A THESIS SUBMITTED TO THE FACULTY OF WATER RESOURCE AND IRRIGATION ENGINEERING, WATER TECHNOLOGY INSTITUTE, ARBAMINCH UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN IRRIGATION AND DRAINAGE ENGINEERING

Abstract

Evaluation of the performance of irrigation schemes facilitates is required to portray condition of the scheme and to apply possible remedial measurements. West Gode irrigation scheme is located in the Somali Regional State of Ethiopia and was constructed in 1987 GC. Even though this scheme has existed for more than three decades, the performance of the irrigation scheme has not been evaluated yet. In this study, the performance of the scheme was evaluated by estimating the water delivery performance of the scheme based on external indicators such as water conveyance efficiency, and water conveyance losses as well as the internal indicators such as water application efficiency, distribution uniformity, storage efficiency, and deep percolation losses. Primary data was collected through field measurements and scheme observation such as measuring canal dimensions, flow, infiltration rate, whereas, secondary data was collected from different sources which include a meteorological office for the historical temperature and other documents for referencing. The water conveyance efficiency of the main, primary, and secondary canals and also conveyance losses were estimated by measuring irrigation water flow at different canal reaches i.e., upstream, middle, and downstream points. The estimated overall water conveyance efficiencies of the main canal, two primary canals, and three secondary canals were 77.9, 72.8, and 69.1%, respectively. The result of internal indicators for application efficiency, storage efficiency, distribution uniformity, deep percolation ratio, and overall efficiency were 54.93, 92, 94.9, 45.067, and 38.73%, respectively. High water wastage was noted mainly upstream of primary canals due to canal breach, poorly managed canal gates, and water misuse, resulting in low canal conveyance efficiency. Similarly, significant water loss occurred at the field level due to deep percolation. To improve canal efficiency, canals should be lined and cleaned from plant debris also community awareness is required with supervision and monitoring to stop canal breaching.