Environmental Engineering Reference
In-Depth Information
the table. The flow discharge is a random process and is expressed as the sum of mean discharge, Q m , and
fluctuating discharge, Q' :
Qt Q Q t (5.66)
The mean flow discharge, Q m , mean sediment discharge, Q sm , and the root-mean-square of the flow and
sediment discharges, Q rms and Q s-rms , respectively are also listed in the table, which are defined by
1/ 2
c
()
()
m
1/ 2
ª
T
º
ª
T
º
1
1
³
2
³
c
2
Q
(()
Q t
Q
)d
t
Q t
()d
t
(5.67)
«
»
«
»
rms
m
T
T
¬
¼
¬
¼
0
0
1/ 2
1/ 2
ª
T
º
ª
T
º
1
1
c
³
2
³
2
Q
(()
Q
t
Q
)d
t
Q
()d
t
t
(5.68)
«
»
«
»
s-rms
s
sm
s
T
T
¬
¼
¬
¼
0
0
where Q s is the sediment discharge, Q' is the fluctuating sediment discharge, and Q rms is the mean
sediment discharge, Q rms and Q s-rms are called the fluctuation intensities of the flow discharge and sediment
discharge, respectively. The fluctuation intensity is on the same order or even larger than the mean values,
demonstrating the flow is highly unsteady.
T able 5.6
Intensity of channel motion and fluctuation of flow discharge for the lower Yellow River near Zhengzhou
V scour
(10 6 m 3 )
V dep
10 6 m 3
V scour + V dep
(10 6 m 3 )
Q m
(m 3 /s)
Q rms
(m 3 /s)
Q sm
(t/s)
Q s-rms
(t/s)
R s
(m 2 /yr)
Time
1979.10
-1980.10
150.1
120.4
270.5
975.9
591.9
19.47
33.97
1907.8
-1981.10 219.4 193.9 413.3 1518.6 1703.4 41.87 70.59 2915.1
-1982.10 211.0 183.1 394.1 1330.5 1337.2 19.97 47.07 2779.7
-1983.10 227.2 239.1 466.3 1824.9 1506.7 26.7 39.30 3288.9
-1984.10 249.2 233.0 482.2 1402.2 1805.2 29.01 46.64 3401.0
-1985.10 256.6 194.0 450.6 1767.2 1501.2 24.9 47.60 3178.2
Note : The length of channel section of the measurements is 141.78 km, from the cross section at Guanzhuangyu to
the cross section at Dongbatou.
Analysis of the data reviewed that the intensity of channel motion is proportional to the square root of
Q rms :
s RmQ (5.69)
in which R s is in m 2 /yr and Q rms in m 3 /s, and m is a function of composition of bed sediment and constraint
factor for channel motion.
The motion of the river channel is reciprocating because the motion is caused by the fluctuation of the
flow discharge and the fluctuation is reciprocating. Some high frequency movement of the channel is not
reflected in the measured values in Table 5.6, therefore, the measured R s is smaller than the sediment-
removing capacity, but it may be assumed proportional to the sediment removing capacity, given in the
following formula:
rms
*
s
R R (5.70)
where k is a constant factor for a given river. Because the sediment-removing capacity results from the
fluctuation of discharge, the factor, k , can be determined by the analysis of the spectrum of the discharge
fluctuation. Using the daily-average discharge and performing an analysis of the spectrum of the
discharge fluctuation, Wang et al. (1997) concluded that if the intensity of channel motion is measured
with a measurement frequency of once a year the constant, k , is equal to 2 for the lower Yellow River.
s
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