Environmental Engineering Reference
In-Depth Information
The factor
α
will be determined for each of the three sediment transport
predictors.
•
The exponent
N
in the Engelund-Hansen predictor is constant and is 5.
The correction for this predictor is a function of the
B
/
y
ratio and side
slope
m
. The correction is for:
1
.
2785(
B/h
)
−
0
.
0937
m
0
.
078
trapezoidal canal:
α
s
=
(5.107)
1
.
2(
B/h
)
−
0
.
0663
rectangular canal:
α
s
=
(5.108)
•
In the Ackers-White predictor the correction factor
α
is a function of
the
B
/
y
ratio, velocity exponent
N
, side slope
m
and sediment size
d
50
.
For the analysis the sediment size
d
50
is replaced by the dimensionless
grain parameter
D
and the exponent
N
varies from 3 to 10. All the
other hydraulic and sediment characteristics are the same as for the
Engelund-Hansen predictor. Using a non-linear regression analysis
the correction factor
α
can be given by:
trapezoidal canal:
α
s
=
0
.
396(
B/h
)
−
0
.
1012
N
0
.
7514
m
0
.
0541
(log
D
∗
)
0
.
2427
(5.109)
0
.
0868(
B/h
)
−
0
.
1699
N
1
.
3175
D
0
.
3153
∗
rectangular canal:
α
s
=
(5.110)
•
The correction factor for the Brownlie predictor is a function of the
B
/
y
ratio, velocity exponent
N
and side slope
m
. The exponent
N
varies
from 3 to 6. All the other hydraulic and sediment characteristics are the
same as for the Engelund-Hansen predictor. A non-linear regression
analysis gives the following correction factor
α
for:
trapezoidal canal:
α
s
=
1
.
023(
B/h
)
−
0
.
0898
N
0
.
1569
m
0
.
078
(5.111)
0
.
8492(
B/h
)
−
0
.
0361
N
0
.
2106
rectangular canal:
α
s
=
(5.112)
5.3.8
Predictability of the predictors with the correction factor
Literature presents several procedures that have been developed to com-
pute the total sediment discharge in open channels and here they will be
named procedures 1, 2 and 3.
◦
Procedure 1
: the sediment discharge per unit width (
q
s
) is calculated
by using the hydraulic radius
R
as the characteristic variable for the
water flow. The average width represents the canal width and the
total sediment transport is determined by the multiplication of these
variables:
Q
s
=
q
s
B
av
with
q
s
=
f
(
R
)
(5.113)
◦
Procedure 2
: the sediment transport per unit width (
q
s
) is calculated
by using the water depth as the characteristic variable. Next, the
total sediment transport
Q
s
is calculated by multiplying the sediment
transport per unit width (
q
s
) and the bottom width
B
:
Q
s
=
q
s
B
av
with
q
s
=
f
(
h
)
(5.114)
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