Geoscience Reference
In-Depth Information
Figure 3.22
Relation of fractional suspended-load transport rate (Wu
et al
., 2000b).
3.6 BED-MATERIAL LOAD TRANSPORT
Bed-material load is the sum of bed load and suspended load. Therefore, one may
either separately calculate the bed-load and suspended-load transport rates, or directly
calculate the bed-material load transport rate. Examples of the former approach are
the methods of Einstein (1950), van Rijn (1984a & b), and Wu
et al
. (2000b), which
are introduced in Sections 3.4 and 3.5. Examples of the latter approach are Laursen's
(1958), Engelund and Hansen's (1967), Ackers and White's (1973), Yang's (1973),
and Karim's (1998) methods, which are introduced below.
3.6.1 Total transport rate of bed-material load
Laursen formula
The Laursen (1958) formula divides a sediment mixture into size classes and calculates
the total average concentration of bed-material load as
p
k
d
k
h
7
/
6
τ
b
1
f
U
∗
ω
sk
N
C
t
∗
=
γ
τ
ck
−
0.01
(3.103)
k
=
1
where
C
t
∗
is the sediment concentration by weight per unit volume;
p
k
is the fraction
of the
k
th size class of available sediment material;
N
is the total number of size classes;
τ
ck
is the critical shear stress for the incipient motion of sediment size
d
k
, given by the
Shields diagram; and
τ
b
is the bed shear stress due to grain roughness, determined
