THE APPLICATION OF SAPWAT MODEL IN IRRIGATION WATER MANAGEMENT PLANNING FOR THE SAND-VET IRRIGATION SCHEME: CONTRIBUTION TOWARDS AN INTEGRATED CATCHMENT MANAGEMENT SYSTEM

Determinations of river basin (catchment) water balances are currently difficult due to lack of information on crop water requirements, irrigation practices and management, particularly with respect to the efficient use of irrigation water. Effective application of irrigation water management on an irrigation scheme requires knowledge of how much and when the crops require water. Furthermore, the irrigation manager needs to know which portion of the irrigation requirement of crops is added by rain and what must be added as irrigation. A provision must also be made for salt leaching and system efficiency. Moreover, the irrigation farmers and water user associations or other water management bodies must know how much water is available for irrigation and how the water requirement is distributed over the year. The SAPWAT (South African Procedure for estimating irrigation WATer requirements) model was used for the determination of water and irrigation requirements of crops in the Sand-Vet irrigation scheme with the objective of contributing towards efficient utilization of water in agriculture. The application process of the SAPWAT model is done in three phases: (1) determination of the irrigation requirements of individual crops, (2) determination of the irrigation requirements of sub-catchments, (3) determination of the irrigation