Flood Defense and Water/Sediment Management—With Particular Reference to The Yellow River - River Dynamics and Integrated River Management - page 384

Ex-minister of water resources, Madame Qian paid a field trip to the wandering lower Yellow River
and proposed to abandon the flood defense strategy with wide river valley, which has been applied as the
main flood defense strategy for the safety of lower Yellow River since the 1950s (Qian, 2006). The wide
river valley in the Henan reach of the lower Yellow River is too wide, more than 10-25 km. About 1.8
million people are now dwelling on the floodplain within the grand levees. The flood defense strategies
for the people on the floodplain are mainly perched refuge platform and flood refuge building. The
refuge platform and refuge building are effective for 20-years flood only and they are too expensive,
about $1200 and $2500 per person. Nowadays, sediment load and flood volume have been remarkably
reducing due to regulation of reservoirs. The 100-years flood has reduced from 33,000 m 3 /s to 15,700
m 3 /s and the 1,000-years flood has reduced from 45,000 m 3 /s to 22,600 m 3 /s. The wide river valley may
be changed to relatively narrow river valley. Madame Qian proposed to narrow the river valley from
10-25 km to 3-4 km. A new grand levee should be built on the left side of the river and the floodplain
between the new and old grand levees can be used for development of townships and industry. Modern
infrastructures, such as highways, railways and power facilities, may be constructed for economic
development. Figure 6.53 shows a picture of the narrow river valley and development of the floodplains.

Fig. 6.53 A picture of the narrow river valley and reclamation of the floodplains in the lower Yellow River

6.6.2 Scouring the Yellow River Channel with Seawater
Lin et al. (1998) proposed to divert sea water from the Bohai Sea and pump it into the Yellow River to
scour the river channel, because the river bed has been silting up quickly and there is less and less water
to be used for scouring bed sediment. Two schemes have been studied: 1) divert sea water from Guangli
Harbor and inject the sea water into the Yellow River near the Lijin Hydrological Station; 2) inject the
sea water at Xihekou, as shown in Fig. 6.21. In the first scheme a canal is suggested to connect the
Guangli Port and the Nanzhan Reservoir, which is now used as a flood detention basin. Sea water at
discharge of 500 m 3 /s will flow through the 48 km long canal and be pumped into the reservoir. It will
then be released with peak discharge of 5, 000 m 3 /s into the Yellow River (when the reservoir is fully
impounded). The capacity of the reservoir is 50 million m 3 . The reservoir can be draw down in 7 hours
and impounded again in 28 hours. The 115 km long river channel downstream of Lijin would be scoured
251 times per year, for each time the river channel is scoured 7 hours.
The effect of seawater scour was calculated with a simple numerical model (Lin et al., 1998). The bed
sediment was assumed to be 0.06 mm in diameter, and the sediment concentration in a flood is assumed
to be 25.5 kg/m 3 . The calculation demonstrated that the released seawater flood decreases as it moves
down the river. The peak discharge of 5, 000 m 3 /s at Lijin, reduces to 1,800 m 3 /s at Xi-he-kou (47 km
from Lijin) and to 1, 300 m 3 /s at the river mouth. Because the sea water flow carries no sediment, the
river channel is obviously scoured. The channel bed elevation at Lijin is scoured from 12 m to 6 m in the
first year before the flood season and resilted to 10 m after the flood season. More than 170 million tons
of bed sediment can be scoured and transported into the sea in five years.