a l e x p e r i m e n t s t h e o p t i c a l s e n s o r i s sampled each
transmitted
1/30
minute.
t h e r o t a t i n g flume and t h e p e r s o n a l
Data
are
computer w i t h
the a i d o f an i n f r a - r e d t r a n s m i t t e r and r e c e i v e r .
The
flume
annular
i s located
inside
temperature o f 20 °C and a h u m i d i t y
of
a
80X
climate
c o n t r o l l e d room. A
guarantee
almost
constant
test conditions.
3.2
Preparations
After
t h e sediment i s s i e v e d on a 1 mm mesh ( a s m a l l amount o f w a t e r i s
added), f i v e samples a r e t a k e n t o
sediment.
The
determine
the dry density
d r y d e n s i t y i s d e f i n e d as t h e r a t i o o f t h e "dry w e i g h t "
and t h e "wet volume" and i s determined by w e i g h t i n g
before
and
t h e sediment
The
s
(not c o r r e c t e d f o r t h e o r g a n i c
d e n s i t y o f t h e f l u i d a t a c h l o r i n i t y o f 17.1 kg/m
3
temperature o f 20 °C i s 1021.5 kg/m . From t h i s a d r y d e n s i t y o f
7
kg/m
3
sample
a f t e r d r y i n g a t a temperature o f 105 °C. I t i s assumed t h a t
the d e n s i t y o f t h e sediment i s 2600 kg/m
content).
of the
3
and a
567
±
i s found. The v a l u e i s used f u r t h e r on t o c a l c u l a t e t h e amount
of sediment t o be added t o the a n n u l a r
Furthermore,
a
bulk
density
of
flume
1364
measurements ( t h e b u l k d e n s i t y i s d e f i n e d
f o r the v a r i o u s
kg/m
as
3
i s derived
the r a t i o
of
tests.
from
the
t h e "wet
w e i g h t " and t h e "wet volume").
3.3 T e s t s on d e p o s i t i o n
One
test
w i t h an i n i t i a l c o n c e n t r a t i o n o f 0.76 kg/m
t e s t c o n s i s t s of a mixing
successive
subtests
s t e p s . Each s u b t e s t
achieved.
0.5
i s performed. The
day
followed
i n w h i c h t h e bed shear s t r e s s i s lowered i n s m a l l
i s continued
until
an e q u i l i b r i u m
concentration
f o r t h e c a l i b r a t i o n o f t h e o p t i c a l instrument
t h e redox p o t e n t i a l and t h e o r g a n i c content
the m i x i n g
and
is
one day o r l e s s .
a r e a l s o used t o
determine t h e v a r i a t i o n s i n t h e g r a i n s i z e d i s t r i b u t i o n as w e l l
pH,
by
W i t h t h e sediment used i n t h e study t h i s s i t u a t i o n i s reached
a f t e r approximately
Samples
period of approximately
3
period preceding
analysed
at
Delft
during the t e s t .
as t h e
During
the experiment a sample o f 1000 ml i s t a k e n
Geotechnics
w i t h r e s p e c t t o c o n d u c t i v i t y , pH,
r e d o x - p o t e n t i a l , c h l o r i n i t y , oxygen and o r g a n i c c o n t e n t
and c a t i o n s .
- 6 -
3.4 T e s t s on e r o s i o n
One
erosion
test
i s carried
out i n o r d e r t o determine t h e e r o s i o n a l
c h a r a c t e r i s t i c s o f t h e sediment.
sediment
layer
with
a
The
consolidation
experiment
period
i s performed
on
a
o f one day w i t h a l a y e r
t h i c k n e s s o f 0.055 m. The sediment bed i s formed by d e p o s i t i o n i n
still
water a f t e r a m i x i n g p e r i o d o f a p p r o x i m a t e l y 12 h o u r s . The c o n c e n t r a t i o n
of
3
t h e i n i t i a l s u s p e n s i o n i s 55 kg/m .
The
erosional
behaviour
i n c r e a s i n g t h e bed shear
of
each
stress
sediment
layer
i n successive
i s determined
steps
of
1-2
by
hours.
Samples a r e w i t h d r a w n from t h e flume f o r a n a l y s e s on t h e g r a i n s i z e , t h e
sediment c o n c e n t r a t i o n ( f o r t h e c a l i b r a t i o n o f t h e o p t i c a l
probe),
pH,
r e d o x - p o t e n t i a l , oxygen and o r g a n i c c o n t e n t , c h l o r i n i t y and c a t i o n s .
The d r y d e n s i t y p r o f i l e w i t h i n t h e bed i s deduced from measurements i n a
s e p a r a t e column. A t t h e end o f t h e m i x i n g p e r i o d t h e column i s f i l l e d t o
a h e i g h t o f 0.3 m w i t h a sediment s u s p e n s i o n
from
the annular
flume.
A p a r t from t h e h e i g h t o f the sediment-water i n t e r f a c e t h e w a t e r p r e s s u r e
at
t h e bottom
of
the c y l i n d e r
i s measured.
The
results
of the
measurements i n t h e c o n s o l i d a t i o n column a r e d e s c r i b e d i n c h a p t e r 6.
3.5 T i d a l e x p e r i m e n t s
Two
experiments
under t i d a l c o n d i t i o n s a r e performed. The t i d a l
period
i s t a k e n as 12 h o u r s . The a n g u l a r v e l o c i t y o f upper l i d and c h a n n e l v a r y
according
to
a
s i n e f u n c t i o n . D u r i n g t h e f i r s t experiment t h e maximum
bed shear s t r e s s i s 0.2 Pa. F o r t h e second experiment
t h e maximum
shear
bed
stress
i s taken
as
0.4
d e p o s i t i o n i n s t i l l water a f t e r a
hours.
The
0.07 m.
The
mixing
sediment
period
of
i s formed by
approximately
i n i t i a l c o n c e n t r a t i o n o f t h e s u s p e n s i o n i s 54 kg/m
f i r s t e x p e r i m e n t and
consolidation
Pa.
period
50
of
kg/m
6
3
f o r the
second
bed
experiment.
3
12
f o r the
After
a
hours t h e t h i c k n e s s o f t h e sediment bed i s
- 7 -
4. SEDIMENT PROPERTIES
4.1 P h y s i c o - c h e m i c a l a n a l y s e s
The p h y s i c o - c h e m i c a l p r o p e r t i e s and t h e m i n e r a l o g i c a l c o m p o s i t i o n o f t h e
sediment,
as
determined
by D e l f t G e o t e c h n i c s , a r e p r e s e n t e d i n t a b l e 2
and t a b l e 3. The samples o f t h e (wet) sediment a r e t a k e n
after
sieving
(see c h a p t e r 2 ) .
conductivity
chlorinity
oxygen c o n t e n t
oxygen c o n t e n t
redox-potential
PH
organic content
Na
K
Mg
Ca
Fe
C. E • C.
dry content )
s p e c i f i c area
1
[raS/cra]
[mg/kg]
[kg/m ]
[X]
[mV]
[-]
[X by we i g h t ]
[meq/100 gds]
> i
s
• >
[g/kg]
[X]
[m /g]
a
7. 8
6500 , -3
2.5 10
30
-310
7. 63
5. 3
2. 8
1. 3
8. 4
14
18
10
41
111 5
table 2 - Physico-chemical properties of the
sediment
) dry weight/total weight
100 gds - 100 grams dry sediment
1
The m i n e r a l o g i c a l c o m p o s i t i o n o f t h e sediment i s examined by means o f Xray
d i f f r a c t i o n . Some p r o p e r t i e s o f t h e c l a y m i n e r a l s
as
density,
CEC
and s p e c i f i c a r e a a r e a l s o mentioned i n t a b l e 3.
X by
weight
- 3
7
20
< 3
33
20
12
3
smectite
chlorite
illite
kaolinite
montmorillonite
quartz
feldspar
calcite
dolomite
1
p sed.
[kg/m ]
CEC
1
1
a
s
2600-2900
2600-2860
2610-2640
2350-2700
2650
sp.area
[m /g]
40
3-8
80
80
13 - 26
768 -847
2720
2850
table 3 - Mineralogical composition and properties
additional data from: Lambe [9], Taylor [10]
and Committee on Tidal Hydraulics [11J.
1
In
figure
3
some
camera connected
pictures
o f t h e sediment a r e shown made w i t h a CCD
t o a microscope.
- 8 -
4.2 G r a i n s i z e
A
Malvern
distribution
p a r t i c l e s i z e r i s used t o f i n d t h e p a r t i c l e s i z e
of t h e sediment. The i n s t r u m e n t
of
a
laser
beam
around
i s based on t h e p r i n c i p l e o f d i f f r a c t i o n
particles
(according
d i s t r i b u t i o n s down t o a ( e q u i v a l e n t ) diameter
although
i t i s suspected
distribution
to
Fraunhofer).
Size
o f 1.2 pm can be measured,
t h a t measurements o f p a r t i c l e s s m a l l e r than
f i v e m i c r o n s a r e u n r e l i a b l e . W i t h a s m a l l s t i r r e r t h e sediment
is
kept
i n s u s p e n s i o n d u r i n g t h e measurements. The samples a r e n o t d e f l o c c u l a t e d
by means o f an u l t r a s o n i c treatment
The
10X,
or application
501 and 90X p a r t i c l e d i a m e t e r s
of
a deflocculant.
as w e l l as t h e Stokes
3
settling
3
v e l o c i t y a r e g i v e n i n t a b l e 4 (p - 2600 kg/m , p - 1022 kg/m , v -6
s
w
10~
m / s ) . The p r e s e n t e d
values are obtained a f t e r averaging over 5
l
d i f f e r e n t samples ( i n i t i a l samples
erosion
and
t i d a l experiments).
at
the
start
of
the d e p o s i t i o n ,
A l l measurements a r e done w i t h t h e 100
mm l e n s , s u i t e d f o r p a r t i c l e s up t o 188 pm. Some
samples
a r e measured
t w i c e , i . e . w i t h a d i f f e r e n t sample c o n c e n t r a t i o n ( ' o b s c u r a t i o n ' ) . I t i s
remarked here t h a t some measurements w i t h t h e 300 mm l e n s (up t o 564 pm)
result
i n much
larger
values f o r the d
a n
B 0
reasons o f c o n s i s t e n c y w i t h t h e p r e c e d i n g
natural
muds
only
the
results
d d,
0
p a r t i c l e s i z e s . For
experimental
obtained
with
the
programs
100
with
mm l e n s a r e
presented.
x<
particle
diameter
10
50
90
4 pm
11 pm
53 pm
settling
velocity
0.01 mm/s
0.10 mm/s
2.36 mm/s
table 4 - Malvern measurements
4.3 S e t t l i n g
The
grain
velocity
size
and
t h e s e t t l i n g v e l o c i t y can be r e l a t e d a c c o r d i n g t o
S t o k e s ' law assuming s p h e r i c a l p a r t i c l e s . I n a s e t t l i n g
the
fall
velocity
column
i s measured more d i r e c t l y . A s e d i m e n t a t i o n
( t y p e : S a r t o r i u s ) i s used w i t h a f a l l h e i g h t o f 0.2 m and
550
ml.
At
the
start
of
the
a
however
balance
volume
of
t e s t t h e wet sediment i s added t o t h e
s e t t l i n g column and t h e s u s p e n s i o n w i t h a c o n c e n t r a t i o n o f a p p r o x i m a t e l y
1
kg/m
3
i s mixed
uniformly
over
the
h e i g h t o f t h e column. T h i s i s
a c h i e v e d w i t h a number o f v e r t i c a l s t r o k e s w i t h t h e b a l a n c e . The
is
followed
by
a
deposition
c u m u l a t i v e mass on t h e balance
period
mixing
o f t h r e e hours d u r i n g w h i c h t h e
i s r e c o r d e d . Data a r e sampled a t
a
rate
- 9 -
o f 1 Hz and p r o c e s s e d on a p e r s o n a l computer. The temperature d u r i n g t h e
test
i s kept
constant
at
20
°C.
The
t o t a l mass on t h e b a l a n c e i s
determined
1 day a f t e r t h e s t a r t o f t h e e x p e r i m e n t , when i t
that
sediment
the
i s c o m p l e t e l y s e t t l e d . From t h i s v a l u e t h e i n i t i a l
c o n c e n t r a t i o n i s e s t i m a t e d as 0.84 kg/m
3
2600
kg/ra ).
The
i s assumed
resulting
3
(assuming a sediment d e n s i t y o f
settling
distribution
f i g u r e 4. From t h i s curve a median s e t t l i n g v e l o c i t y
curve i s g i v e n i n
of
0.23
mm/s
d e r i v e d ( e q u i v a l e n t p a r t i c l e d i a m e t e r : 16 pm). A d d i t i o n o f Na,P0
f l o c c u l a t i o n (!), p o s s i b l y
c a l c i u m and phosphate
due
to
a
chemical
reaction
4
is
causes
between
the
i o n s . T h e r e f o r e these r e s u l t s a r e n o t p r e s e n t e d i n
f i g u r e 4.
At D e l f t G e o t e c h n i c s a S e d i g r a p h P a r t i c l e S i z e r i s used t o d e t e r m i n e t h e
p a r t i c l e s i z e d i s t r i b u t i o n . The s e t t l i n g v e l o c i t y i s measured and
Stokes'
law
3
kg/m , p
an
equivalent
p a r t i c l e d i a m e t e r i s c a l c u l a t e d (p
3
- 2600
2
- 1022 kg/m , v - 10
w
using
m /s). A d e f l o c c u l a n t ( N a P 0 . 6 H 0 ) i s
4
2
7
a
added t o d i s p e r s e t h e sediment. The r e s u l t s o f two d i f f e r e n t samples a r e
shown i n t a b l e 5.
settling
velocity
[mm/s]
eq. p a r t .
diameter
2
4
6
8
10
28
38
42
45
48
0.003
0.01
0.03
0.05
0.08
pm
pm
pm
pm
pm
eq. p a r t .
diameter
%<
X<
by
by
wgt. wgt.
24
35
42
46
49
16
30
38
53
63
settling
velocity
[mm/s]
54
67
72
85
88
0.22
0.76
1.22
2.36
3.34
pm
pm
pm
pm >)
pm )
1
X<
X<
by
by
wgt. wgt.
55
65
68
70
73
table 5 - Sedigraph measurements (2 samples)
) obtained by sieving
l
4.4 R h e o l o g i c a l p r o p e r t i e s
The
rheological
properties
govern
t h e d e f o r m a t i o n o f a f l u i d u m when
s u b j e c t e d t o a f o r c e . From a f l o w c u r v e , i . e .
function
of
the
shear
stress
as
a
t h e shear r a t e , t h e y i e l d s t r e s s and t h e dynamic v i s c o s i t y
can be d e r i v e d .
Two
Haake r o t o - v i s c o m e t e r s (CV100 and RV100) w i t h two d i f f e r e n t s e n s o r s
(DA45 and MVII) a r e used f o r t h e
stress
and
the
viscosity
rheological
a r e determined
c o n c e n t r a t i o n s v a r y i n g between 50 kg/m
obtained
3
experiments.
150
and t h e " n a t u r a l "
s *
yield
f o r suspensions
i s achieved.
with
concentration
a f t e r s i e v i n g ( s e e 3.2). At the end o f a 1 minute
p e r i o d a maximum shear r a t e o f
The
acceleration
This
phase
is
f o l l o w e d by a d e c e l e r a t i o n p e r i o d w i t h the same l e n g t h . D u r i n g t h e t e s t s
- 10 -
a constant
temperature of 20 °C i s m a i n t a i n e d .
a p e r s o n a l computer w i t h a frequency
In the p r e s e n t
a decreasing
the
150
curve
viscometers
i s done w i t h
of 4 Hz.
with
shear r a t e . The v i s c o s i t y i s taken from the l i n e a r p a r t
). The
with
sampling
study the p r o p e r t i e s are d e r i v e d from the f l o w curve
'decelerating'
s
The
flow
curve
(mostly
shear
rates
between
y i e l d s t r e s s i s d e t e r m i n e d as the i n t e r c e p t
the v e r t i c a l axes. The
of
of
30
the
and
flow
f l o w c u r v e s of the sediment f o r b o t h
and v a r i o u s c o n c e n t r a t i o n s are g i v e n i n f i g u r e 5. I n
figure
6 the dynamic v i s c o s i t y as a f u n c t i o n of the c o n c e n t r a t i o n i s shown on a
l o g - l i n e a r s c a l e . The
r e s u l t i n d i c a t e s an
exponential
relationship
as
can a l s o be found i n l i t e r a t u r e [ 3 ] .
A
similar
graph,
concentration,
relating
i s presented
the
yield
stress
with
reported
sediment
i n f i g u r e 7. In t h i s case a power law seems
t o h o l d f o r the h i g h e r c o n c e n t r a t i o n s , w h i c h i s a l s o i n
measurements
the
agreement
with
i n l i t e r a t u r e [ 4 ] . I t w i l l be a p o i n t of f u r t h e r
r e s e a r c h whether the r h e o l o g i c a l p r o p e r t i e s can be r e l a t e d t o parameters
d e s c r i b i n g the d e p o s i t i o n and e r o s i o n of a c o h e s i v e
sediment.
- 11 -
5. RESULTS ON DEPOSITION
5.1 C r i t i c a l bed shear s t r e s s f o r d e p o s i t i o n
The
critical
below
bed shear s t r e s s f o r d e p o s i t i o n i s d e f i n e d
which
complete
as
the
d e p o s i t i o n o c c u r s . F o r bed shear s t r e s s e s h i g h e r
than t h e c r i t i c a l v a l u e partial deposition t a k e s p l a c e . I n t h i s
no
value
chapter
a t t e n t i o n w i l l be p a i d t o t h e well-known e q u a t i o n a c c o r d i n g t o Krone
[12].
bed
T h i s e q u a t i o n p r e d i c t s a c o n s t a n t sediment c o n c e n t r a t i o n when
shear
stress
equilibrium
curves
i s higher
concentration
with
than
the
c r i t i c a l v a l u e . The r e s u l t i n g
i s estimated
t h e use o f a log-normal
the
from
the
concentration-time
f i t . Examples o f t h i s
relationship
are g i v e n by C o r n e l i s s e e t a l [ 5 ] and K u i j p e r e t a l [ 6 ] .
§rH-
T
- T T S T -J
««•<-/»
2
*•
< <"
eq
with,
and,
T - —
°2
(2°)
t
- sediment c o n c e n t r a t i o n [kg/m ]
3
c
0
- i n i t i a l c o n c e n t r a t i o n ( o f t h e s u b t e s t ) [kg/m ]
3
c
eq
t
- e q u i l i b r i u m c o n c e n t r a t i o n ( o f t h e s u b t e s t ) [kg/m ]
- time [ s ]
a
2
The
log(-M
*0
3
c
t
1 0
B 0
- model parameter [-]
~ model parameter [ s ]
measurements
as
w e l l as t h e log-normal
f i t s are given i n f i g u r e 8
3
( i n i t i a l c o n c e n t r a t i o n : 0.76 kg/m ).
initial
cone.: 0.76 kg/m
c
t
eq
[Pa] [kg/m ] [kg/m ] [min]
0.4
0.3
0.2
0.15
0.125
0.1
0.075
0.05
0.1
0.075
3
B 0
3
3
0.745
0.654
0.516
0.360
0.344
0.306
0.224
0.057
0.785
0.730
0.640
0.518
0.335
0.341
0.309
0.222
0.050
-0.002
0.177
0.011
5
8
75
246
68
106
152
459
20
38
[-]
0.218
1.262
0.753
0.759
1. 252
0.636
0.597
0.547
1.094
0.896
table 6 - Model parameters for
concentration - time functions
(resuspended)
(resuspended)
- 12 -
Values
for t
s
o
and o
f o r each s u b t e s t a r e g i v e n i n t a b l e 6, t o g e t h e r
2
w i t h t h e i n i t i a l and e q u i l i b r i u m c o n c e n t r a t i o n .
The
c a l c u l a t e d e q u i l i b r i u m concentration i s normalized w i t h the i n i t i a l
v a l u e and i s g i v e n i n f i g u r e 9 as a f u n c t i o n o f t h e
From
bed
shear
stress.
f i g u r e 9 t h e c r i t i c a l bed shear s t r e s s i s e s t i m a t e d as 0.06 ± 0.01
Pa. A f u n c t i o n a l r e l a t i o n s h i p can
equilibrium
be
derived
between
the
normalized
( c /c_) and t h e bed s h e a r s t r e s s parameter
eq U
(z./z. - 1 ) , see e.g. Mehta and P a r t h e n i a d e s [2] and [ 6 ] .
b a
cf
concentration
" 7(210 - '
"iog[(y*
with,
Y
d
- P < - /2) dw
- n / ( y *
d
-
(3a)
p.q]
Y
(3b)
<*1
and,
z^ - bed shear s t r e s s [Pa]
z. - c r i t i c a l bed shear s t r e s s f o r d e p o s i t i o n [Pa]
a
(z,/z, - 1)« ~ model parameter [-]
b a
o, - model parameter [-]
0
E s t i m a t e s o f t h e parameters
critical
are given i n t a b l e 7 f o r three values of the
shear s t r e s s .
number.of
datapoints
°1
9
2.41
0.57
- 0.05 Pa
d
9
1.78
0.65
t . - 0. 06 Pa
a - 0. 07 Pa
9
0.78
1.32
d
table 7 - Deposition parameters for equilibrium concentration
z
5.2 G r a i n s i z e . pH and r e d o x - p o t e n t i a l i n t h e s u s p e n s i o n
D u r i n g t h e d e p o s i t i o n experiment
with
decreasing
bed
shear
the g r a i n s i z e ( D
stress,
indicating
B 0
and D,„)
a
decreases
loss of the l a r g e r
p a r t i c l e s from t h e s u s p e n s i o n ( f i g u r e 10). T h i s e s p e c i a l l y h o l d s f o r D
J0
w h i c h becomes a p p r o x i m a t e l y h a l f o f t h e i n i t i a l v a l u e .
The pH measurents a r e p r e s e n t e d i n f i g u r e 11 showing a s l o w l y d e c r e a s i n g
value
from
7.8
to
7.65. T h i s i s somewhat lower than t h e v a l u e o f 7.9
as a n a l y s e d by D e l f t G e o t e c h n i c s
( a t the s t a r t o f t h e t e s t ) .
l e s s t h a n t h e v a l u e measured d u r i n g t h e f i e l d
sampling
I t i s also
( 8 . 1 ) . The redox-
p o t e n t i a l p r e s e n t e d i n f i g u r e 12 v a r i e s between 150 mV and 240 mV
is
completely
different
(-60 mV, see t a b l e 8 ) .
from
t h e v a l u e o b t a i n e d by D e l f t
which
Geotechnics
- 13 -
5.3 P h y s i c o - c h e m i c a l p r o p e r t i e s o f t h e s u s p e n s i o n
A
sample,
taken
experiment,
content,
during
the mixing
period
preceding the d e p o s i t i o n
i s a n a l y s e d w i t h r e s p e c t t o c o n d u c t i v i t y , oxygen and o r g a n i c
chlorinity,
pH,
r e d o x - p o t e n t i a l and c a t i o n s . The r e s u l t s a r e
shown i n t a b l e 8.
Property of suspension
conductivity
chlorinity
oxygen c o n t e n t
oxygen c o n t e n t
redox-potential
pH
organic content
Na
K
Mg
Ca
Sod. Ads. R a t i o
[mS/cm]
[kg/m ]
[kg/«"]
[X by w e i g h t ]
[mV]
[-]
[X by w e i g h t ]
[kg/m ]
C
0
-0.76 kg/m
3
34.3
1
3
> >
[(meq/1)*]
1 8
-3
3.4 10
40
-60
7.90
9.8
5.600
0.340
0.950
0.130
37.56
table 8 - Physico-chemical properties of the suspension
during the deposition experiment (Delft Geotechnics)
- 14 -
6. RESULTS ON CONSOLIDATION
6.1 C o n s o l i d a t i o n
Because
of
curves
practical
layer i s studied
considerations
i n a separate
_3
a n n u l a r flume 4.6 10
m
s
t h e c o n s o l i d a t i o n o f t h e sediment
column.
After
severe
of
determined by v i s u a l o b s e r v a t i o n ,
the
sediment-water
i s given
day
interface,
as
i n f i g u r e 13 as a f u n c t i o n o f
t i m e . The c u r v e s a r e measured i n t h e a n n u l a r flume as
column.
i n the
o f t h e sediment s u s p e n s i o n i s brought i n t o t h e
c o n s o l i d a t i o n column. The h e i g h t
settling
mixing
well
as
i n the
The i n t e r f a c e changes 0.007 m i n t h e p e r i o d between 1
and 7 days a f t e r t h e s t a r t o f c o n s o l i d a t i o n , w h i c h i s l e s s
than
31
of t h e t o t a l v a r i a t i o n (- w a t e r d e p t h - bed t h i c k n e s s ) .
6.2 Pore w a t e r p r e s s u r e
The
pore
water
p r e s s u r e i s measured w i t h a t r a n s d u c e r a t t a c h e d
bottom o f t h e s e t t l i n g column. A
prevents
direct
contact
p a r t i c l e s . I n f i g u r e 14
given.
filter
between
i n front
the
t h e water
of
transducer
pressure
the
and
during
transducer
the
s
0
pressure
consolidation
is
distribution.
The
- 1053.8 kg/m*) assuming a h y d r o s t a t i c
fe
ultimate
pressure
also
f o l l o w s from t h e
h y d r o s t a t i c p r e s s u r e ( p - 1020 kg/m*). From f i g u r e 14 i t
w
during
the
first
day
follows
must
value.
be kept i n mind t h a t t h e c o n s o l i d a t i o n p e r i o d s t r o n g l y depends
upon t h e l a y e r
thickness.
6.3 Dry d e n s i t y
profiles
The
i s measured w i t h a probe t h a t d e t e c t s
dry density
an a c o u s t i c s i g n a l due
measuring
that
the water over pressure i s l a r g e l y d i s s i p a t e d .
A f t e r t h r e e days t h e water over p r e s s u r e has reached a c o n s t a n t
The
sediment
The i n i t i a l p r e s s u r e i s a l s o c a l c u l a t e d from t h e b u l k d e n s i t y o f
the s u s p e n s i o n ( c - 56 kg/m , p
It
t o the
technique
to
the
presence
of
the
the a t t e n u a t i o n of
sediment
i s r e c e n t l y made o p e r a t i o n a l a t D e l f t
t r a n s d u c e r s a r e shaped a c c o r d i n g
mass.
The
Hydraulics.
t o small c y l i n d e r s with a
diameter
of 10 mm and a l e n g t h o f 8.5 mm. The v e r t i c a l r e s o l u t i o n i s i n t h e o r d e r
of 3 mm. The
receiver
profile
down
into
measurements a l o w e r i n g
the
i s measured
the
by
sediment
lowering
layer.
the
During
transmitter
the
successive
o f t h e sediment-water i n t e r f a c e i s observed
The
measurements a r e performed d u r i n g
days. From f i g u r e 15 i t i s d e r i v e d
the
at
l o c a t i o n o f t h e measurements. T h i s a f f e c t s m a i n l y t h e c o n c e n t r a t i o n
i n the top l a y e r . A d e t a i l e d d e s c r i p t i o n of the instrument i s given
[7].
and
surface
a c o n s o l i d a t i o n p e r i o d of 7
t h a t a f t e r 1 day t h e d r y d e n s i t y
s
in
near
i s a p p r o x i m a t e l y 110 kg/ra . A f t e r a c o n s o l i d a t i o n p e r i o d o f
- 15 -
3 days t h e d r y d e n s i t y
140
s
kg/m .
near t h e sediment-water i n t e r f a c e i s i n c r e a s e d t o
The d r y d e n s i t y
s
p r o f i l e shows r e l a t i v e l y h i g h v a l u e s , up t o
700 kg/m , near t h e bottom o f t h e column. Because o f
transducers
are
the s i z e
t h e measurements i n t h e upper few m i l l i m e t r e s
unreliable.
of the
of the layer
- 16 -
7. RESULTS ON EROSION
7.1 C r i t i c a l bed s h e a r s t r e s s f o r e r o s i o n
The
concentration-time
the s t a r t o f t h e
c u r v e s d u r i n g e r o s i o n a r e g i v e n i n f i g u r e 16. A t
test
a
background
concentration
of
0.1
kg/m
9
is
p r e s e n t . The e r o s i o n r a t e s a r e c a l c u l a t e d a c c o r d i n g :
c - h g .
(4)
2
with,
c - erosion rate [kg/m /s],
h - w a t e r d e p t h [m],
s
c - suspension
c o n c e n t r a t i o n (depth-averaged) [ k g / m ] ,
t - t ime [ s ] .
The
r e s u l t s are presented
i n f i g u r e 17.
During
t h e e r o s i o n experiment no o r l i t t l e
shear
stress
up
to
erosion
occurs
for a
bed
0.2 Pa. More severe e r o s i o n i s i n i t i a t e d a t a bed
shear s t r e s s o f 0.3 Pa. F i r s t a s m a l l t o p l a y e r w i t h a t h i c k n e s s o f
2 -
3 mm i s eroded. A t t h e end o f t h e s u b t e s t w i t h a bed shear s t r e s s o f 0.4
Pa t h e t o p l a y e r i s c o m p l e t e l y
annular
-0.6
eroded ( a s seen from t h e o u t s i d e
of the
-3
f l u m e ) . The maximum e r o s i o n r a t e s a r e i n t h e o r d e r o f 0.35 10
2
10
kg/m /s. From t h e d e s c r i p t i o n g i v e n above
a
critical
shear
s t r e s s o f 0.2 - 0.3 Pa can be deduced.
7.2 E r o s i o n p a r a m e t e r s
First,
the r e s u l t s of the e r o s i o n experiments are i n t e r p r e t e d according
t o t h e w i d e l y used
g
Equation
shear
and
equation:
- M ( — - 1)
r
e
5 results i n a invariable erosion
(5)
rate
a
constant
bed
s t r e s s i s a p p l i e d . F o r each sub t e s t t h e e r o s i o n r a t e i s averaged
t h e e r o s i o n parameter M i s c a l c u l a t e d . The
results
when
of
the
erosion
rates
c a l c u l a t i o n s a r e g i v e n i n t a b l e 9. I t appears t h a t t h e
v a l u e s f o r t h e e r o s i o n parameter (M) a r e h i g h l y a f f e c t e d by
for the c r i t i c a l
and t h e
shear s t r e s s .
the
choice
- 17 -
c
* 10
max
s
c
* 10
f
s
E
avg
* 10
a
a
[Pa] [kg/m /s] [kg/m /s] [kg/m /s]
a
0.10
0.16
0.20
0.30
0.40
0.50
0.60
0.007
0.011
0.052
0.363
0.537
0.615
0.514
0.001
0.003
0.006
0.028
0.066
0.088
0.090
0.000
0.002
0.002
0.009
0.023
0.037
0.048
M * 10
duration
s
M * 10
s
s
a
[kg/mVs] [kg/m /s]
z -0.20 Pa z -0.30 Pa
e
e
[min]
82
100
94
91
88
95
91
0.056
0.066
0.059
0.045
0.198
0.132
0.090
table 9 - Erosion rates and erosion parameter M
consolidation period: 1 day
e
- maximum erosion rate during sub test
max
_ fj
j
te (averaged over 30 min)
avg
~
^
averaged during sub test
m
QC
Z
As
mentioned
increase
before
i n time
Consequently,
e r o s
e r o s
the
when
also
o n
a
r
o n
a
t
ra
e
suspension
constant
c o n c e n t r a t i o n shows a n o n - l i n e a r
bed
shear
the erosion rate equation
stress
is
as f o r m u l a t e d
applied.
by P a r c h u r e
and Mehta i s used [ 8 ] :
I n ( f - ) - a [z. - t ( z ) ]
E^
b
s
with,
E
P
(6a)
- f l o c e r o s i o n r a t e [kg/m*/s],
F
z ( z ) - bed s t r e n g t h p r o f i l e [ P a ] ,
-6
a
- model parameter [Pa J ,
8
0
- 0.5.
The e r o s i o n depth can be c a l c u l a t e d from the e r o s i o n r a t e p r o v i d e d
the
dry density
profile
i s known.
that
S u b s e q u e n t l y t h e bed s t r e n g t h i s
i n t e r p o l a t e d from t h e bed s t r e n g t h p r o f i l e .
In t h i s
way
a
multi-layer
approach f o r t h e bed i s f o l l o w e d . The s t a t e w i t h f l o c e r o s i o n i s reached
when t h e e r o s i o n has proceeded t o t h e depth where t h e bed
is
equal
to
shear
stress
t h e s t r e n g t h o f t h e bed. A t t h a t stage o c c a s i o n a l l y f l o e s
are removed from t h e bed s u r f a c e r e s u l t i n g i n f l o c
The model parameters a i s e s t i m a t e d
erosion.
from t h e measurements as f o l l o w s . A t
the s t a r t o f s u b t e s t
( i ) t h e s t r e n g t h o f the bed a t t h e s u r f a c e i s e q u a l
to
stress
the
bed
shear
erosion rate at the i n i t i a l
from
the preceding
subtest
s t a t e i s known ( E ) and
0
r a t e i s t a k e n from t h e ' t a i l ' o f the curve o f s u b t e s t
into:
( i - 1 ) . When the
the
floc
erosion
( i ) eq. 6a changes
- 18 -
in
The
( f >- .
(6b)
-
r e s u l t s o f t h e c a l c u l a t i o n s a r e g i v e n i n t a b l e 10.
cons.: 1 day
(7 s u b t e s t s )
P
[Pa
0.50
- f J
]
10.42
table 10 - Erosion
parameters (eg. 6a)
So f a r , no c a l c u l a t i o n s w i t h eq. 6a and parameters
made. T h i s w i l l
from
table
10 a r e
be t h e s u b j e c t o f r e s e a r c h i n 1990.
7.3 G r a i n s i z e . pH and r e d o x - p o t e n t i a l i n t h e s u s p e n s i o n
The
p a r t i c l e s i z e s as measured w i t h t h e M a l v e r n p a r t i c l e s i z e r a r e g i v e n
i n f i g u r e 18. I t f o l l o w s t h a t t h e g r a i n s i z e o f t h e sediment d u r i n g
erosion
suspension
experiment
from
size
of
the
40
original
which
is
h a l f of the i n i t i a l value.
a c i d i t y (pH) d u r i n g t h e e r o s i o n
presented
the g r a i n
(during mixing). This e s p e c i a l l y holds f o r the D ,
approximately
The
differs
the
i n figure
test
i s almost
constant
and i s
19. The measured v a l u e (pH - 7.6) i s c o n s i d e r a b l y
l a r g e r than t h e v a l u e o b t a i n e d by D e l f t G e o t e c h n i c s .
The r e d o x - p o t e n t i a l
i s not measured because no redox probe was a v a i l a b l e a t t h e time.
7.4 P h y s i c o - c h e m i c a l
Two
samples
from
conductivity,
potential
and
p r o p e r t i e s of the suspension
the a n n u l a r flume a r e a l s o a n a l y s e d w i t h r e s p e c t t o
oxygen
and
organic
content,
chlorinity,
pH,
c a t i o n s (see t a b l e 1 1 ) . The f i r s t sample i s t a k e n
redox
during
the m i x i n g p e r i o d p r e c e d i n g t h e e r o s i o n t e s t . The second sample i s t a k e n
during the mixing period f o l l o w i n g the t e s t .
- 19 -
Property of suspension
conductivity
chlorinity
oxygen c o n t e n t
oxygen c o n t e n t
redox-potential
PH
organic content
Na
K
Mg
Ca
Sod. Ads. R a t i o
[mS/cm]
[kg/m»]
[kg/m ]
[X]
[mV]
[-]
[X]
[kg/m']
1 »
1 t
s
[(meq/1)*]
sample 1 sample 2
35.4
18
0.0048
55
+210
7.43
5.2
5.4
0.33
1.00
0.13
35.4
36.1
17
0.0057
65
+ 174
7.04
4.7
5.4
0.34
0.96
0.14
35.9
table 11 - Physico-chemical properties of the
suspension during the erosion experiment.
- 20 -
8. TIDAL EXPERIMENTS
The
concentration-time
c u r v e of the f i r s t t i d a l experiment ( t
i s g i v e n i n f i g u r e 21 ( t i d a l p e r i o d 11).
resulting
in
maximum
suspension
The
erosion
concentrations
e r o s i o n and d e p o s i t i o n r a t e s are p r e s e n t e d
in
depth
of
small
kg/m .
The
maximum
kg/m /s.
the
bed
is
larger
than
0.1
Pa
shear
s t r e s s . When the
bed
commences.
shear s t r e s s lower than t h i s c r i t i c a l v a l u e r e s u l t s i n
A bed
stress
The
shear
( f i g u r e 23) shows t h a t a c r i t i c a l v a l u e e x i s t s f o r the bed
shear
The
2
10
of
Pa)
s
22.
e r o s i o n and d e p o s i t i o n r a t e s are i n the o r d e r of 0.015
stress
is
0.34
figure
graph w i t h the sediment c o n c e n t r a t i o n as a f u n c t i o n
- 0.2
b
erosion
deposition.
The
p a r t i c l e s i z e d u r i n g the t i d a l experiment i s g i v e n i n f i g u r e 24.
comparison w i t h the o r i g i n a l s u s p e n s i o n the D,
i s much s m a l l e r (*•
0
The
p a r t i c l e s i z e does not e x h i b i t a ' t i d a l
D u r i n g the second t i d a l experiment (z
concentration
is
10
kg/m
e r o s i o n t a k e s p l a c e f o r bed
Pa.
Below
this
value
The
mean
sediment
on
when the bed
bed
shear
the
concentration
in
interface
0.06
suspension
the
due
to
The
10-20
the
mm
a
l a y e r and
immediately
During
Waves
the w a t e r
water.
At
show
this
internal
erosion
k g / m / s ) . I n f i g u r e 27 the sediment c o n c e n t r a t i o n
shear s t r e s s .
s
kg/m .
a
and
as
phase
waves
an
rate
(•
with
layer
gradually
l a y e r i s more and more resuspended by
e r o s i o n , w h i c h i s accompanied by a reduced
bed
50
t h i c k n e s s of the f l u i d mud
and
60
( m i x i n g t i m e ) . The maximum
kg/m /s ( f i g u r e 26).
towards
sediment
not
concentration
waves
of
Pa the i n t e r n a l waves break
2
internal
d e c r e a s e s from 40 mm
disappear.
10
0.1
l a y e r f o l l o w s from
shear s t r e s s g r a d u a l l y increases a f t e r s l a c k
e r o s i o n r a t e i s 1.5
erosion
mud
between the f l u i d mud
s t r e s s of a p p r o x i m a t e l y
of
the
thickness
i s i n the o r d e r of 45 -
cause an upward sediment f l u x . T h i s does
increase
little
concentration decreases r a p i d l y .
l a y e r i s formed w i t h a
c o n t i n u i t y c o n s i d e r a t i o n s and
originate
suspension
shear s t r e s s e s lower t h a n a p p r o x i m a t e l y
the
sediment
Pa) the maximum
( f i g u r e 25, t i d a l p e r i o d 11). No or
Around s l a c k w a t e r a f l u i d mud
mm.
30X).
fluctuation'.
- 0.4
b
3
In
surface
-3
0.2
i s p l o t t e d against
10
the
Acknowledgements
This
research
Ministry
of
i s performed
i n commission
of
Rijkswaterstaat (the
T r a n s p o r t and P u b l i c Works o f The N e t h e r l a n d s ) .
p a r t o f "The N e t h e r l a n d s
I n t e g r a t e d S o i l Research Programme".
I t i s also
REFERENCES
[I]
-
Karelse,
M. ,
the a n n u l a r
"Velocity
and
bed s h e a r s t r e s s measurements i n
flume", Z0159-52, D e l f t H y d r a u l i c s , A p r i l 1989
(in
Dutch).
[2]
-
Mehta,
A.J.,
cohesive
sediments",
Engineering,
[3]
-
Krone,
Partheniades,
"The
processes",
In:
-
Vol.
Verreet,
Technical
report
significance
Lecture
G.,
notes
no.
behavior
16,
of
College
of
aggregates to t r a n s p o r t
on
Springer Verlag,
Berlamont,
b e h a v i o u r of sea and
Encyclopedia
of
coastal
14 - E s t u a r i n e c o h e s i v e
A.J. Mehta, 1986,
[4]
"Depositional
U n i v e r s i t y of F l o r i d a , G a i n e s v i l l e , 1973.
R.B.,
studies.
E.,
of
J.,
estuarine
and
estuarine
sediment dynamics.
Ed.
Berlin.
"Rheology
and
mud",
be
to
Non-Newtonian
published
in:
F l u i d Mechanics, V o l . V I I - Rheology of
Non-
Newtonian Flows.
[5]
-
Cornelisse,
J.M.,
K u i j p e r , C. , Winterwerp, J . C ,
and e r o s i o n of C h i n a - c l a y under s t e a d y f l o w " ,
H y d r a u l i c s , A p r i l 1989
[6]
-
Kuijper,
C. ,
deposition
J.M.,
graded c o h e s i v e
the I n t e r n a t i o n a l Symposium on
New
[7]
-
Orleans,
N i j v e l d t , D.,
layers",
august
Z159-51,
Delft
( i n Dutch).
Cornelisse,
of
"Deposition
Winterwerp,
J.C,
"The
s e d i m e n t s " , paper p r e s e n t e d
Sediment
Transport
at
Modeling,
1989.
"Measurements of sediment c o n c e n t r a t i o n s
internal
report,
Delft
Hydraulics,
in
mud
J u l y 1989
(in
Dutch).
[8]
-
Parchure,
T.M.,
Mehta,
A.J.,
"Erosion
of
sediment d e p o s i t s " , J r n l . of H y d r a u l i c Eng.,
Oct.
[9]
-
soft
cohesive
V o l . 111. No.
10,
1985.
Lambe, T.W.,
R.V.
Whitman, " S o i l
mechanics",
Wiley
&
Sons,
1979.
[10]
-
T a y l o r , D.W.,
p a r t 1, pp.
[II]
[12]
-
-
" i o n exchange phenomena", Trans ASCE, V o l .
718-728,
126,
1961.
Committee on T i d a l H y d r a u l i c s , " S o i l as a f a c t o r
in
shoaling
processes,
4,
1960.
Krone, R.B.,
estuarial
a l i t e r a t u r e review",
Techn. B u l l . no.
"Flume s t u d i e s of the t r a n s p o r t
shoaling
processes",
Final
Engineering
Laboratory
and
Sanitary
Laboratory,
University
of
California,
june
1962.
of
sediment
report,
Engineering
Berkely,
in
Hydraulic
Research
California,
Sampling l o c a t i o n .
A4
DELFT
HYDRAULICS
Fig 1
Pcnonil Computer
driving motor
(or upper n n g
^v«w4^^^ve^(Wia\V.
side view (left) and cross-section (right)
Annular flume.
A
DELFT
HYDRAULICS
4
Fig 2
Photographs o f sediment and sediment
particles.
A
DELFT
HYDRAULICS
4
Fig 3
- SEDIMENTATION BALANCE: f l o c c u l a t e d
~° SEDIGRAPH: d i s p e r s e d (1st s a m p l e )
SEDIGRAPH: d i s p e r s e d (2nd s a m p l e )
1 00
90
cc
Ld
<
LJJ
CC
O
UJ
o
<
o
cc
LU
CL
tn
<
1
1
1
—
1
80
1
[
70-
1/
6050
40
•
30
20
\V
10
00.001
1
2
•
t
;
E i
5
0.01
SETTLING
DISTRIBUTION
6 ' t 1
0.1
VELOCITY
f
:i
i
<
1
in
OF SETTLING
1
f c
10
mm/s
VELOCITY
D i s t r i b u t i o n of s e t t l i n g v e l o c i t y ,
A
DELFT
HYDRAULICS
4
Fig 4
SHEAR
RHEOLOGICAL
sensor:
0.0
-T0
1
=
200
K G / M
-
C
=
250
K G / M ?
1
1
1
40
1
1
60
SHEAR
RHEOLOGICAL
sensor:
Rheological
1/s
(CV100)
3
C
1
in
CURVES
UA4D
*
20
RATE
FLOW
1
1
30
RATE
FLOW
1
100
in
1
1
120
1
1
140
1
160
1/s
CURVES
CRV100)
MVil
flow-curves.
DELFT
HYDRAULICS
Fig 5
140.0
40
60
'
SHEAR
RHEOLOGICAL
s e n s o r : MVH
Rheological
80
RATE
FLOW
'
WO
in 1 / s
CURVES
'
120
'
UO
(RV100)
flow-curves.
A
DELFT
HYDRAULICS
Fig
4
b
5
* * * * « Breskens
•
Breskens
(DA45, C V 1 0 0 )
(MEN, RV100)
•
100
-\
—
1
.
o
CL
A
F
•
y
LT)
o
a
^2
'
10
I
—
—
>
7 -—-ryr*'
I
y
c1
)
I
u
—
<
2:
a
—
200
SEDIMENT
0
DYNAMIC VISCOSITY
('downcurve')
300
CONCENTRATION
AS A FUNCTION
400
in k g / r n
OF THE SEDIMENT
500
600
CONCENTRATION
Dynamic v i s c o s i t y o f the sediment.
A4
DELFT
HYDRAULICS
Fig 6
3
SEDIMENT CONCENTRATION in k g / m
YIELD STRESS AS A FUNCTION OF THE SEDIMENT CONCENTRATION
('down curve': intersection of flow curve with vertical axis)
Y i e l d s t r e s s of the sediment.
A4
DELFT
HYDRAULICS
Fig 7
MEASUREMENTS
L O G - N O R M A L FITS
1.00
0.90
-
TIME
C O N C E N T R A T I O N - T I M E C U R V E S DURING
initial c o n c e n t r a t i o n : 0.76
kg/m
in
min
DEPOSITION AND L O G - N O R M A L
FITS
C o n c e n t r a t i o n - t i m e curves d u r i n g d e p o s i t i o n and
log-normal
fits.
A
DELFT
HYDRAULICS
Fig
4
8
1.0
-
0.9
-
0.8
-
0.7
-
0.6
-
\0.5
CT
QJ
° 0.4
-
0.3
-
0.2
-
•
•
o
•
•
•
-
•
ir
• • • • • C
= 0.76
kg/m
iririrttir r e s u s p e n d e d
3
0
0.1
0.0
-
n
0.0
•
B—*
a
.
i
0.1
ii
i1
0.2
0.3
BED SHEAR S T R E S S in
1
1
1
0.4
0.5
Pa
EQUILIBRIUM CONCENTRATION FROM L O G - N O R M A L
n o r m a l i z e d with initial c o n c e n t r a t i o n
FIT
C o n c e n t r a t i o n - t i m e curves d u r i n g d e p o s i t i o n and
log-normal f i t .
A
DELFT
HYDRAULICS
4
Fig 9
60
A A A A A
-
D90
(irvtio! .-clue)
DgQ
• • • • G
D
o o o o o
D,o
5
0
A
A
o
A
M
LO
low
obscuration
A
CJ 20
CC
A
A
A
A
<
CL
D50
•
•
•
1
O
O
•
(iriSol
vai^e)
•
n
O
o
•
DIO (Initial value)
O
O
U
U
o0.10
0.20
BED SHEAR
0.00
SIZE
QUPiN
:XPER!MENT
0.30
STRESS
ON
DEPOSITION
0.40
(C
0
0.50
=
0.76
kg/m"
PART! CI
P a r t i c l e s i z e d u r i n g experiments on d e p o s i t i o n .
A
DELFT
HYDRAULICS
4
F i g 10
3 0
200
TIME
pH
pH
during
experiments
DURING
on
i
n
hours
EXPERIMENT ON DEPOSITION
deposition.
A
DELFT
HYDRAULICS
Fig
4
11
Redox p o t e n t i a l d u r i n g experiments on
deposition.
DELFT
HYDRAULICS
F i g 12
CONSOLIDATION
CONSOLIDATION
CONSOLIDATION
PERiQD
PERIOD
PERIOD
8
6
1
(C046: consolidation column)
DAYS
HOURS (C048: annular flume)
DAY
(C045: annular flume)
iOO
\
V
\
s
\\
\
o
200-
o
CQ
LU
>
o
V.
CQ
<
N
O
100
x
o
Ld
j
o-
4
5 6 '
!3
<
!>
10
SEDIMENT-WATER
i
1 9
100
TIME in
(
•
!
(
i
iI
•>
(
000
' i
0000
min
INTERFACE DURING
Sediment-water i n t e r f a c e d u r i n g
19
CONSOLIDATION
consolidation.
A
DELFT
HYDRAULICS
4
F i g 13
3.14
3.12
-
3.10
J
3.08
-
• • • • • total p r e s s u r e
A A & A A water pressure
calculated initial value (cO = 56
k^/m3)
2.94
0
PORE
1440
WATER
'
2880
4320
PRESSURE
' 5760
' 7200
TIME in min
AND TOTAL P R E S S U R E
'
8640
DURING
0080
11520
CONSOLIDATION
Pore water p r e s s u r e d u r i n g c o n s o l i d a t i o n .
A
DELFT
HYDRAULICS
4
F i g 14
Dry d e n s i t y p r o f i l e s d u r i n g c o n s o l i d a t i o n
( c o n s o l i d a t i o n p e r i o d : 3 days)
A4
DELFT
HYDRAULICS
g 15
C o n c e n t r a t i o n - t i m e curves d u r i n g e r o s i o n
( c o n s o l i d a t i o n p e r i o d : 1 day).
A
DELFT
HYDRAULICS
Fi g
4
16
0.0010
0.0009
—
-
H
EROSION RATE
BED SHEAR S T R E S S
0.0008
0.0007 H
0.60
-^0.0006 H
Pa
I
0.50
UJ 0 . 0 0 0 5
r—
<
rr
0.40
0.0004
z
-
o
o 0.0003 -
0.30
04
UJ
0.20
0.16
0.0002
0.10
0.0001
— i " ^
0.0000
V
v .
0
100
T
200
|
300
1
T
400
500
TIME in min
600
—I
700
r800
EROSION RATE DURING E R G S ' O N EXPERIMENT
c o n s o l i d a t i o n period: 1 day
Erosion rate
(consolidation period:
1 day).
A
DELFT
HYDRAULICS
4
F i g 17
60
5 50 (initial value)
A A A A A
D
9 0
• ••aa D
o o o o o DJO
5 0
40
o
M
CO
y
20
on
<
050
("initial value)
H0
(initio* value)
-e
O-
0.00
0.10
P a r t i c l e s i z e during
period:
0.20
0.30
0.40
0.50
0.60
BED SHEAR S T R E S S in Pa
PARTICLE SIZE DURING EROSION TEST
consolidation period: 1 dcy
erosion
0.70
0.80
(consolidation
1 day).
A
DELFT
HYDRAULICS
4
F i g 18
300_
TfME
oH
pH d u r i n g e r o s i o n
DURING
in
40G
min
EXPERIMENTS
-
ON
500
600
700
EROSION
tests.
A4
DELFT
HYDRAULICS
|Fig 19
250
200 -
>
<
50
LU
I—
o
x 100
o
NO
CL
MEASUREMENTS
PERFORMED
Q
LU
CL
50
0
100
REDOX
Redox p o t e n t i a l
>0
300
POTENTIAL
during
erosion
400
TIME in min
500
DURING EXPERIMENTS
"1
600
ON
r
700
800
EROSION
tests,
A
DELFT
HYDRAULICS
Fig
4
20
0.50
0.50
SEDIMENT CONCENTRATION
BED SHEAR S T R E S S
D e p o s i t i o n and e r o s i o n under t i d a l
(0.2 Pa)
conditions
A4
DELFT
HYDRAULICS
Fig
21
0 50
0.30
0.50
-
0.30
o
0_
O
LU
—
I
<
0.10
-
0.10
$
Ld
cn
on
V—
o
oo
o
CL
CO
-0.10
<
- 0 10
X
CL
CO
LU
Q
LU
CD
Q
X
<
X
-0.30
-
-0.30
o
00
O
CL
Q
-0.50
T
1
i
60
0
|
i
120
!
180
i
I
240
r
I
i
3C0
TIME
i
360
in
i
i
420
i
i
480
i
1
540
1
1
600
1
1
-0.50
r
660
720
min
D E P O S I T I O N - R A T E AND E R O S I O N - R A T E
m a x i m u m bed s h e a r s t r e s s : 0 . 2 P a
UNDER
TIDAL
CONDITIONS
D e p o s i t i o n and e r o s i o n r a t e under t i d a l
conditions
(0.2 Pa)
A
DELFT
HYDRAULICS
4
| F i g 22
0.35
BED
SHEAR S T R E S S
SEDIMENT CONCENTRATION AS A FUNCTION
consolidation period: 6 hours
in
Pc
OF THE BED SHEAR
STRESS
Sediment c o n c e n t r a t i o n v s . bed shear s t r e s s
(0.2 Pa)
DELFT
HYDRAULICS
F i g 23
P a r t i c l e s i z e d u r i n g t i d a l experiment
(0.2
Pa)
A
DELFT
HYDRAULICS
Fig
4
24
DEPOSITION AND EROSION UNDER TIDAL
m a x i m u m bed s h e a r s t r e s s : 0.4 P a
Deposition
(0.4
and
erosion
under t i d a l
CONDITIONS
conditions
Pa)
A
DELFT
HYDRAULICS
Fig
4
25
30.00
0.60
20.00
-0.40
/
o
erosion
CL
O
-0.20
10.00 -
Ul
Ul
LxJ
I—
<
CC
UJ
cc
•0.00
0.00
oo
CL
<
LU
o
CO
o
X
cc
LLJ
- -0.20
-10.00 -
Q
deposition
Q
LU
CO
z
<
O
to
-20.00
P
-
Ul
-0.40
DEPOSITION AND E R c l p l O N - R A T E
BED SHEAR STRESS f
o
Q_
LU
Q
-30.00
-i
1
60
1
1
1
120
1
180
1
1
240
1
1
300
1
1
360
TIME in
|
1
420
i
I
480
i
I
540
i
I
600
i
I
-0.60
r-
660
720
min
DEPOSITION-RATE
AND E R O S I O N - R A T E
m a x i m u m bed shear stress: 0.4
Pa
UNDER
TIDAL
CONDITIONS
D e p o s i t i o n and e r o s i o n r a t e under t i d a l
conditions
(0.4 Pa)
A
DELFT
HYDRAULICS
4
F i g 26
12.00
1 1.00
-
i -|
0.C0
1
1
1
0.04
1
0.08
1
1
1
0.12
1
0.16
BED
1
1
0.20
1
1
SHEAR S T R E S S
SEDIMENT CONCENTRATION AS A FUNCTION
c o n s o l i d a t i o n p e r i o d : 6 hours
Sediment c o n c e n t r a t i o n vs, bed
(0.4
1
0.24
1
0.28
in
1
1
0.32
1
1
0.36
1
1
0.40
Pa
OF THE BED SHEAR
STRESS
shear s t r e s s
Pa)
A4
DELFT
HYDRAULICS
F i g 27
APPENDIX A - DESCRIPTION OF TEST PROGRAM
Al.
Sampling.
a. S e l e c t i o n and d e s c r i p t i o n of the l o c a t i o n .
b. Sample
about 30 kg d r y bed m a t e r i a l (e.g. about 100 kg wet m a t e r i a l )
from a s e d i m e n t a t i o n a r e a w i t h
a
small
"Van
Veen"
grab
sampler;
p r o b a b l y t h e sediments i n a s e d i m e n t a t i o n a r e a a r e r e p r e s e n t a t i v e f o r
the sediments i n the s e l e c t e d l o c a t i o n , whereas i n an
the f i n e r p a r t i c l e s may
layer,
i . e . not
to
obtain
mainly
sediments
cooling
box.
Sample
simultaneously also
this
water
from
the
from one deep p i t . The sediment s h o u l d be
brought ashore as f a s t as p o s s i b l e and t r a n s p o r t e d and
conditions;
area,
have been washed out.
The sampler s h o u l d be s m a l l
surface
eroding
500
can
be
stored
l t r water
under
quiet
transported
and
stored
in
a
weather
in
25 1
jerrycans.
c. D e s c r i b e
the
a r e a and the l o c a l c o n d i t i o n s , t a k e photographs a t t h e
s i t e and of the mud.
Measure the t e m p e r a t u r e , s a l i n i t y ( i f r e l e v a n t )
and oxygen c o n t e n t of the w a t e r , and the redox p o t e n t i a l of the w a t e r
and the
mud.
A2. Determine t h e p h y s i c a l - c h e m i c a l p r o p e r t i e s .
a. The c o m p o s i t i o n of the
mud:
- D e f l o c c u l a t e the mud
and determine the g r a i n s i z e
distribution
w i t h t h e MALVERN and w i t h the s e d i m e n t a t i o n b a l a n c e .
-Determine
the
specific
surface
of
the
mud
(by
Delft
Geotechnics).
-Determine
the
mineralogical
composition
of
the mud
(Delft
Geotechnics).
-Determine
the
o r g a n i c c o n t e n t , the 0
a
c o n t e n t , and the redox
potential.
-Determine the pH, temperature and
-Measure the SAR and CEC
salinity.
(Delft Geotechnics).
-Make some photographs of the sediments w i t h the m i c r o s c o p e .
b. The
p r o p e r t i e s of the
mud:
-Determine the d i s t r i b u t i o n of the s e t t l i n g v e l o c i t y of the
i n the s e d i m e n t a t i o n
-Determine
and
the
yield
balance
up-going
concentrations
(without d e - f l o c c u l e n t ) .
and down-going f l o w curve
strength)
with
of 0 (50)
c
n a t u r a
the
i
Haake-viscometer
Measure
the
vertical
at
kg/n» up t o a s h e a r r a t e of
C. Use
-Determine the c o n s o l i d a t i o n b e h a v i o u r
interface
(viscosity
s
150 s * and a temperature of 20°
the h e i g h t of the
mud
and
dry
the n a t u r a l water.
i n a column by measuring
the
water
density
over
profile
pressure.
within
the
c o n s o l i d a t i o n column w i t h a c o n d u c t i v i t y and/or a c o u s t i c probe
(and measure the vane shear s t r e n g t h a t the end of the t e s t a t
various
depths).
A 3 . Determine the e r o s i o n and s e d i m e n t a t i o n
a. G e n e r a l
behaviour
i n the c a r o u s e l .
t e s t s f o r a l l samples:
-Perform
kg/m
3
a sedimentation
t e s t at an i n i t i a l c o n c e n t r a t i o n of 1
by l o w e r i n g the bed shear
about
0.05
Pa
continued
tests,
the
from
about
the
concentration w i l l w i l l
until
equilibrium
variations
be
measured
in
to
determine
the
organic
attained.
sediment
continuously
taken at r e g u l a r i n t e r v a l s t o c a l i b r a t e the
to
is
suspended
OSLIM ( o p t i c a l c o n c e n t r a t i o n measuring p r o b e ) ;
and
0.40
i n s m a l l s t e p s of about 0 . 0 2 t o 0 . 1 0 Pa. Each
s u b - t e s t w i l l be
During
stress
with
samples w i l l
OSLIM
content
the
and
be
recordings
grain
size
distribution.
-Carry
out
an e r o s i o n t e s t . A s o - c a l l e d d e p o s i t e d bed w i l l
formed i n s t i l l water from the
suspension
deposition
of
a
be
homogeneous
3
of C Q - 6 0 kg/m . A c o n s o l i d a t i o n time of 2 4 hours
( a f t e r s t o p p i n g the a n n u l a r flume) i s used.
The
dry
density
p r o f i l e w i t h i n t h i s bed w i l l be deduced from the c o n s o l i d a t i o n
t e s t d e s c r i b e d above. The
increasing
the
bed
shear
s t e p s of 0 . 0 2 t o 0 . 1 Pa.;
one
hour.
During
e r o s i o n a l behaviour
the
stress
i s determined
from 0 t o about 0 . 7 Pa i n
each s u b - t e s t i s c o n t i n u e d
tests,
the
by
variations
f o r about
i n suspended
sediment c o n c e n t r a t i o n w i l l be measured c o n t i n u o u s l y w i t h
the
OSLIM; samples w i l l be taken at r e g u l a r i n t e r v a l s t o c a l i b r a t e
the OSLIM r e c o r d i n g s and t o determine the o r g a n i c c o n t e n t
grain size
distribution.
and
b. Sediments from n o n - t i d a l l o c a t i o n s ;
Next
to
the t e s t s
mentioned under A3.a. t h e f o l l o w i n g t e s t s
w i l l be performed:
-A s e d i m e n t a t i o n
test
as
described
above
with
an i n i t i a l
3
c o n c e n t r a t i o n o f C Q - 0.2 kg/m .
-An
erosion
t e s t as d e s c r i b e d above w i t h a c o n s o l i d a t i o n time
of 7 days.
c. Sediments f r o m t i d a l l o c a t i o n s :
Next t o t h e t e s t s mentioned under
will
A3.a. t h e f o l l o w i n g
be performed:
-A t e s t w i t h
deposited
a
sinusoidal
bed
amplitude
varying
( s e e A3.a),
h o u r s . The t i d a l
period w i l l
bed
with
a
amount
shear
stress
to
12
hours,
i n suspended
During
and t h e
the t e s t s , the
sediment c o n c e n t r a t i o n w i l l w i l l be
measured c o n t i n u o u s l y w i t h t h e OSLIM; samples w i l l
intervals
to
calibrate
determine the organic content
-A s i m i l a r t i d a l
The
a
c o n s o l i d a t i o n time o f 6
u n t i l e q u i l i b r i u m i s achieved.
variations
regular
on
o f t h e bed s h e a r s t r e s s t o 0.4 Pa. The t e s t w i l l be
continued
A4.
tests
be t a k e n a t
t h e OSLIM r e c o r d i n g s and t o
and g r a i n s i z e
distribution.
t e s t w i t h a shear s t r e s s amplitude
o f 0.2 Pa.
Reporting.
results
and
experimental
data of the composition,
t e s t s w i l l be summarized i n a r e p o r t . These
determine
the c r i t i c a l
results
will
p r o p e r t i e s and
be
used
to
shear s t r e n g t h f o r e r o s i o n and s e d i m e n t a t i o n o f
the mud and i t s e r o s i o n r a t e .
A5. D e t e r m i n a t i o n
Determine
o f t h e f l o c c u l a t i o n p r o p e r t i e s i n t h e s e t t l i n g column
the d i s t r i b u t i o n
of
p r o p e r t i e s a t a g r i d frequency
initial
c o n c e n t r a t i o n s of c
t h e s e t t l i n g v e l o c i t y and f l o c c u l a t i o n
o f 0.05 Hz
(amplitude
-
0.075
m)
and
3
Q
- 0.1 and 0.5 kg/m . Samples w i l l be t a k e n
from 13 l o c a t i o n s o v e r the e n t i r e h e i g h t o f t h e column a t
regular
time
i n t e r v a l s . The s e t t l i n g mud f l o e s w i l l be m o n i t o r e d w i t h a CCD-camera a t
the bottom o f t h e column.
Optical
The
instrument
("OSLItO
c a l i b r a t i o n curve f o r the o p t i c a l i n s t r u m e n t
deposition
i s g i v e n i n f i g u r e B l . During
4
hours a f t e r the s t a r t of the experiment as w e l l as a t the end
of
the experiment on d e p o s i t i o n the o p t i c a l
i s s e t i n p o s i t i o n 1 (low c o n c e n t r a t i o n
B2 the c a l i b r a t i o n curve
of
the
for
min,
instrument
range).
the
erosion
test
is
i s s e t i n two d i f f e r e n t p o s i t i o n s
(2
and
10).
c a l i b r a t i o n c u r v e s f o r the t i d a l e x p e r i m e n t s are g i v e n i n f i g u r e
A l l c a l i b r a t i o n c u r v e s are r e l a t e d t o the 'OSLIM' w i t h a 5 mm
The
c a l i b r a t i o n curve
performed
carried
The
B3.
cell.
i s given i n figure
after
out.
The
B4.
i s d e r i v e d from measurements i n samples w h i c h are
mixed t h o r o u g h l y w i t h a m e c h a n i c a l s t i r r e r f o r some m i n u t e s .
is
the
instrument
c a l i b r a t i o n curve f o r the a c o u s t i c i n s t r u m e n t
The
shown.
i n c r e a s e i n sediment c o n c e n t r a t i o n d u r i n g the t e s t
o p t i c a l instrument
Acoustic
taken
2
In f i g u r e
t - 15 and 30
on
1,
each s u b t e s t . D u r i n g
Because
experiment
the s u b t e s t s samples a r e
(volume: 150 - 200 ml) at v a r i o u s t i m e - s t e p s :
and
f o r the
the
measurements
calibration
curve
i n the c o n s o l i d a t i o n
follows
the
Calibration
column are
semi-logarithmic
r e l a t i o n s h i p as can be d e r i v e d from t h e o r e t i c a l c o n s i d e r a t i o n s [ 7 ] :
U
ln ( z f )
with,
U
(Bl)
- 6 C,
output voltage [ V o l t ] ,
c
U
0
6
o u t p u t v o l t a g e i n c l e a r water
c
d r y d e n s i t y [kg/m*].
constant
[m'/kg],
[Volt]
! .0
e x p e r i m e n t on deposition
s e d i m e n t : Western S c h e l d t
(Breskens);
October
19S9
C a l i b r a t i o n curves o p t i c a l instrument f o r
experiment
on d e p o s i t i o n .
A4
DELFT
HYDRAULICS
Fig Bl
C a l i b r a t i o n curves o p t i c a l instrument f o r
t e s t s on e r o s i o n .
A4
DELFT
HYDRAULICS
l«
g
B2
0.50
0.0034 + 0 03769 V
;0.40
0.30
<
cr
§0.20
0.00
OUTPUT VOLT
..1 V
CALIBRATION CURVE OPTICAL INSTRUMENT 15 m m 'OSLI.M : POSITION
tidal e x p e r i m e n t (ma<. L ^ J s h e a r s'.ress 0.2 P a )
c o n s o l i d a t i o n period: C h v u r s
-
2)
12.00
OUTPUT VOLTAGE in V
CALIBRATION C U R V E OPTICAL INSTRUMENT (5 m m O S L I M ' : POSITION
tidal e x p e r i m e n t ( m a x . bed s h e a r s t r e s s . 0.4 P a )
consolidation period: o hours
10)
C a l i b r a t i o n curves o p t i c a l instrument f o r
tidal
experiments.
A4
DELFT
HYDRAULICS
Fig
B3