Geoscience Reference
In-Depth Information
23
Historic floods and droughts
I did not know thee in the wilderness, in the land of great drought.
Hosea 13.5
The effort to control the health of land has not been very successful.
It is now generally understood that when soil loses fertility, or
washes away faster than it forms, and when water systems exhibit
abnormal floods and shortages, the land is sick.
Aldo Leopold (1887-1948)
A Sand County Almanac
(1949)
23.1 Introduction
Anyone who has travelled widely and frequently in deserts may at some stage have
experienced the full might and majesty of a desert flood. These rare events, once seen,
are never forgotten. I retain vivid memories of the sudden and prolonged downpour
on 5 August 1999 and of the ensuing torrential flow from the nearby mountains across
the wide boulder-strewn valley floor we were crossing, which brought to an end the
three-year drought in the Right Banner area of the Alashan Plateau of Inner Mongolia
in arid northern China. The widespread floods in the northern uplands of Tunisia and
Algeria, which culminated on New Year's Eve 1969, were associated with heavy rain
as far south as the Saharan oases of Biskra and Toggourt - a boon to the local people
despite the temporary discomfort. The floods of January 2007 in the arid Flinders
Ranges of South Australia saw huge River Red Gums (
Eucalyptus camaldulensis
)
transported westwards across the mountain piedmont to be dumped in great tangles
on the surface of the flood-plain. Since the ephemeral stream channels were already
incised more than ten metres into these plains, the flow velocity across the flood-plain
must have been substantial. Considerable loss of life may ensue from these sudden
floods. In early 1941, most of the local inhabitants of Kufra Oasis in the south-east
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