efit to minimize the impact on the
environment and improved profitability of the producer.
All drainage works, small and large,
have certain requirements and the
following factors are important to
take into account:
Identify the purpose of what is
to be reached with the drainage
works,
Investigate all conditions and
obtain design information in the
field,
Make use of previous information and experience of a similar area and
Do a proper financial costing of
the project.
The basic steps of developing a subsurface drainage system are:
Investigation of the problem and
system planning,
Design of a drainage system,
Preparation of work drawings
and plans,
Compiling of specifications,
Installation of the sub-surface
system and
Maintenance of the system.
Typical layouts are shown in Figure
2 and depends on the specific circumstances and topography of the
area. Select a drainage pattern that
best fits the topography and the
groundwater conditions.
Figure 2: Typical sub-surface
layouts
Figure 3: Typical machine installation
The herringbone system (b) consists of parallel laterals that enter
the main at an angle, usually from
both sides. This system is used for
long, relatively narrow wet areas.
The parallel system (a) is similar to
the herringbone system except
that the laterals enter the main
from only one side. This system is
used on flat, regularly shaped
fields with uniform soil types. The
double-main system (c) is a modification of the parallel and herringbone systems. It is used where a
depression, which is frequently a
natural watercourse, divides the
field. A random system (d) is used
where the topography is undulating or rolling and contains isolated
wet areas.
Installation can take place either
manually (where trenches are dug
and pipes are laid by hand) or mechanically as shown in Figure 3.
Subsurface drainage is a high investment operation and thus a
greater return from agricultural
land is expected after installation
of subsurface drains. It is of ut-
most importance that this investment is safe-guarded by regular
maintenance.
Drainage systems are man-made
systems that are only implemented
when natural drainage is insufficient for a satisfactory form of agriculture and it is necessary to consider technical, economic and environmental issues when a project of
this nature is embarked on.
In many cases it is advisable to get
expertise advice to assist with subsurface drainage project and in this
regards the ARC-Institute for Agricultural Engineering has just completed a project that was initiated
and funded by the Water Research
Commission. The project report:
“Development of technical and financial norms and standards for
drainage of irrigated lands” will be
published in 2016 and provide
guidelines for planning and design
of sub-surface drainage approaches. An approach that will provide
effic ient drainage for improved soil
health and sustainability.