Catchment management in semi-arid area of central South Africa: Strategy for improving water productivity

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.