Sediment Movement in Alluvial Rivers - River Dynamics and Integrated River Management - page 311

the channel. The river flow exhibited high sediment-removing capacity and low sediment-carrying
capacity.
Fig. 5.48 Wandering of the Jamura River channel near Bahadurabad. (a) Contour lines of different water depths in
September 1993; (b) Contour lines of different water depths in November 1993 (Barua et al., 1995)
The lower Yellow River is a wandering river with bed material mainly composed of silt and fine sand
of median diameter about 0.02 mm. The sediment is very erodible. Bank erosion occurs at one side,
while sediment deposition occurs at the other side of the channel. Although sedimentation dominates the
long-term fluvial process of the river, short-term river adjustment is variable in time and space. The
Yellow River flows out of the mountains at Xiaolangdi and develops a fluvial stream on the north China
plain, which is indeed created by the river sedimentation. The stream, with a normal flowing width of
only about 500 m, creeps within a 5-25 km wide river valley, defined by the grand levees.
The wandering channel was observed at many hydrological stations and measurements of the riverbed
were performed at numerous cross sections. Table 5.5 lists the river motion distances at these sections
and hydrologic stations. Table 5.5 illustrates that the maximum distance of the river motion is over 8 km
and the motion distance in one year is over 5.6 km. The local farmers told the authors that the speed of
the river motion could be as high as 100 m/day. A farmer watched his bicycle on the bank falling into the
flowing water and had no time to rescue it when the flow assaulted the bank.
To stabilize the river channel, the local people have built many spur dikes along the main stream,
like the Jiabu spur dyke built in 1973. Nevertheless, many of the spur dikes do not work well because the
river channel moved far away from them after the spur dikes were completed. Figure 5.49(a) shows the
spur dike at Kaiyi, a short distance upstream from Zhengzhou (Huayuankou). The spur dike controlled
the river channel for a short period of time, then the channel migrated away from the spur dike, as shown
in Fig. 5.49(b).
A wandering river is difficult to train. The capacity for channel motion is due to the high concentration
of sediment and the unsteady discharge and unsteady sediment-carrying capacity. With regulation of the
discharge and trapping of sediment by reservoirs, especially the recently completed Xiaolangdi Reservoir,
both the unsteadiness and the sediment load released into the lower Yellow River have reduced. Therefore,
the speed of channel migration will decrease.