Geoscience Reference
In-Depth Information
disaster relief in Australia, and led to significant
changes in the response to disasters by both private
relief organizations and federal government agencies.
Eleven months later these revisions were tested to the
utmost when Cyclone Tracy destroyed the city of
Darwin.
The floods of 1990 hit a region from central
Queensland in the north to Gippsland in the south. On
18 April 1990, a strong upper-level low developed over
the interior as a high-pressure cell stalled over the east
of the continent. Up to 350 mm fell initially over
central Queensland, triggering major floods of every
creek, stream, and river. On 21 April, floodwaters
converged suddenly on the Warrego River and swept
through Charleville. Residents had to be rescued from
rooftops by helicopter. Over the next few days both
the rains and the floods slowly tracked southward,
inundating one riverside town after the other. At
Nyngan on the Bogan River, residents decided to 'fight
it out' and began sandbagging the levees around the
town. Television crews moved in to report nightly on
their heroic but futile efforts. Over 200 000 sandbags
were laid in four days.
In Australia, a national emergency can be declared
only if someone reports it to the state government who
then requests federal assistance. In anticipation of
that call, Emergency Management Australia called in
500 troops who stationed themselves in the nearest
town waiting to help. In the confusion and excitement
of the flood, no one called for help. Finally, as the flood
broke through the levee, television crews filmed
people flinging themselves into the gaps in a last-ditch
effort to stay the inevitable. Within an hour the town
was flooded and helicopters evacuated the 2500
residents to Dubbo where the army had been waiting.
The disaster continued southward as rivers sequen-
tially broke previous flood heights by a metre or more.
The low, which was blocked eastward by the Great
Dividing Range, finally exited the continent through
Gippsland, Victoria. Here, up to 350 mm of rain fell
within 48 hours, causing major floods on all rivers
flowing from the Snowy Mountains. In the space of
four days, this single low-pressure cell had flooded a
landmass the size of western Europe in one of the
worst mass floods in Australian history.
The floods of 1998 illustrate the extent of flooding
that can occur in Australia during a La Niña event.
Five flood events occurred from Katherine in the north
to the Gippsland in the south. The interior of the
Australian continent receives most of its rainfall from
tropical cyclones that can move inland long distances
without the impediment of mountains. In January
1998, tropical Cyclone Les, which had developed
over the Gulf of Carpentaria, moved westward and
weakened into a rain depression. However, it stalled
over Katherine in the Northern Territory and between
25 and 27 January, it dropped 400-500 mm of rain on
the Katherine, Roper, and Daly River catchments.
Floodwaters on the Katherine River rose to a record
level 20 metres above normal. This was sufficient to
send two metres of muddy water through the town of
Katherine. The town's 2000 residents left evacuation
too late, fearing looters or believing that the flood
threat was highly exaggerated. Over 1100 people had
to be treated for injuries sustained while coping with
the disaster.
The shift to a La Niña event is often marked by an
increase in the frequency and intensity of east-coast
lows. One such low caused heavy rains that flooded
Gippsland on 23-24 June, while another caused
flooding at Bathurst, west of Sydney, on 7-8 August.
Finally, on 17 August, a small low developed along the
500 m escarpment backing Wollongong on the New
South Wales coast. In the early evening, extreme
rainfalls caused flash flooding that destroyed 700 cars
and caused over $A125 million damage. In all areas,
the flooding was not unique. Historic and palaeoflood
evidence indicates that floods with up to three times
the volume of the 1998 floods have occurred in all
three regions in the last 7000 years. In Wollongong, the
1998 floods were simply part of a spectrum consisting
of 80 or more floods that have occurred since the early
1800s. Much of the perception of increased flooding in
Australia reflects media hype, increased urban growth
and a stubborn resistance to learn from the lessons of
previous floods.
Floo
ding in China
(Bolt et al., 1975; Czaya, 1981; Milne, 1986)
Flooding in China is mainly related to the vagaries of
the Hwang Ho (Yellow) River channel. The Hwang Ho
River - China's River of Sorrow - drains 1 250 000 km
2
and flows over a distance of 4200 km (Figure 6.14).
Throughout much of its upper course, it erodes yellow
loess
, and for 800 km of its lower length, the Hwang
Ho flows without any tributaries on a raised bed of silt.
Much of this material has entered the river because of
poor land-use practices in the upper drainage basin in
