Water Resources Management - Practices of Irrigation and On-farm Water Management - page 169

Import of Virtual Water
Where water is very scarce, the food or “virtual water” can be imported. In such situ-
ation, food imports may be invariably cheap below actual production costs. Gaining
access to secure “virtual water” in the global system can be achieved by developing
a diverse and strong economy. Alternatively, in oil-rich economies such access can
be secured through oil revenues.
Superabsorbents for Water Capture
Superabsorbents are compounds which absorb and hold water in a form readily
available to plants, slowly releasing this moisture in response to the change in
water concentration in the surrounding medium. Their main function is to reduce
moisture stress and transplant shock, thus creating optimum moisture conditions
for plant growth. The water-holding capacity of the various superabsorbents avail-
able ranges from 30 to 1,000 times their own weight. In landscape construction,
superabsorbents can be used as establishment aids for trees, shrubs, lawns and
instant application. Details regarding superabsorbents are described in Chapter 11 ,
Vo l um e 1 .
In water-short areas, there is usually no single solution for solving problems of
inadequate water supplies. Rather, a broad approach is needed, saving water, using
water more efficiently, and reusing water wherever possible. Only then can limited
water supplies in arid and semiarid regions be effectively managed.
5.3.2.3 Implementation of Supply Management Options
In general, large-scale groundwater development requires the construction of a
great number of wells and the use of a considerable amount of energy to extract
groundwater. Low-income developing countries face considerable difficulties in
implementing a groundwater development plan. In selecting the technologies to
be used, a number of factors have to be taken into account which go beyond
the physical merits of the technologies themselves, that is, human and financial
resources availability, compatibility with cultural habits, level of dependence on
foreign imports, etc.
Surface water schemes generally involve one or a small number of water storage
and/or diversion facilities. Such a centralized structure can be easily monitored by a
public, semipublic, or private organization. The availability of the resource is known
at all times with reasonable accuracy, and its handling is almost permanently under
control.
In groundwater development, two types of technologies may be considered for
access to and extraction of groundwater: intermediate and modern technologies.
Intermediate technologies :
- the open (dug) well, lined with concrete down to the water level and fitted with a
column of concrete rings below it