Environmental Engineering Reference
In-Depth Information
d
50
=
median diameter (m)
specific density of the sediment particle (dimensionless)
Excess bed shear stress parameter (
T
) is defined as:
s
=
τ
−
τ
cr
T
=
(3.17)
τ
cr
where:
τ
cr
=
critical shear stress according to Shields (N/m
2
)
grain shear stress (N/m
2
), which is the skin resistance or the surface
drag due to the grain roughness (see Chapter 5 for more details)
The particle Reynolds number parameter (Re
∗
) is represented by
τ
=
u
∗
d
50
ν
Re
∗
=
(3.18)
where:
u
∗
=
shear velocity (m/s)
d
50
=
median diameter (m)
kinematic viscosity (m
2
/s)
Transport rate parameter (
φ
) is represented by:
ν
=
q
s
=
φ
(3.19)
1)
0
.
5
g
0
.
5
d
1
.
5
50
(
s
−
where:
q
s
=
volumetric sediment transport rate (m
3
/s per m width)
s
=
specific density of sediment (dimensionless)
acceleration due to gravity (m/s
2
)
g
=
d
50
=
median diameter (m)
The concentration (
C
) is the ratio between the sediment transport rate
q
s
and the discharge
q
per m width (both in volume). Here,
q
s
is the volume
of sediment transported in 1 m
3
of water-sediment mixture. The volumetric
concentration reads as:
q
s
q
C
=
(3.20)
where:
C
=
concentration of sediment in the water by volume (percentage
or ppm)
volumetric sediment transport rate (m
3
/s per
m
width)
q
s
=
discharge (m
3
/s per
m
width)
q
=
ppm
parts per million
The concentration
C
can be also expressed as a percentage by mass
(
C
g
), which is the mass of sediment transported in a unit volume of a
=
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