Environmental Engineering Reference
In-Depth Information
Delivery ratio in wide and shallow channels —In wide and shallow channels, especially in the upper
part of the lower Yellow River, the width of flow increases with discharge but the velocity does not increase
with increasing discharge. Hyperconcentrated floods cause high sedimentation on the floodplain and the
sediment delivery ratio is small. Figure 5.34 shows the sediment delivery ratio in percent as a function of
the sediment concentration for the upper part of the lower Yellow River. For sediment concentrations
higher than 50 kg/m 3 , the delivery ratio is smaller than 100% and decreases with increasing sediment
concentration. For hyperconcentrated floods with concentrations higher than 200 kg/m 3 , the delivery
ratio is only 40-60% and serious sedimentation occurs in the reach.
Fig. 5.34 Sediment delivery ratio ( P ) in percent as a function of the sediment concentration ( S ) for wide and
shallow channels in the upper part of the lower Yellow River
Wang and Dittrich (1992) used the Rouse number Z to differentiate wash load and bed material load
for hyperconcentrated flow and low concentration flow. The group fall velocity of the sediment in the
Yellow River roughly follows the empirical formula given below, as shown in Fig. 5.35:
7
ZZ
(1
S
)
(5.55)
0
v
Fig. 5.35
The ratio of group fall velocity to the fall velocity of single particle,
ZZ in hyperconcen-trated flows
/
,
0
as a function of the volumetric sediment concentration, S v
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