Geoscience Reference
In-Depth Information
probably saved many lives, but the banks have failed in numerous places over the years,
still causing inundation on a catastrophic scale.
One of these levée failures, in 1938, was deliberate. During the war against the Japanese,
the Chinese Nationalist government ordered its army to dynamite the levée at Huayuankou
in an attempt to stop the advance of Japanese forces with an intentional flood. Although
several thousand Japanese troops were drowned, the flood only delayed the enemy ad-
vance. The brunt of the disaster was borne by the local Chinese population. Eleven cities
and more than 4,000 villages were inundated. In total, about 12 million people were affec-
ted, nearly 900,000 of them drowning. It was nine years before engineers repaired the levée
at Huayuankou and the river resumed its course to the Bohai Sea.
Centuries of levée construction have had other effects. Most rivers in their lower courses
deposit mud and silt, and the Yellow is no exception. However, because the river floods
only rarely in its lower course, thanks to the levées, most of the material is deposited on the
bed of the channel itself. Hence, the river channel has slowly gained height over the centur-
ies, and the levées have had to be raised accordingly. Today, the bed of the lower reaches is
on average some 5 metres higher than the land outside its dykes. At Kaifeng, the river bed
is 13 metres higher than street level. The residents of Xinxiang go about their business no
less than 20 metres below the adjacent Yellow River. The phenomenon is often referred to
as a 'hanging river'.
Since the 1960s, a number of large dams and reservoirs have been built in the upper and
middle reaches of the Yellow River. They are designed both to help control floods and
to supply the 100 million people who rely on the river for their fresh water. The rising
demands on the Yellow River's water have created a scarcity, to the extent that in the
early 1990s the river failed to reach the sea on certain days. By 1997, there were 226 'no-
flow' days, the dry point starting 700 kilometres inland on some occasions. Since then, the
Chinese government has ensured for political reasons that the river always reaches the sea,
albeit in small volumes. But the river now certainly delivers much less than a billion tonnes
of sediment a year to the North Pacific. With so little water actually flowing in the hanging
part of the river, the chances of a flood have decreased, but the possibility remains that a
major flood further upstream will be too great for the dams to contain and the levées on the
lower Yellow will once again be breached, with terrible consequences.
Dams
