Awel SM, Tena Alamirew T and M
Abstract
Field assessment to evaluate the performance of small-scale irrigation projects plays a vital role in improving the existing projects and assist engineers in designing new systems so that irrigation practice becomes sustainable. This study was initiated to investigate the causes of under-performance of the Wesha small-scale irrigation project. The performance indicators that were used to evaluate the irrigation project are technical that directly or indirectly affect water deliveries and water spreading effects. Seven technical performance indices used; namely, conveyance efficiency, application efficiency, water storage efficiency, water distribution uniformity, deep percolation fraction, runoff ratio and sustainability. The evaluation was done using nine irrigation events on three representative farmers’ fields (selected from the head, middle and tail of the command area). During each irrigation event, water inflow and tail water outflow measurements; determination of soil moisture before and after each irrigation event; interviewing of irrigators; field observations and collection of secondary data were made. The results show that performance of the irrigation project is unsatisfactory in terms of conveyance efficiency, application efficiency, deep percolation fraction and sustainability with mean values of 65.39%, 46.78%, 48.43% and 30%, respectively. This shows that large volume of water is lost as steady-state and transient losses from canals and from irrigated fields. However, the distribution uniformity, water storage efficiency and runoff ratio are satisfactory with mean values of 88.3%, 97.63% and 4.45%, respectively indicating high deep-percolation loss. During the study period, on-site soil erosion, temporary water logging and illegal canal breaching are the observed major problems associated with the farmers’ irrigation practices. Weak operation and maintenance of the project is also witnessed and thus its sustainability is uncertain.