Flood Defense and Water/Sediment Management—With Particular Reference to The Yellow River - River Dynamics and Integrated River Management - page 340

reduction in slope results in sedimentation and continuous silting up of the riverbed. The width of the
river valley is 5-20 km controlled by Grand Levees in the Henan Province reach (about 200 km). Figure 6.8
shows the river and the Grand Levee and spur dykes controlling the flow. The channel is about 500 m
wide and in most time the flow is kept in the channel. If a flood occurs the water is allowed to flow over
the floodplain for reduction of flood losses in lower reaches. The wide river provides water detention
capacity and space for sediment deposition. The wide river in the Henan reaches detained 2.4 billion m 3
of water during the 1958 flood and greatly reduced the flood discharge to the lower reaches (Wang, 1989).
The capacity of the channel in the Henan reaches is 30,000 m 3 /s. Nevertheless, the wide floodplain is
rarely flooded and about 1.8 million people reclaimed the land and live in villages and towns within the
Grand Levees nowadays.
To stabilize the channel and protect the villages and towns within the levees, numerous spur dykes
have been constructed. The spur dykes were constructed at the bends of the channel to control the flow
direction. Nevertheless, not all the spur dykes work well for channel stabilization. The river channel is
very dynamic and often moves far away from the dykes, which makes the dykes abandoned. Statistically,
about half of the spur dykes are effective for stabilization of the channel.

Fig. 6.8 Wide river valley defined by the Grand Levees in the reach in Henan Province

6.2.2 Narrow Channel
The most downstream reach of a length about 600 km of the Yellow River across the Shandong Province
has a width of only 0.4-5 km. The narrow river favors a stable channel and high flow velocity and
maintains high sediment carrying capacity, which is in accordance of the theory of narrowing the channel
and enhancing the sediment carrying capacity developed by Pan Jixun. On the other hand, the capacity of
the channel is limited, and can only accommodate floods of discharge less than 10,000 m 3 /s. The Aishan
Hydrological Station is the control point between the wide valley reach in Henan Province and the
narrow channel reach in Shandong Province. The Aishan cross section has a width of only 275 m. The
location of the Aishan station is shown in Fig. 6.1. The narrow section controls the flow into the
Shandong Reach no more than 10,000 m 3 /s. Therefore, it is named by the hydraulic engineers as “Aishan
Lock”. From Aishan to the river mouth the river is narrow. Figure 6.9 shows the Lijin cross section,
which is the most downstream hydrological station of the river (the location of the Lijin station is also