Geoscience Reference
In-Depth Information
can be expressed as
k
1
C
n
0
<
C
≤
C
p
ω
sf
=
(11.2)
)
β
ω
(
1
−
k
2
C
C
>
C
p
s
0
m
−
3
;
where
C
is the sediment concentration in kg
·
ω
s
0
is a reference settling velocity;
n
,
,
k
1
, and
k
2
are coefficients; and
C
p
is the sediment concentration at which the
floc settling velocity turns from an increasing to a decreasing trend in the curve of
ω
sf
β
s
−
1
, and
∼
C
.
k
1
=
0.513,
k
2
=
0.008,
n
=
1.29,
β
=
4.65,
ω
=
0.0026 m
·
s
0
m
−
3
for the curve in Fig. 11.5. However, many experiments have shown
that these parameters depend on sediment properties.
n
ranges from 1 to 2 with a
mean value of 1.3, while
C
p
=
·
3.5 kg
β
ranges between 3 and 5. Huang (1981) evaluated
C
p
as
m
−
3
for the Lianyun Harbor mud, and Li
et al
. (1994) gave
C
p
a value
about 1.5 kg
·
m
−
3
for the Gironde Estuary mud.
of 3.0 kg
·
Salinity
As observed by Krone (1962), Owen (1970), Huang (1981), and Yue (1983), salinity
influences flocculation significantly. Most clay particles have a negative charge. In fresh
water, the electrokinetic potential associated with the particles generally is sufficiently
large, and as a result, the particles will repel each other. However, in saline water,
this potential is reduced below a critical value, the electrical layer associated with the
particles collapses; thus, the particles stick together to form flocs, due to the presence of
dominating molecular attractive forces (London-Van der Waals forces), electrostatical
surface forces (double layer), and chemical forces (hydrogen bonds, cation bonds, and
cementation).
Chien and Wan (1983) presented a graphical relation of floc settling velocity and
salinity, which is shown in Fig. 11.6. It can be seen that when salinity is low, the floc
Figure 11.6
Settling velocity as function of salinity (Chien and Wan, 1983).
