Geoscience Reference
In-Depth Information
The most destructive flooding occurred during this
period, in 1332 AD, with seven million people
drowning and over ten million people dying from
subsequent famine and disease. By 1851, the Hwang
Ho had aggraded its bed in the south to such an extent
that it threatened to engulf the town of Kaifeng.
Measured rates of aggradation exceeded 2 m yr -1 , and
dykes more than 7 m high were built to contain its
flow. Between 1851 and 1853, the Hwang Ho broke
out northward and took on its present course. In
1887, a temporary breach saw the river move the
furthest south it has ever been. It temporarily linked
up with the Chang (Yangtze) River and, for a brief
time, both rivers flowed out to sea through the same
channel. The 1887 flood breached 22 m high embank-
ments and flooded 22 000 km 2 of land to depths of
8 m. Over a million people lost their lives. Not only
was the death toll severe, but the river also buried
flooded land in meters of silt. Farmers relying upon
the river in the northern part of the delta suddenly
found themselves without irrigation water and facing
starvation. Twentieth century floods have been com-
paratively less severe; however 200 000 and 300 000
people were killed in the floods of 1911 and 1931,
respectively.
The natural tendency of the Hwang Ho to shift
course has been greatly exacerbated during wartime.
In 1938, General Chiang Kai-shek, in an attempt to
prevent advancing Japanese armies taking the city of
Chengchow, ordered the levee dikes to be dyna-
mited. The diversion failed to stop the Japanese
advance, but the ensuing floods killed a million
unsuspecting Chinese, and possibly caused the death
of 11 million people through ensuing famines and
disease. It was not until 1947 that extensive engineer-
ing works forced the Hwang Ho permanently back
into its prewar channel. Today, the Hwang Ho is sta-
bilized for much of its length, and is kept to the north
of the Shandong Peninsula. Because the river trans-
ports such large quantities of silt, its bed is continuing
to aggrade and now sits 20 meters above its flood-
plain, the latter protected by an inner and outer set of
dikes spaced 10 km apart. The Chinese government
has embarked on a program of dam and silt basin
construction to minimize the flooding effects of the
Hwang Ho; however, the river is still not controlled,
and will probably breach its dikes in the future during
a large flood.
CONCLUDING COMMENTS
(Tropeano et al., 2000; Kunkel, 2003; Sheffer et al., 2003)
The wide scale nature of recent flood events is not
unique in time. Rather it represents the continuation
of a longstanding global hazard that has taken
millions of lives. For example, in Canada, there has
been no change in the frequency and intensity of
extreme precipitation events during the twentieth
century. Similarly, in the United States (where there
has been an increase of 20-40 per cent in extreme
precipitation over the long-term average of the last
two decades of the twentieth century), flooding today
is just as prominent as it was at the end of the nine-
teenth century. These changes are due to warmer sea
surface temperatures in the tropical Pacific Ocean
causing subsequent flooding in the United States.
Likewise, what might appear to be the largest floods
on record can be shown to be part of a continuum.
For example, on 8-9 September 2002, the Gardon
River in southern France reached a flood crest 14 m
above normal following 680 mm of rain over
20 hours. However, this flood did not reach a cave
lying 3 m higher that contained evidence of five
separate flood events dating between 1400 and 1800.
Similarly, on 14-15 October 2000, major flooding
accompanied by landslides affected the Italian Alps.
The floods were triggered by 400-600 mm of rain
that fell within two days. However, many of the land-
slides represented the partial reactivation of much
larger historical slides. In Australia, at least eleven
comparable floods of similar magnitude have
occurred at 20-40 year intervals since 1810. There is
thus substantial evidence that flooding is ubiquitous.
Recent floods across the globe have not been
abnormal, but reflect the occurrence of events as
part of an ongoing continuum.
REFERENCES AND FURTHER
READING
Australian Bureau of Meteorology, Australia 1984. The Estimation
of Probable Maximum Precipitation in Australia for Short
Durations and Small Areas. Australian Bureau of Meteorology
Bulletin No. 51.
Australian Bureau of Meteorology, Australia 1985. A Report on the
Flash Floods in the Sydney Metropolitan Area Over the Period
 
 
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