Environmental Engineering Reference
In-Depth Information
Table 5.9. Value of a and b for different z/h 0 (Galappatti, 1983).
a 1
b 1
a 2
b 2
a 3
b 3
a 4
b 4
z/h 0 = 0.01
6.321
T A
1.978
0.000
0.000
3.256
0.000
0.193
0.000
L A
6.325
3.331
1.978
0.543
3.272
0.400
0.181
1.790
z/h 0 =
0.02
T A
1.788
0.000
5.779
0.000
2.860
0.000
0.226
0.000
L A
1.789
0.570
5.783
3.000
2.872
0.560
0.217
1.430
z/h 0 =
0.05
T A
1.486
0.000
4.999
0.000
2.306
0.000
0.247
0.000
L A
1.486
0.576
5.002
2.416
2.314
0.720
0.242
0.910
For a steady sediment flow ( c/ ∂t
=
0):
L A ∂c
∂x
c e
c
=
(5.132)
After integration the equation results in:
c 0 )exp
x
L A
c
=
c e
( c e
(5.133)
In the introduction it was mentioned that the rates of suspended load
and bed load transport of particles larger than 0.3 mm are comparable
and the more reliable sediment transport predictors in irrigation canals
compute the total load (suspended and bed load). For this reason it will be
essential to consider the sediment transport in non-equilibrium conditions
as a whole. Although the bed load reacts instantaneously from a non-
equilibrium condition to an equilibrium condition, it is assumed that the
characteristic adaptation length for the bed load is the same adaptation
length as for suspended load. Therefore, the total sediment transport under
non-equilibrium conditions can be described by using the total sediment
concentration (bed and suspended load) instead of a suspended sediment
concentration.
This leads to:
c 0 )exp
x
L A
c
=
c e
( c e
(5.134)
A detailed study of Galappatti's model was made by Ghimire (2003),
Ribberink (1986) and Wang et al. (1986). Their research showed that there
are certain limitations to this model, which most notably are:
the error in the solution increases once the mean concentration moves
relatively far away from the mean equilibrium concentration:
c e
c
1
(5.135)
c
The solution is valid when the deviation of C from C e is in the range of
0 to 50%;
 
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