Applied geomorphology and arid regions
495
Figure 19.30. Channelled water from the San Juan River originally from the Andes. San Emiliano Dyke,
San Juan, Argentina. This water is put to several uses in this very dry area.
of Senegal (Fig. 19.33), which affect the availability of drinking and irrigation water. In
October 1968, salinity was low, coinciding with the rainy season. But in May 1984, the
whole river had a salt content higher than that of sea water (35%o). Close to its mouth, the
salinity of the fiver tripled this value (Farmer and Wigley, Unpub. data; in Mainguet,
1991).
As mentioned above, inadequate agricultural practices and over-irrigation cause
salinization, but they can also cause lixiviation. As stated by Mainguet (1991): "It is
absolutely vital that irrigation in arid or semi-arid ecosystems be considered a last resort,
especially for large projects."
Table 19.3. Approximate percentages of irrigated land affected by salinization in different countries
(Goudie, 1990a,b).
Algeria
10-15
India
27
Egypt
30-40
Iran
< 30
Senegal
10-15
Iraq
50
Sudan
< 20
Israel
13
USA
20-25
Jordan
16
Colombia
20
Pakistan
< 40
Peru
12
Sri Lanka
13
China
15
Syria
30-35
Cyprus
25
Australia
15 - 20