=
specific gravity of the bed material
Ss
Ds
=
Size of bed material, m, ft
y
=
Depth of flow, m, ft
n
=
Manning's roughness coefficient
The following values for Ku in Equation 3.48 can be obtained:
Metric (SI) Units (m)
Using Ks = 0.039, Ss = 2.65, Knu = 0.041
Ku = 6.19
English Units (ft)
Using Ks = 0.039, Ss = 2.65, Knu = 0.0336
Ku = 11.25
Critical Size for the Beginning of Bed Material Movement. Rearranging Equation 3.48 to give
the critical bed material size Ds for beginning of motion for velocity V, depth y, Shield's
parameter and Manning's n results in:
Ku V3
Dc =
(3.50)
1/ 2
y
1
Ku =
= 0.0042
(SI)
6.19 3
1
Ku =
= 0.0007
(English)
11.25 3
Depth of Flow For No Bed Material Movement as a function of V and D. Equation 3.48 can
be solved, for the depth y for no bed material movement for a given velocity, specific density,
size of bed material, Shields parameter and bed roughness. This equation is useful to
determine clear water-scour at a contraction. This is particularly true if the velocity is
converted to discharge using the continuity equation.
K yu V 6
V6
y=
=
(3.51)
K u D2
6
D2
s
s
K yu = 1.78 x 10 -5
(SI)
K yu = 4.94 x 10 -7
(English)
3.42
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