RESEARCH ADVANCES IN IRRIGATION METHODS FOR EFFICIENT WATER APPLICATION: SOUTH AFRICA - Management, Performance, and Applications of Micro Irrigation Systems - page 47

to simulate the hydraulics of flood irrigation more accurately [5]. In a WRC-sponsored
project, Russell [12] studied infiltration under flood-irrigation conditions on a typical
crusting soil of the Eastern Cape. He found that infiltration under dynamic (flood)
conditions on this soil was very high and remained so over the medium term, in sharp
contrast to the quick surface sealing and very low infiltration under static conditions.
4.3 COMPUTERIZED IRRIGATION DESIGN
An Israeli computerized irrigation design package was introduced in South Africa in
1983. 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 have been developed and re-
ported on. In 1987, MBB Inc. completed a WRC-supported project titled, 'The devel-
opment of procedures for design and evaluation of irrigation systems' [8]. Irrigation
design principles and procedures were studied in depth and evaluated critically. Dif-
ferent design algorithms were developed that were based on the well-known prin-
ciples of the PolyPlot software. The research eventually resulted in the development
of the IDES irrigation design and evaluation program, which was the front-runner for
the popular design program ModelMaker that was only introduced towards the end of
the century. Today a range of excellent computer programs are available for modern-
day design of efficient irrigation systems.
4.4 CONTAINING LOSSES DURING CENTER-PIVOT IRRIGATION
During the period 1970-1982, the efficiency of center pivot systems were estimated at
80%. A research project was supported by the WRC to investigate, identify and quan-
tify the spray losses between the emitters on a center pivot and the plant canopy [14].
Apart from technical measurements, meteorological and other factors influencing ir-
rigation 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 the wind speed 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 center pivots.
The WRC also sponsored a project aimed at deriving criteria for the adaptation of
overhead irrigation systems, including center pivots, to the infiltrability of different
soils, so as to minimize water losses through runoff and/or evaporation due to pond-
ing (1 to 4). The energy flux (or kinetic energy), given by a combined effect of drop
size, falling height and application rate was found to be a key factor. Equations were
derived for predicting the maximum allowable kinetic energy (MAKE) for different
scenarios [2].
4.5 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 ( Floppy Sprinkler Pvt. Ltd.) on a permanent layout were evaluated