Geography Reference
In-Depth Information
Syr Dar'ya. So great has been the expansion of
irrigated cotton and rice that near total diversion
of the waters of the two rivers has occurred. Most
of the water that is used for irrigation is lost as
evaporation.
Because the Aral Sea is a basin of inland
drainage it has been particularly sensitive to the
depletion of its water supplies. The lake level has
fallen greatly and at present the water area is less
than half of what it was in 1960. As the lake level
has declined and the water become more saline,
large areas of former lake bed have been exposed.
These lacustrinal sediments contain high salt
levels and when eroded by the wind have been
deposited on adjacent irrigated land causing
severe salt pollution. The irrigation projects
themselves have also created ecological problems.
Many schemes were provided with inadequate
drainage systems, so salinisation of the soil has
become widespread. A wide range of chemicals
and fertilisers were utilised in the production of
the cotton and rice, and these have now polluted
the surface and groundwater resources. The
overall result is that the natural ecosystem has
changed so significantly that it is not too extreme
to describe it as an ecological disaster (Micklin
1988). Various plans have been put forward to
obtain extra water supplies for the basin,
including the diversion of water from the large
rivers flowing into the Arctic Ocean. However,
the huge cost of such projects makes it unlikely
that they will ever come to fruition. Equally, it
would appear unrealistic to reduce irrigation
water volumes significantly, as in excess of 40
million people are today dependent on the
agricultural production of the basin (Kirmani
and Le Moigne 1997).
In recent years, since the advent of the pumped
well, many large aquifer systems throughout the
world have been overdeveloped or mined to
produce prosperous irrigated regions. A striking
example is the Ogallala aquifer underlying the
High Plains of Texas (Green 1973). The pace of
development of irrigation in the region was quite
remarkable, and from 1945 to 1970 the irrigated
area grew from less than 0.2 million hectares to
almost 2 million hectares (Figure 12.5) (Beaumont
1985). After a number of years of high levels of
extraction the water table began to fall, in some
areas by over a metre a year, and the costs of
obtaining the water grew as a result. The situation
was made even worse by rapidly increasing energy
prices from the late 1960s onwards. Inevitably the
profitability of irrigated agriculture declined, and
by 1978 the irrigated area had peaked. Thereafter
it began to decline.
The response of the farmers to the fall in the
water table was to try to get the state to provide
extra water by importing it from outside the state.
This idea was first put forward in the Texas Water
Plan of 1968, but at that time and on later
occasions the voters of the state voted down the
proposition for providing the funds necessary to
build it. As a result, the farmers of the High Plains
were forced to resort to new strategies to cope
with declining water volumes from their wells and
increased pumping costs. One of these was to
select crops that were better suited to the dry
conditions of the High Plains. Another was to
introduce moisture conservation techniques so
that the natural precipitation of the region could
be maximised. The overall result was that much
more use was made of the natural precipitation,
and irrigation was used only in a supplemental
form.
Despite all the changes that have taken place,
the irrigated area on the High Plains has
continued to contract quite markedly. The basic
problem has been that groundwater mining of the
Ogallala aquifer is not a sustainable activity that
can continue indefinitely. The farmers have chosen
to exploit the water as a short-term resource, in
much the same manner as oil might be pumped
out of the ground. All of them would now accept
that the water is a finite resource, and once it has
been pumped out it will not be replaced in the
short term. It is interesting to note, though, that
the water from the Ogallala has been able to
produce a prosperous agricultural system on the
High Plains that has already lasted fifty years and
with careful stewardship of the remaining
resources might well continue for a number of
decades.
