PERFORMANCE OF IRRIGATION SYSTEMS IN SOUTH AFRICA - Management, Performance, and Applications of Micro Irrigation Systems - page 60

5.1 INTRODUCTION
The process of efficient irrigation water management includes determination and the
control of rate, amount, timing and distribution of irrigation water so that the crop
water requirements are met in a planned and effective manner. This not only depends
on the correct technical and agricultural design but ultimately also on the standard of
management and maintenance of the irrigation system.
This chapter presents the status of the performance of irrigation systems that was
determined by evaluation of irrigation systems in fi ve sugar growing areas of South
Africa by the Agricultural Research Council of Institute for Agricultural Engineering
(ARC-IAE, 1), on behalf of the South African Sugar Association.
Thirty-eight systems were evaluated, such as: Overhead (sprinkler and flop-
py), center pivot, micro and drip-(surface and subsurface)-irrigation systems. The
target areas in South Africa were Malelane, Komatipoort, Umfolozi, Heatonville
and Pongola. Although the performance of most of the irrigation systems was
lower that the accepted norms, yet it was within the normal range for in-field
evaluations.
5.2 IRRIGATIONEFFICIENCY
The irrigation efficiency is difficult to define since it is a concept that represents
the maximizing of inputs. This concept requires the evaluation of many factors
that influence the overall performance of an irrigation system. These factors are
definable, but are specific for each situation. Figure 1 shows these efficiencies
schematically and it is important to understand these, the factors that influence
it, and how to apply these. Figure 1 reveals that water movement through an ir-
rigation system, from its source to the root zone, is regarded as three separate
operations: Conveyance, system distribution and field application. Conveyance
is the movement of water from its source through the mains and sub mains or
canals to the farm block off-takes. System distribution is the movement of water
through the distribution system or canals to the emitter outlets and on to the soil
surface. Field application is the movement of the water from the emitter outlets
into the root zone of the crop. With the evaluations, only the system efficiency
was addressed.