Abstract
The history of China is the tale of the Yellow
River, Huanghe. The basic characteristics of the river are the low
runoff of water and the high concentration of sediment. This
disequilibrium is the source of the problem, which causes sedimentation
and a rising bed of the lower Huanghe, gradually making it a hanging
river, and causing frequent floods, avulsions and diversions. The
water mainly comes from above Lanzhou, while the sediment originates
from the soil erosion in the Loess Plateau. This can be illustrated as a
gigantic sandglass, with the upper part collecting the water and silt
into the river and the lower bulb delivering these to the vast plain.
The coarse particles are clearly identified as the source of
sedimentation. Major source areas of coarse sediment coincide well with
those where the erosion is most intensive. In any year sediment
production is controlled by a few thunderstorms in summer, especially
within a 15-20 minute period. The reasons for erosion are simple; over
the centuries forests have been cut down, vegetation destroyed by
overgrazing, the hillsides overworked by the hoe and not terraced to
slow down the runoff of summer rains.
The history of harnessing the Huanghe can be
traced back to emperor Yu, who was the first person to succeed in taming
the river. From the
Zhangguo period man began to control the river by dikes. Since the Han
dynasty the channel of the lower reaches of Huanghe has been broken by
natural causes many times and on large scales. This is an inevitable
result of the development of the mature stage of the river. The
suspended river is the end result of development and it cannot be
retrieved by manpower. Ancient Chinese scientists were concerned mainly
with the problems in the river’s lower reaches; river dredging,
floodwater diversion and retention, establishment of a levée system and
increasing the silt-carrying capacity. Today there is an overall plan
for the upper, middle and lower reaches. In the Loess Plateau water and
soil conservation works are the most efficient methods. In the lower
reaches there are two ways to go in flood prevention, because the dikes
cannot be heightened indefinitely; 1) to build a new channel, 2) to
maintain the status quo. The latter includes improved efforts to increase
the capacity of flood and sediment discharges. The long-term perspective
is within the reach of 50 to 100 years.
The problems of flooding are affected by many
factors. Therefore a single measure may not satisfy the overall solution
of flood control. To solve the problems of sedimentation of the Huanghe,
a policy involving a variety of measures for comprehensive control needs
to be adopted.
Keywords: Huanghe, erosion, flood control