Basic Concepts and Management Issues of Rivers - River Dynamics and Integrated River Management - page 34

Fig. 1.28 People escaping from the flooded floodplain at Changyuan, which is in Henan Province near Zhengzhou
during the 1996 flood period
In 1998 a rare flood occurred on the Yangtze River, which resulted in serious flood damages and
affected 8 million people. Heavy rainfalls occurred in the area in the summer of 1998 in the wake of the
strongest El Nino phenomenon of the century, which reached its maximum at the end of 1997 and ended
in May 1998. Meteorologists have hypothesized that this phenomenon increased the snow accumulation
in Europe and on the Qinghai-Tibet Plateau. Because more snow accumulated, the monsoon was delayed
and the major rain belt was shifted to the South, and more rain fell in the Yangtze River Valley.
The recurrence period of the 1998 flood is only 8 years in terms of the crest flood discharge and the
recurrence period is about 100 years in terms of flood volume (Ministry of Water Resources, 1999). During
the flood, one levee breach occurred at Jiujiang City on the Yangtze River and it was closed in several days.
The cities and main railways and highways were not affected by the flood. The flood caused 1,075 polder
levee breaches, inundated 321,000 ha of land. The death toll was 2,292, most of which were the victims
of flash floods and debris flows in the mountains.
The flood disasters in recent years exhibit new features different from the traditional flood disasters. In
summary, flood disasters in China are more frequent than in earlier times because increasing population
pressure and economic development are changing the river regime, and the flood control system has not
matched the change (Cheng, 2002). The disastrous flood on the Yangtze River in 1998 is a result of
abnormal heavy rainfall, but the extremely high flood stage is due to less flood diversion, reduced
regulation capacity of riparian lakes, and channel sedimentation. The Yangtze River also experienced
higher stages at lower flows in the 1998 flood compared with the 1954 flood. New river management and
flood control strategies are needed to meet the challenge of flooding.
1.2.3 Soil Erosion
Environmental health encompasses the maintenance and quality of the natural resources: soil, water, air,
and biota. According to preliminary statistics compiled for the world, the annual erosion of surface soil
from river basins amounts to 60 billion tons, of which 17 billion tons are discharged into the oceans. In
the process, as much as 5 to 7 million ha of farms are annually ruined. Moreover, aeolian erosion of bare
lands has intensified desertification after depriving the ground of good top soil. Eroded soil contains
nitrogen, phosphorous, and other nutrients that deposit in lakes and reservoirs contaminating the waters
resulting in eutrophication and other biological as well as chemical processes.
China is a country suffering severe erosion, with 1.82 million km 2 subject to water erosion, 1.88 million
km 2 subject to aeolian erosion, and 1.25 million km 2 subject to glacial erosion. In other words, more than