Centre pivot evaluations
Computerised irrigation design
An Israeli computerised irrigation
design package was introduced in
SA in 1983 and the International
Commission on Irrigation and
Drainage (ICID) predicted in 1985
that an integrated computer process will be the norm for the future
and indeed since then a number of
computer-aided design routines
were developed and reported on. In
1987 MBB Consulting agricultural
engineers completed a WRC supported project titled “The development of procedures for design and
evaluation
of
irrigation
systems” (MBB Inc., 1987). Irrigation
design principles and procedures
were studied in depth and evaluated critically. Different design algorithms were developed that were
based on the well-known polyplot
principles. The research eventually
resulted in the development of the
IDES irrigation design and evaluation programme which was the
front runner for the popular design
programme Modelmaker that was
only introduced towards the end of
the century. Today an excellent
computer programme is available
for modern day design of efficient
irrigation systems.
Containing losses during centre
pivot irrigation
During the period 1970-1982 the
efficiency of centre pivots was estimated at 80%. A research project
was supported by the WRC to investigate, identify and quantify the
spray losses between the emitters
on a centre pivot and the plant canopy. Apart from technical measurements, meteorological and other
factors influencing irrigation losses
were identified. It was found that
the average losses rarely exceed
10% of the pumped water if the
emitter package is properly designed and wind speeds is less than
6 m/s. From the results obtained
with single nozzles it was clear that
droplet size has an important effect
on spray losses. This research provided valuable guidelines in terms
of emitter selection, application
depth and management of centre
pivots.
Infiltrometer to size centre pivots
With the introduction of Centre
pivots in the late seventies early
eighties it brought about a new
design approach as far as the application rate is concerned. With a
centre pivot where the system rotates about a pivot point, the outside tower travels a longer distance
and thus covers a larger area than
the inside tower. Thus the application rate increases progressively
towards the outside sprinklers to
obtain the required application
along the whole length. If the appli-
cation rate exceeds the infiltration
rate of the soil runoff occurs which
lead to water losses. ARC-IAE researched and introduced an infiltrometer to give the designer a
technique and aid to determine the
soils infiltration rate to adapt the
pivot to the soil. In 1986 it received
international recognition and is still
used to size centre pivots.
Irrigation design manual
ARC-IAE’s agricultural engineers
researched and developed in 1993
manuals (since then it has been updated) to assist decision makers and
designers to utilise the right approaches and equipment to adapt
irrigation systems to southern African conditions. In this regard, the
Irrigation Design Manual, the Irrigation Operational Manual and the
Irrigation Evaluation manual covering both the small-scale and the
commercial farming sectors are in
huge demand and the manual
serves as textbooks at universities
and universities of technologies, as
well as reference to all technologists in the field. Both these publications are regarded as the references in its field in South Africa today.
Performance of two types of
sprinkler irrigation emitters
In a WRC supported project, two
types of sprinklers operating on a
dragline and a Floppy sprinkler on a