Abstract:
In the semi-arid part of central South Africa, population growth and industrial
development are the driving forces for an increased demand for water. This accentuates
the need for wise decisions by catchment management agencies (CMAs), especially
in water scarce semi-arid areas. These decisions become more and more complex
as the range of demands widens over the spectrum of water consumers, i.e.
municipal, industrial, irrigation and rainfed farming. A study was conducted in the
Upper Modder River catchment which is situated in the semi-arid area of central
South Africa, where crop production in the catchment using conventional production
technique is currently not suitable due to marginal and erratic rainfall. Moreover, the
area is characterised by low precipitation use efficiency as a result of large runoff and
evaporation losses on clay and duplex soils. A labour intensive in-field rainwater
harvesting (IRWH) technique recently introduced into a part of the basin occupied
by small scale farmers has been shown to increase maize and sunflower yields by 30
to 50% compared to conventional tillage, making it a feasible option for the these
farmers in the catchment. The area of land suitable for the IRWH located in the
communal land is estimated to be 23 000 ha. Two catchment management options
presented in this paper are: option-1: allowing the IRWH suitable land in the communal farming area to remain under grassland and utilizing the runoff downstream
for irrigating maize; option-2: utilizing the IRWH suitable land for maize production
in the basin, using the IRWH technique. Results showed that the expected maize
production from option-2 was higher than from option-1. A financial analysis also
showed that gross margin, expressed as Rand per m3 of rainwater utilized, was between
0.0234 to 0.0254 under option-1 and 0.0354 for option-2. This clearly shows
that use of rainwater where it falls has high socio-economic benefits for the communal
farmers who are currently struggling to achieve sustainable livelihoods.
