Geoscience Reference
In-Depth Information
long, starting from the mouth to the Garonne and Dordogne Rivers (see Fig. 11.13).
The computational mesh was uniform, with a size of 500m
250m for each cell.
The tidal flow and cohesive sediment transport during May 19-22, 1974 were sim-
ulated. To consider the effect of salinity on sediment flocculation, salinity transport
was also simulated using the depth-averaged 2-D model introduced in Section 12.1.
The computational time step was 30 minutes.
The sediment parameters were selected carefully, according to suggestions of Li
et al
.
(1994). For the sand bottom, extending from the estuary mouth to about 15 km
upstream from Royan,
×
m
−
2
, and for the reach covered by
τ
ce
was set to be 2.0 N
·
m
−
2
.
M
was given
cohesive sediments,
τ
ce
was given values between 1.3 and 1.5 N
·
m
−
2
.
Because only a few days of sediment transport were simulated, the consolidation pro-
cess was not considered. The settling velocity was calculated using Eq. (11.9). For
the correction factor of sediment diameter in Eq. (11.10),
n
d
m
−
2
s
−
1
.
0.002 kg
·
τ
bd
,min
was set as zero, and
τ
bd
,max
was prescribed as 0.3 N
·
0.022
mm, which were calibrated using Migniot's measurement data. The parameters in the
correction factor of sediment concentration in Eq. (11.11) were
k
1
=
=
1.8 and
d
r
=
2.5,
k
2
=
0.008,
m
−
3
,
n
C
p
4.65, which were used by Li
et al
. (1994) except
that the value of
k
1
was adjusted accordingly. For the correction factor of salinity in
Eq. (11.12),
n
sa
=
3.0 kg
·
=
1.3, and
r
=
m
−
3
. For the correction factor of
=
·
0.5 and
C
sap
was given 30 kg
m
−
2
,
n
t
1
and
n
t
2
were 0.165,
turbulence shear in Eq. (11.13),
τ
p
was given 0.17 N
·
and
k
t
1
was 1.5.
Fig. 11.14 shows the simulated flow fields in flood and ebb tides, and Fig. 11.15
shows the simulated and measured water levels and velocities. The amplitudes and
phases of water level and velocity were predicted well by the numerical model. No
obvious phase difference existed between measurement and simulation. Fig. 11.16
shows the sediment transport rate per unit cross-sectional area, i.e.,
UC
, the product
of flow velocity and sediment concentration. The simulated sediment transport rates
match the measured data generally well.
Figure 11.14
Calculated flow patterns in Gironde Estuary (Wu and Wang, 2004c).
