Claessens, J.

De Mulder, T.

Meersschaut, Y.

Mostaert, F.

van Pagee, J.A.

Wang, Z.B.

Winterwerp, J.C.

Open Marine Archive

LTV Westerschelde 1
nr. 1
morphological changes in the
Scheldt estuary and its
consequences on hydrodynamics
J.C. Winterwerp, Z.B. Wang,
J.A. van Pagee, F. Mostaert,
Y. Meersschaut, T. de Mulder &
J. Claessens
LTV Westerschelde 2
nr. 2
contents
• some historical development,
• development of primary tidal movement,
• sediment balance,
• morphodynamic processes, with emphasis:
•tidal asymmetry, and
•compound channels
• application to Scheldt estuary.
LTV Westerschelde 3
nr. 3
historical developments (1)
• reduction of Western Scheldt basin,
• reclamation along Sea Scheldt,
• controlled flood areas (GOG’s),
• mean water levels
LTV Westerschelde 4
nr. 4
historical developments (2)
loss of tidal volume, af er van der Spek, 1994
LTV Westerschelde 5
nr. 5
historical developments (3)
developments around Antwerp
LTV Westerschelde 6
nr. 6
historical developments (4)
controlled flood areas (GOG’s) along Scheldt estuary (533 ha)
LTV Westerschelde 7
nr. 7
primary tidal movement (1)
evolution of HW     LW      tidal amplitude
since 1900
Antwerp
Dendermonde
Flushing
LTV Westerschelde 8
nr. 8
primary tidal movement (2)
• considerable changes in tidal amplitude &
water levels,
• also: increase in celerity tidal wave, hence a
decrease in phase difference Flushing -
Antwerp (next sheet),
• hence an increase in tidal volume (more
efficient tidal filling),
• feed-back to morphological developments.
LTV Westerschelde 9
nr. 9
primary tidal movement (3)
station time lag HW
w.r.t. Flushing
time lag LW
w.r.t. Flushing
Terneuzen - 5 min. - 2 min.
Bath - 10 min.
(~ 5 deg.)
- 11 min.
change in time lag water levels
wit respect to Flushing from 1960 to 1990
(MOVE report 1, 1997)
LTV Westerschelde 10
nr. 10
sediment balance (1)
• maintenance dredging:
•Western Scheldt: about   13 Mton/yr
•Sea Scheldt: about 2- 3 Mton/yr
• sand mining WS: about  3.5 Mton/yr
• sand import: about     1 Mton/yr (?)
so human interference is large
LTV Westerschelde 11
nr. 11
sediment balance (2)
0
5
10
15
20
1
9
5
5
1
9
5
8
1
9
6
1
1
9
6
4
1
9
6
7
1
9
7
0
1
9
7
3
1
9
7
6
1
9
7
9
1
9
8
2
1
9
8
5
1
9
8
8
1
9
9
1
1
9
9
4
1
9
9
7
year
d
r
e
d
g
i
n
g
 
v
o
l
u
m
e
 
[
M
t
o
n
]
deepening 1970 deepening 97/98
maintenance dredging in Western Scheldt
LTV Westerschelde 12
nr. 12
morphodynamic processes
• tidal pumping,
• gravitational circulation,
• meandering thalweg,
• circulations in multiple channel system
(ebb-flood channels),
• flooding and drying on intertidal areas,
• tidal asymmetry,
• compound channels.
LTV Westerschelde 13
nr. 13
tidal asymmetry (1)
• overtides (e.g. M4 vs M2) because of non-linear
processes (advection, friction):
• relative amplitude ratio:
• relative phase difference:
• P > 0  flood dominant, P < 0  ebb dominant
• see example graphs next sheet
• for fine sediments: slack period
u t u t0
2
0
20 5 1 2cos . cosω ωb gc h b g 
A a
a
a
aII I

F
HG
I
KJ
F
HG
I
KJ
4
2
4
2
P II I   2 22 4 2 4ϕ ϕ ϕ ϕb g b g
LTV Westerschelde 14
nr. 14
tidal asymmetry (2)
a2 = 1 m, a4 = 0.25 m
-2
-1
0
1
2
0 5 10 15 20 25
time
w
a
t
e
r
 
l
e
v
e
l
P =  -20 deg
P = +20 deg
short flood & rapid rising tide, hence
large u and flood dominant
long flood, hence ebb dominant
h = a2cos{t} + a4cos{2 (t-t)}
LTV Westerschelde 15
nr. 15
compound channels (1)
Ac
As As
bt
Ac (= Vc) = flow carrying cross section,
As (= Vs) = storage area, e.g. flood plains
bt            = total width
celerity tidal wave c = Acg/bt
LTV Westerschelde 16
nr. 16
compound channels (2)
after Speer et al., 1991
LTV Westerschelde 17
nr. 17
compound channels (3)
Ac
As As
bt
both changes lead to an increase in ebb-dominancy 
in tidal channel !!
increasing depth:
c increases, and
a/h decreases
increasing storage:
c decreases, and
Vs/Vc increases
LTV Westerschelde 18
nr. 18
asymmetry in Western Scheldt (1)
Doel
LTV Westerschelde 19
nr. 19
asymmetry in Western Scheldt (2)
1950 1960 1970 1980 1990 2000
-20
-10
0
10
20
30
40
c
u
m
u
l
a
t
i
v
e
 
b
u
d
g
e
t
 
c
h
a
n
g
e
 
(
M
m
3
)
NAP+3.5m
NAP-2m
Central part - sections 3 and 4
29
31
1950 1960 1970 1980 1990 2000
-80
-60
-40
-20
0
20
c
u
m
u
l
a
t
i
v
e
 
b
u
d
g
e
t
 
c
h
a
n
g
e
 
(
M
m
3
)
NAP+3.5m
NAP-2m
Eastern part - sections 1 and 2
-4
-56
1950 1960 1970 1980 1990 2000
-40
-30
-20
-10
0
10
20
30
c
u
m
u
l
a
t
i
v
e
 
b
u
d
g
e
t
 
c
h
a
n
g
e
 
(
M
m
3
)
NAP+3.5m
NAP-2m
Western part - sections 5 and 6
-12 -18
morphological development:
evolution of sediment
volume in WS shows large 
erosion in eastern part and 
accretion in central part
LTV Westerschelde 20
nr. 20
asymmetry in Western Scheldt (3)
1970 1975 1980 1985 1990 1995 2000
Year
0.055
0.06
0.065
0.07
0.075
0.08
a
m
p
l
i
t
u
d
e
 
r
a
t
i
o
 
M
4
 
t
o
 
M
2
Vlissingen
Terneuzen
Hansweert
Bath
1970 1975 1980 1985 1990 1995 2000
Year
-30
-20
-10
0
10
20
30
40
p
h
a
s
e
 
d
i
f
f
e
r
e
n
c
e
 
2
M
2
-
M
4
1970 1975 1980 1985 1990 1995 2000
Year
0.8
0.85
0.9
0.95
1
1.05
1.1
A
 
(
-
)
Terneuzen/Vlissingen
Hansweert/Terneuzen
Bath/Hansweert
1970 1975 1980 1985 1990 1995 2000
Year
-30
-20
-10
0
10
20
30
40
50
60
P
 
(
-
)
Terneuzen/Vlissingen
Hansweert/Terneuzen
Bath/Hansweert
large changes 
in eastern part:
at Bath:
less flood dom.
at Hansweert:
less ebb dom. 
LTV Westerschelde 21
nr. 21
asymmetry in Western Scheldt (4)
1 2 3 4 5 6
echo-sounding area
0
0,05
0,1
0,15
0,2
0,25
a
/
h
1955
1996
1 2 3 4 5 6
echo-sounding area
0
0,02
0,04
0,06
0,08
0,1
0,12
V
s
/
V
c
1955
1996
-0,05 -0,04 -0,03 -0,02 -0,01 0 0,01 0,02
change of a/h
-40
-30
-20
-10
0
10
c
h
a
n
g
e
 
o
f
 
P
1+2
3+4
5+6
-0,05 -0,04 -0,03 -0,02 -0,01 0 0,01 0,02
change of Vs/Vc
-40
-30
-20
-10
0
10
c
h
a
n
g
e
 
o
f
 
P
5+6
1+2
3+4
development in bathymetry (hypsometry) has 
strong effect on tidal a ymmetry 
LTV Westerschelde 22
nr. 22
conclusions (1)
• large natural and human-induced
developments of Scheldt morphology,
• strong increase in high waters and tidal
amplitude, probably as a result of widening
and deepening of the channels,
• large-scale feed-back to morphological
developments because of more efficient tidal
filling (though changes in tidal volume could
not be measured because of accuracy),
• historical morphological changes have
affected tidal asymmetry strongly, and are
reasonably understood,
LTV Westerschelde 23
nr. 23
conclusions (2)
• this does not imply that interaction tidal
asymmetry - morphology is fully understood,
• in particular: sequence
horizontal asymmetry 
vertical asymmetry 
residual flow
not yet fully understood,
• however, analysis of tidal asymmetry is strong
tool for sustainable management of the
estuary:
LTV Westerschelde 24
nr. 24
developing the Scheldt estuary
through sustainable management


Morphological changes in the Scheldt estuary and its consequences on hydrodynamics [PRESENTATION]

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