S
ub-surface drainage of agricultural lands is an instrument for production
growth, a safeguard for sustainable investment in irrigation and
a tool for conservation of land resources. There are however pressing
needs for more investment in landdrainage systems to maintain current
production levels in existing agricultural systems around the world and
to drain degraded and abandoned
agricultural lands.
Artificial drainage in agriculture is a
practice to improve the natural drainage conditions and has been practiced for many years in the world. In
South Africa drainage was introduced in the late fifties and early sixties and various approaches and
techniques have been used and are
still been used to drain agricultural
fields in South Africa.
In South Africa an area of 16 000
000 ha is been cultivated and 1 600
000 ha registered for irrigation. It is
estimated that 240 000 ha is affected
by rising water tables and salinisation
and problems appear to be expanding. There are many causes of drainage problems in South Africa. Some
typical causes of drainage problems
are:
inefficient and badly managed
irrigation systems, especially
where there are very shallow soils
and insufficient natural drainage.
Salts start then to accumulate and
the end result is that the land has
Felix Reinders
ARC-Institute for Agricultural Engineering
to be withdrawn from production,
leaking earthen dams and irrigation furrows,
in some areas terraces are designed and established in order
to obtain the right slopes for
flood irrigation but, unfortunately, sooner or later drainage
problems start to occur at the
bottom of these terraces, and
where natural waterways are
being cultivated, wet conditions
are expected and therefore
drainage problems. See figure 1.
Sub-surface drainage systems have
proved to be an essential method
to restore the productivity of agricultural lands, especially in arid and
semi-arid zones. These agricultural
sub-surface drainage systems can
be used for:
Reclamation of new land with a
groundwater table and/or soil
salinity that is too high;
Controlling groundwater levels
at desired depths and soil salinity at desired levels;
Restoring the productivity of
water logged and/or salinised
lands to their potential levels.
The need for subsurface drainage in
irrigated lands cannot be overemphasized as it has proved to be a
sustainable and proven solution to
both water logging and salinity
problems. By correcting the water
table status and the salinization
together with the installation of a
proper erosion control system, it
can improve soil health and crop
production and it will have the ben-
Figure 1: Example of water table close to the ground surface.