An evaluation of irrigation water supply infrastructure to improve conveyance efficiency and water availability at Dzindi Irrigation Scheme, Limpopo Province

Abstract

A water use and availability study was conducted at the Dzindi Irrigation Scheme in Limpopo Province. The problems experienced at Dzindi Irrigation Scheme regarding water allocation, concern water availability at a field level. Although water is continuously being diverted into the main canal, farmers at the bottom end of the system claim not to receive adequate water supplies, forcing them to practice dry land irrigation (farming). Water losses occur between the source and the point of application, and the causes of loss need to be identified so that water availability can be improved. The study focused on water released to Block 2, and an analysis was made of all losses which occur from the weir where water is released to the point of application in the fields. An estimation of water supplies that return to the river as an unused delivery, and conveyance losses that occur along the distribution channels, were determined through a water balance drawn up from measured canal inflows, such as seepage and evaporation. A total volume of 371096 m3 was supplied to Block 2 during a 45 day monitoring period. For a planted area of 16.52 ha, this works out to 22463 m3 /ha supplied, or a relative irrigation supply of 14.2 times the irrigation requirement. Losses originate from a number of sources. Results indicated that losses that occurred in the main canal were very low, with a conveyance efficiency of 96% recorded. Knowledge of irrigation water management and practical irrigation scheduling at a scheme level is weak. The biggest immediate need is to improve the management of the infrastructure. The main system capacity is adequate, and losses due to seepage, evaporation and return flows are within acceptable limits. The return flows are mostly caused by the farmers’ lack of understanding that led to them removing the entire sluice gates at the head of the secondary canals of Block 2. This results in water running to the first two secondary canals only, and not reaching the rest of the Block. Based on the requirements identified by all the stakeholders, training should be provided to the water bailiffs and farmers to implement management practices that are both effective and sustainable. Together with prioritised infrastructure upgrading, more acceptable water delivery should be possible. The challenge lies in making the technical and the social aspects converge in such a way that the result is acceptable to both systems and can be sustained over time. The opportunities for capacity building by equipping thestakeholders with new skills are considerable, but the time and effort required to achieve this should not be underestimated.