Water Delivery Performance at Metahara Large-Scale Irrigation Scheme, Ethiopia
UNESCO-IHE Institute for Water Education, Delft, Netherlands; Water Resources and Irrigation Engineering Department, Arba Minch University, Arba Minch, Ethiopia
Water distribution, delivery and hydrodynamics in manually operated gravity irrigation schemes are often complex. The nature of the hydrodynamics and its impacts on water delivery are generally not well understood by operators. The Metahara Irrigation Scheme, Ethiopia, with a gross irrigated area of 11 500 ha, is an example of such a scheme. This paper assesses water supply and demand of the scheme and evaluates the water delivery performance to 15 offtakes at head, middle and tail reaches of a 10-km-long canal. Adequacy, efficiency, equity and dependability were used as indicators of water delivery performance. Results indicated that average annual irrigation supply is in excess of demand by 24%. Water delivery at tertiary levels was adequate in terms of quantity, and suggests insignificant field losses. However, a significant amount is lost in the conveyance and distribution canals and to saline swamps at tail ends. Unlike claims of water shortage, the major water management challenge is lack of sound operational rules, which made the delivery inequitable and inefficient. Delivery was inferior in terms of adequacy and dependability at middle reach offtakes. Optimal water diversion and distribution not only save water, but also reduce the danger of waterlogging and salinity in the scheme. © 2015 John Wiley & Sons, Ltd.