PERFORMANCE OF IRRIGATION SYSTEMS IN SOUTH AFRICA - Management, Performance, and Applications of Micro Irrigation Systems - page 69

5.7 SUMMARY
Irrigated agriculture is the largest user of water in South Africa and due to the pres-
sure on the limited amount of water, the efficient use is of paramount importance. The
environment in which irrigation farmers must function has also changed significantly
in recent years. In particular, changes in legislation that regulates the use of water, im-
pacts directly on irrigation practice. The National Water Act (Act 36 of 1998) provides
for water resources to be developed and for water to be protected, used, conserved and
controlled in a sustainable and equitable manner. This can only be achieved through
effective design, maintenance and management of irrigation systems.
The status of the performance of irrigation systems in South Africa was studied
through evaluations of irrigation systems in fi ve sugar growing areas of South Africa
by the Agricultural Research Council - Institute for Agricultural Engineering on be-
half of the South African Sugar Association.
Thirty-eight systems were evaluated which included overhead (sprinkler and fl op-
py), center pivot, micro and drip-(surface and subsurface)-irrigation systems. Malel-
ane, Komatipoort, Umfolozi, Heatonville and Pongola were the target areas.
Results indicated that the coeffi cient of uniformity (CU) was 72% for the dragline,
74% for the fl oppy and 89% for the center pivot systems, with the accepted norm of
84% or higher. The emission uniformity (EU) for the micro and drip systems was 72%
with the norm of 92% and higher. The average low quarter distribution uniformity
(DU) was 60% for the dragline, 67% for the fl oppy, 83% for the center pivot and 68%
for the micro and drip, respectively, with the accepted norm of 75% and higher. The
average application effi ciency (AE) was 76% for the dragline, 77% for the fl oppy and
82% for the center pivot. The statistical uniformity (SU) for the micro and drip sys-
tems was 74% with the accepted norm of 90% or higher.
Although most of the systems performed lower than the accepted norms, it is with-
in the range of what is normally found with in-fi eld evaluations. The impact, however,
is that with every 1% drop in CU, the yield might drop by 2%. The water use effi ciency
is also directly related to the application effi ciency and the results showed that between
24% and 18% of the water were lost due to evaporative and wind drift losses. The per-
cent of systems that had an acceptable DU were 100% for center pivot, 33% for drip,
5% for sprinkler, 0% for micro and 0% for fl oppy. Systems, that were well maintained
and correctly operated, generally had a high and acceptable DU.
The possible reasons, for the low percentage of the systems that comply with the
norms, can be a combination of incorrect pressures and spacings, worn nozzles, incor-
rect designs and climatic conditions with high wind speeds and temperatures. Con-
tinued evaluation and maintenance of irrigation systems are imperative to keep the
performance on a high level and to optimize water use effi ciency.