Of the 99 flocs which constituted the total population, 63 aggregates fell
within the microfloc size classification (fig. 3a). There was a single large
macrofloc. The floc shape (fig. 3b) could be seen to be near-spherical
throughout the entire size range. The macrofloc size bands demonstrated
setding ratcs of the order of 1-3.5 mm s
1 (fig. 3c), whereas the microflocs
of size bands 1-3 had Ws of 0.09-0.5 mm s '. The complementary effective density plot of figure 3d showed that the macroflocs had effective
densities as low as 27 kg nr 3 , with the smaller flocs having mean size
band effective densities of 140-160 kg m -3 .
The fractal dimension, nf, of each floc was estimated by equation 3.2
which was proposed by Winterwerp (1997), based on research by
Kranenburg (1994). It assumes that flocculated mud can be represented
bv a self-similar fractal stmcture:
W s = α’ D
p
3-nf [(ρ
sed
- ρ
w
) g] / μ D nf-1
3.2
where p se d was the sediment mean densitv; g and p are the acceleration
due to gravity and molecular viscosity, respectively. It was assumed that
the ptimary particle diameter (Dp) = 4 pm and the empirical coefficient
(α') = 0.05. Figure 3e indicates that the sample fractal dimensions ranged
between 1.95-2.25. Figure 3f highlights the very high porosity, 90-98.3%,
of the macroflocs. These flocs would be very fragile and easily broken-up
by increasing turbulent shear, in comparison to the stronger less porous
(75-84%) microflocs.
The unique sampling technique of the Inssev system allows the floc sample to be referenced to the ambient SPM, and hence floc dry mass (fig. 3g)
to be apportioned accordingly. The ratio of filtered to Inssey determined
SPM of sample 7 was 1.05 which indicates statistically that the computed
Inssev floc descriptors are representative of the ambient in situ floc
population. Figure 3h shows the division of SPM, and figure 3i the mass
settling flux computed for each size band as the product of the Ws and
SPM. Interestingly, 56.5% of the total mass concentration was contained
within the macrofloc range, however this constituted 77.5% of the effective mass settling flux.
233
within the microfloc size classification (fig. 3a). There was a single large
macrofloc. The floc shape (fig. 3b) could be seen to be near-spherical
throughout the entire size range. The macrofloc size bands demonstrated
setding ratcs of the order of 1-3.5 mm s
1 (fig. 3c), whereas the microflocs
of size bands 1-3 had Ws of 0.09-0.5 mm s '. The complementary effective density plot of figure 3d showed that the macroflocs had effective
densities as low as 27 kg nr 3 , with the smaller flocs having mean size
band effective densities of 140-160 kg m -3 .
The fractal dimension, nf, of each floc was estimated by equation 3.2
which was proposed by Winterwerp (1997), based on research by
Kranenburg (1994). It assumes that flocculated mud can be represented
bv a self-similar fractal stmcture:
W s = α’ D
p
3-nf [(ρ
sed
- ρ
w
) g] / μ D nf-1
3.2
where p se d was the sediment mean densitv; g and p are the acceleration
due to gravity and molecular viscosity, respectively. It was assumed that
the ptimary particle diameter (Dp) = 4 pm and the empirical coefficient
(α') = 0.05. Figure 3e indicates that the sample fractal dimensions ranged
between 1.95-2.25. Figure 3f highlights the very high porosity, 90-98.3%,
of the macroflocs. These flocs would be very fragile and easily broken-up
by increasing turbulent shear, in comparison to the stronger less porous
(75-84%) microflocs.
The unique sampling technique of the Inssev system allows the floc sample to be referenced to the ambient SPM, and hence floc dry mass (fig. 3g)
to be apportioned accordingly. The ratio of filtered to Inssey determined
SPM of sample 7 was 1.05 which indicates statistically that the computed
Inssev floc descriptors are representative of the ambient in situ floc
population. Figure 3h shows the division of SPM, and figure 3i the mass
settling flux computed for each size band as the product of the Ws and
SPM. Interestingly, 56.5% of the total mass concentration was contained
within the macrofloc range, however this constituted 77.5% of the effective mass settling flux.
233