Geography Reference
In-Depth Information
Schilfgaarde 1990). There is evidence to suggest
that under ideal environmental conditions
irrigation can be practised for long periods of
time with few problems developing. An example
that is often quoted is the Nile valley, where
continuous cultivation at the same point does
seem to have occurred for at least hundreds, if
not thousands of years. However, the floodplain
of the Nile is blessed with ideal under-drainage
conditions in the form of gravel layers, which
have minimised the build-up of saline soil
conditions. Elsewhere, however, there is evidence
that under certain environmental conditions
long-term irrigation can lead to a lowering of
crop yields as water tables rise to such an extent
that economically viable crop production is not
possible. This might well have been the case in
the Tigris-Euphrates valley (Adams 1978;
Jacobsen and Adams 1958).
It is very difficult to determine the exact
nature of modern irrigation projects as few have
been in existence for more than 100 years.
However, many schemes do appear to begin
successfully but then experience growing
difficulties after a number of years as soil
conditions deteriorate (Gardner andYoung 1988;
Tanji 1990). Such declines in productivity may
show themselves after a few years on some
projects but may take many decades on others.
Overall, it is difficult to state categorically just
how irrigation should be regarded. After all, even
traditional dry farming is capable of producing
considerable environmental degradation when
practised over long periods, as the Mediterranean
region clearly demonstrates. Perhaps too often in
the past it has been assumed that irrigated
agriculture does not have significant
environmental costs, as it appears to be such a
controlled and artificial environment. In the
future, it might be expedient to think of
irrigation as a mechanism for causing potentially
serious environmental stress when it is practised
without careful consideration of all the possible
consequences (Umali 1993).
As the twenty-first century approaches,
another basic question that has to be posed is
whether large volumes of water can continue to
be used for what is essentially low-value irrigated
food and fibre production when demands for
water for more economically valuable uses are
growing rapidly (Beaumont 1994; 1997). The
issue, therefore, is about how water can be
utilised for the maximum benefit of society. The
likely answer to the question will depend on the
level of development of the society being
considered. For example, in traditional societies
such as the Palestinians on the occupied West
Bank, the use of water in irrigated agriculture
seems to be one of the few ways in which wealth
for the whole community can be generated. In
contrast, in the adjacent country of Israel, which
now has a much more mature urban/industrial
society, the continued use of water for irrigation
appears a very wasteful use of available resources.
For Israel, which is already suffering from severe
water shortages, the water problem in future can
only be alleviated by the reallocation of water
from irrigated crop production to more valuable
urban/industrial uses.
In the United States, the relationships between
irrigated agriculture and the urban/industrial
uses of water have always been complex.
Surprisingly, competition between the two water
uses began as early as the latter years of the
nineteenth century, when the irrigation boom in
the USA was just beginning. One of the best
examples is to be found in terms of the water
supply of Los Angeles (Hoffman 1981; Walton
1992). What happened here was that the city
fathers realised at the end of the nineteenth
century that indigenous water resources were
very limited and that something had to be done
to ensure that future water resources were
available for the city. Their solution to the
problem was to buy up agricultural water rights
in the Owens Valley in a period of little over a
decade. The means employed at times seem to
have been close to being illegal, but the net result
was that the city of Los Angeles did obtain a large
volume of water to supply its future needs. As far
as the Owens valley was concerned, what had
once been a fertile and green valley floor
supported by irrigation was turned into a region
of brown, semi-arid scrubland.
