Geoscience Reference
In-Depth Information
Table 2.1
Density and viscosity of water
Temperature (
◦
C)
Density (kg
·
m
−
3
)
Dynamic viscosity (N
·
s
·
m
−
2
)
Kinematic viscosity (m
2
s
−
1
)
1.79
×
10
−
3
1.79
×
10
−
6
0
1000
1.51
×
10
−
3
1.51
×
10
−
6
5
1000
1.31
×
10
−
3
1.31
×
10
−
6
10
1000
15
999
1.14
×
10
−
3
1.14
×
10
−
6
1.00
×
10
−
3
1.00
×
10
−
6
20
998
8.91
×
10
−
4
8.94
×
10
−
7
25
997
7.97
×
10
−
4
8.00
×
10
−
7
30
996
7.20
×
10
−
4
7.25
×
10
−
7
35
994
40
992
6.53
×
10
−
4
6.58
×
10
−
7
The kinematic viscosity of water,
ν
, is the ratio of the dynamic viscosity to the
water density:
ν
=
µ
ρ
f
(2.3)
m
−
2
and m
2
s
−
1
, respectively.
Water viscosity is directly related to molecular interactions. It decreases as water
temperature increases, as shown in Table 2.1. For common temperatures in rivers, the
kinematic viscosity can be approximated by
The units often used for viscosities
µ
and
ν
are N
·
s
·
0.00116
T
2
0.0000102
T
3
10
−
6
m
2
s
−
1
ν
=
(
1.785
−
0.0584
T
+
−
)
×
(2.4)
where
T
is the temperature in
◦
C (degrees Celsius).
2.1.2 Properties of sediment
2.1.2.1 Physical properties of single particles
Density and specific weight of sediment
Sediment density,
m
−
3
.
It depends on the material of sediment. The density of quartz particles is about
2,650 kg
ρ
s
, is the mass of sediment per unit volume, often in kg
·
m
−
3
and does not vary significantly with temperature. Inmost natural rivers,
the density of sediment can be assumed to be constant.
The specific weight of sediment,
·
γ
s
, is the weight of sediment per unit volume, often
m
−
3
. It is related to the sediment density by
in N
·
γ
=
ρ
s
g
(2.5)
s
Due to the buoyancy effect, the specific weight of sediment particles submerged in
water is lighter than the actual specific weight exposed to air. According to Archimedes'
principle, the specific weight of submerged sediment is the difference between the
specific weights of sediment and water,
γ
s
−
γ
f
.
