Sediment Movement in Alluvial Rivers - River Dynamics and Integrated River Management - page 293

Fig. 5.29 Ratio of the concentration measured at 0.2 h from the water surface ( S 0.2 ) to the concentration measured at
0.8 h ( S 0.8 ), S 0.2 /S 0.8 , as a function of the average concentration, in which h is the flow depth (the numbers by the
points in the figure indicate the median diameter of the suspended sediment in mm)
Fig. 5.30 Manning's roughness coefficient n of hyperconcentrated floods and low concentration floods at the Xiaolangdi
Hydrological Station as a function of concentration
5.2.3.3 Wide and Shallow Channel and Narrow and Deep Channel
The river channel may be classified into three types according to the relation of the width/depth ratio, B/h,
with discharge. The channel is wide and shallow if B/h increases with increasing discharge; is narrow and
deep if B/h decreases with increasing discharge; and is transitional if B/h remains unchanged with increasing
discharge. Figure 5.31 shows the relation between the width/depth ratio and the flood discharge for the
lower Yellow River, the Weihe River, and the North Luohe River (Qi and Ru, 1995). The lower part of
the Yellow River (Luokou station), the lower Weihe River (Huayin station), and the North Luohe River
(Chaoyi station) have narrow and deep channels because the width/depth ratio decreases with increasing
discharge. On the contrary, the upper part of the lower Yellow River (upstream of the Aishan station) has
a wide and shallow channel (Huayuankou and Shangyuantou stations) and the width/depth ratio increases
with discharge.
Delivery ratio in narrow and deep channels —The delivery ratio is defined as the ratio of the amount
of sediment load transported by a flood through a reach of river to the amount of sediment load coming into
the reach from upstream. In narrow and deep channels, B/h decreases and the velocity increases with
increasing discharge. Consequently the sediment carrying capacity and sediment delivery ratio increase
with discharge. The sediment transportation in the narrow and deep channels exhibits the feature of “ high
incoming sediment load—high sediment delivery”. For the lower part of the lower Yellow River (below
the Aishan Station), the velocity may reach 2 m/s if the discharge is over 2,000 m 3 /s. The bed form