Environmental Engineering Reference
In-Depth Information
All these activities can be viable only if sufficient water is available to meet the
increasing domestic, industrial and agricultural demand. These demands vary enormously
between the different activities, from the low demands for drinking (potable) water,
through the medium demands of industry, to the very high demands of agricultural
irrigation. Table 26.1 shows the water requirements for different purposes; as a rough
rule of thumb, it is said that an inhabitant of a Mediterranean area consumes ten times
BADLANDS
human impact
The visitor to the Mediterranean never forgets the spectacular 'badland' scenery which,
though highly localized, leaves an unforgettable impression; this is the landscape of the
'spaghetti' westerns, and the glossy photos of 'desertified' areas in colour magazines.
Badlands are named after the
mauvaises terres
seen by eighteenth-century French
travellers in North America. In the Mediterranean region, badlands are found in Spain
(Guadix, Tabernas, Murcia, the Ebro valley), in Italy (Tuscany, Basilicata), Greece
(Grevena, Corinth, Serres) and in Asia Minor (the Maeander valley in south-west
Turkey). Badlands also occur in the Mediterranean parts of Australia and California. The
Mediterranean-type climate favours their formation, though they are not restricted to the
Mediterranean-type environment, and are found in semi-arid regions (North Africa,
Australia), under continental climates (the Great Plains of the United States, the Dinosaur
and Big Muddy Badlands of Alberta, Canada) and even in warm-temperate and tropical
locations (Nigeria; Georgia and Alabama in the United States). The dominant
geomorphic process in these highly eroded and dissected landscapes is gullying; a
gully
is a large, well defined channel, typically V-shaped, whereas a
rill
is clearly defined but
smaller and impermanent, often being destroyed by flaking of the surface by drying, by
frost or by ploughing. Rills are more common in ploughed fields and road cuts, but
gullies can form on both cultivated and uncultivated land. A badland area typically has an
intensive network of channels and valleys with steep and bare slopes, a high drainage
density of over 50 km km
−2
and a high relative relief of up to 30 m. Overland flow carries
out the bulk of the erosion, and this explains why most badlands are restricted to soft
rocks such as marls and clays of Tertiary and Quaternary age with very low infiltration
rates. Often these materials have high sodium contents and
