Evaluation of Irrigation Water Measurement Methods and Devices in South Africa

A three year long research project, funded by the Water Research Commission of South Africa, commenced in 2001 with its main objectives being to assess the current status of irrigation water measurement in South Africa and to establish guidelines for the correct choice and management of flow measurement devices for irrigation water from different distribution systems (canals, pipelines and rivers). An assessment of the current situation identified one of the biggest problems in practice to be the measurement of water abstracted from rivers by individual farmers using motor-driven pumps. The remoteness of the sites, the quality of the water, the complications of pumps being privately owned, and the general resistance of the farmers to having the water measured have in very few cases been overcome by the WUAs in their search for affordable, reliable and tamper-proof measuring devices. As a result, two methods of indirect measurement for estimating water use are being investigated, firstly measuring and recording the pressure on the up-stream and downstream sides of the pump and relating it to the actual discharge through calibration, and secondly, measuring and recording the power consumption of the pump and relating it to the actual discharge through calibration. The paper addresses the results of these evaluations and how they contribute to the formulation of guidelines for WUAs on issues such as required accuracy of measurement methods and devices, automation of measurement systems, performance of devices compared to conventional meters as well as cost-effectiveness of new approaches.