Flood Defense and Water/Sediment Management—With Particular Reference to The Yellow River - River Dynamics and Integrated River Management - page 333

greatly in the past 20 years. The long term (1950-1985) average sediment concentration was 40 kg/m 3
and the highest sediment concentration was recorded at 911 kg/m 3 . The ratio of the highest annual runoff
to the lowest is 3.4 and the ratio of the highest annual sediment load to the lowest is 10. More than 60%
of the water and 85% of the sediment are transported in the flood season from July to October. The
Yellow River, recognized as the cradle of Chinese civilization, is the most challenging river in the world.
It carries the heaviest sediment load and often experiences erosion and sedimentation that make the river
channel extremely unstable. The river watershed is mostly arid and semi-arid with a long term-average
annual runoff depth of only 77 mm and total annual runoff 58 billion m 3 . The water resource per capita in
the watershed is only about 500 m 3 , only one quarter of the average in China.
The sediment load of the lower Yellow River is mainly composed of silt; its mineral composition is
quartz, feldspar, calcite, and illite. The sediment is readily suspended and no distinct bed load motion can
be detected. Table 6.1 lists long term average values of water discharge and sediment load of the river;
they are obtained by averaging over 39 years (1950-1989) of recorded values. Table 6.2 lists the discharge
of floods of various recurrence periods for flood control design. The river deposits sediment at the river
mouth and on the north China plain and has created more than 250,000 km 2 of fertile land forming the
Pan Yellow River Delta with the apex at Zhengzhou.

T able 6.1 Average water and sediment load of the Yellow River in the period from 1950-1989

Hydrologic Station

Huayuankou (Zhengzhou) Lijin (Dongying)

43 billion m 3 30 billion m 3 Annual Runoff

Annual Sediment Load 1.6 billion tons 1.0 billion tons

40 kg/m 3 33 kg/m 3 Average Sediment concentration

Median diameter of suspended sediment 0.019 mm 0.019mm

6,860 m 3 /s 5,400 m 3 /s

Maximum day-average discharge

T able 6.2 Flood features of the lower Yellow River (Chen, 1999)

Peak discharge (m 3 /s) 5 days runoff (bm 3 ) 12 days runoff (bm 3 )

Hydrological
Station

Catchment
(km 2 )

100yrs 1000 yrs 100 yrs 1000 yrs 100yrs 1000 yrs

Huayuankou 730,036 29,200 42,100 7.13 9.84 12.5 16.4

Xiaolangdi 694,155 29,200 42,100 6.24 8.70 10.6 13.9

Sanmenxia 688,421 27,500 40,000 5.91 8.18 10.4 13.6

6.1.2 Flood Disasters in the History
Throughout the history of China, the Yellow River has been associated with floods and famine. The river
carries sediment produced by soil erosion from the Loess Plateau, which deposits on the channel bed
and in the estuary. Xu (1998) studied the sedimentation rate of the lower Yellow River applying map
comparison, historical literature studies, modern data analysis, and 14 C dating. He divided the past 13,000
years into 4 periods, as shown in Fig.6.2: 1) from 11,000BC to 3,000BC is a period of low sedimentation
with an average sedimentation rate of only 0.2 cm per year; 2) from 3,000BC to 600AD is a period with
accelerated sedimentation due to climate changes. The sedimentation rate increased to about 0.5 cm per
year in this period; 3) from 600AD to 1855 is a period with accelerated sedimentation caused by human
activities. The average sedimentation rate increased to 1-3 cm per year; 4) since 1855 human activities
have accelerated the sedimentation at an extremely high degree and the sedimentation rate has risen to
5-10 cm per year. The measured transverse riverbed profile at the Sunkou cross section in Fig. 6.3 shows
that the sedimentation of the lower Yellow River raised the riverbed and floodplain by about 5 m in the