I
Felix Reinders
ARC-Institute for Agricultural Engineering
t is imperative that an irrigation
system must be designed correctly and managed properly to
optimise yields. Irrigation implies that water is applied artificially
to supply in the crop’s needs and
irrigation water managers from farm
level to scheme level, as well as designers of irrigation systems use a
planning tool for water requirement
estimates to enable them to supply
the right amount of water at the
right time to a crop. This tool is
called SAPWAT (short for South African procedure for water requirements) and was developed in South
Africa.
good planning and management of ning.
irrigation water is of utter imThe weather data included monthly
portance to increase the efficiency of
data and have up to fifty years of
irrigation water use.
daily data in 5100 weather station
This user-friendly computer model
data sets with an amount of more
has been developed that enables
than 38 million records. This allows
irrigation water users to plan the
SAPWAT3 to be used internationally.
amount of irrigation water required Daily data for any number of succesby irrigation farm, an irrigation
sive years is used to do year-on-year
scheme or a water management area irrigation requirement estimates, the
on a month by month basis. SAPresult of which allows the user to
WAT, was first published and used in include risk analysis as part of the
1999. It was a further development
planning process.
of CROPWAT and is used by more
It furthermore include 2500 crop
than 300 users in 13 countries, even
records by providing for differences
though it was designed against the
in growth and development because
background of South African needs.
of planting different cultivar types at
Good planning of irrigation water
SAPWAT was continuously improved
different times of the year and in
requirements for the irrigation indus- and upgraded, with the newest verdifferent climates. Irrigation stratetry advance the overall management sion published as SAPWAT3. SAPgies can be varied to demonstrate
of water and its distribution beWAT3 is based on the Food and Agthe effect of different strategies on
tween human, industrial, irrigation
ricultural Organisation’s Irrigation
irrigation requirement. This allows
and environmental requirements. In and Drainage Paper no 56, “Crop
the user to devise irrigation strateSouth Africa, where a number of the Evapotranspiration”, which reflects
gies that will aim at maximizing rainmajor rivers are already overthe international thinking on the
fall use efficiency and thus reduce
extended, and where irrigation uses standardization of approaches to
irrigation water requirements.
about 60% of the total water supply, irrigation water requirement planSAPWAT3 (see figure 1) is designed
for maximum user interaction with
an approach which contributes to
the user’s understanding of issues
affecting good irrigation water
planning and management. It is
not a crop growth model but it is
designed to allow the user to imitate through interaction the situation in an irrigated field. This allows the user to do “what if” with
different irrigation scenarios to see
what the effect of a specific management decision is on irrigation
water requirement.
Figure 1: SAPWAT software