Environmental Engineering Reference
In-Depth Information
Hydraulic radius R = 4 m
15
Dunes
10
Dunes
Mega-ripples
5
Fr = 0.16
Fr = 0.12
Fr = 0.08
Ripples
0
1
5
10
15
Particle parameter D
*
Hydraulic radius R = 0.5 m
15
Dunes
10
Dunes
Mega-ripples
Fr = 0.15
Fr = 0.25
Fr = 0.35
5
Ripples
Figure 5.6. Classification of
bed forms according to van Rijn
(1984c) and expected bed forms
in irrigation canals.
0
Fr = 0.45
1
5
10
15
Particle parameter D
*
The total effective shear stress (
τ
) can be separated into two parts,
namely that due to skin resistance
τ
and form resistance
τ
:
τ
+
τ
τ
=
(5.15)
Similar to the separation of shear stress in grain and form resistance,
the Nikuradse's equivalent sand roughness height
k
se
can be separated as
(van Rijn, 1982):
k
s
+
k
s
k
se
=
(5.16)
where
k
s
=
roughness due to grain (m)
k
s
=
roughness due to bed form development (m)
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