Geoscience Reference
In-Depth Information
Table 3.5
Coefficients of the Ackers-White formula
D
∗
≥
60
1
<
D
∗
<
60
n
=
0.0
n
=
1.00
−
0.56 log
D
∗
A
c
=
0.23
D
−
1
/
2
A
c
=
0.17
+
0.14
∗
m
=
9.66
D
−
1
∗
m
=
1.50
+
1.34
=
0.025
log
=−
3.53
+
2.86 log
D
∗
−
(
log
D
∗
)
2
Many tests have shown that the Ackers-White formula overpredicts the transport
rate for fine sediments (smaller than 0.2 mm).
3.6.2 Fractional transport rate of bed-material load
Modified Ackers-White formula (Day, 1980; Proffitt and Sutherland, 1983)
Day (1980) and Proffitt and Sutherland (1983) extended the Ackers-White (1973)
formula to calculate the fractional bed-material load transport rate:
F
gr
,
k
A
c
−
1
m
G
gr
,
k
=
(3.111)
where
U
√
32 log
1
−
n
U
U
n
U
n
C
t
∗
k
h
p
bk
d
k
γ
∗
F
gr
,
k
=
η
k
,
G
gr
,
k
=
[
(γ
/γ
−
1
)
gd
k
]
1
/
2
/γ
(
10
h
/
d
k
)
s
s
with
C
t
∗
k
being the sediment concentration by weight of size class
k
, and
η
k
the hiding
and exposure correction factor. Day's correction factor is
1
η
k
=
(3.112)
0.4
(
d
k
/
d
A
)
−
0.5
+
0.6
where
d
A
is the reference diameter, determined by
1.6
d
84
d
16
−
0.28
d
A
d
50
=
(3.113)
Proffitt and Sutherland's correction factor reads
⎧
⎨
d
k
/
d
u
≤
0.40,
0.075
η
k
=
0.53 log
(
d
k
/
d
u
)
+
1.0, 0.075
<
d
k
/
d
u
≤
3.7
(3.114)
⎩
1.30,
d
k
/
d
u
>
3.7
where
d
u
is the reference diameter used by Proffitt and Sutherland (1983).
