Conjunctive use of canal water and groundwater for sustainable irrigation in command areas

Abstract:

A trend that irrigation managers across southern Africa can’t ignore: canal systems designed decades ago now deliver water for only 5-7 months of the year, leaving crops stranded during the remaining dry months. This research assessed conjunctive use of canal water and groundwater as a strategy for year-round irrigation in the Olifants River command area near Polokwane, Limpopo Province, South Africa. Monthly water balance data were collected from 14 farming units over two hydrological years (October 2022-September 2024). Canal supply met just 58.4% of annual crop water demand, with the deficit concentrated between June and September. Groundwater pumping filled 34.1% of the gap, raising total water availability to 92.5% of demand. Conjunctive-use farms achieved 31.8% higher seasonal crop yields than canal-only farms. The benefit-cost ratio for borehole installation was 2.46 over a 10-year amortisation period. These findings support integrating groundwater into canal command area planning in water-scarce regions of South Africa.