Transmission Water Losses at South African Irrigation Schemes: A Case Study of the Vaalharts Irrigation Scheme

ABSTRACT Irrigation water supply is under scrutiny because of dwindling water resources. Most irrigation water in South Africa (SA) is transmitted by canals. Transmission water loss (TWL) accounts for 12% of the irrigation water losses in SA. Therefore, there is a need to investigate and understand the major parameters influencing TWL at Vaalharts Irrigation Scheme (VIS). A study using 39 concrete‐lined canal reaches was performed from 2020 to 2022. Water flow measurements and observations of selected environmental parameters with potential influence on TWL were performed on three occasions during the study. The velocity‐area method was used to calculate flow rates at the canal reach inlets and outlets. The inflow–outflow approach was used to determine TWL (% per 100 m). The study results revealed that TWL increased significantly ( p < 0.05) with decreasing canal size. Canal shape and location had no significant effects on TWL; however, the TWL decreased in the middle zones. Flow‐related parameters strongly affected TWL. Environmental parameters also exhibited strong effects. Although the study results elucidate TWL at VIS, further research involving more intense data collection is recommended. The effects of non‐physical parameters should also be investigated in future studies. Maintenance should be prioritized in irrigation schemes that use canals.