PERFORMANCE EVALUATION OF TIBILA IRRIGATION BASED DEVELOPMENT PROJECT DIVERION HEADWORK, ETHIOPIA

Abstract

Headworks usually function as the key facilities for irrigation projects, and many of them are being designed and constructed, and in the previous years too. However, their performance capacity to the intended design level is still not satisfactory. To this end, performance evaluation of Tibila irrigation project diversion headwork, found to be a crucial research matter. An approach is made to investigate the prevalence of constraints that cause the diversion headwork`s underperformance and to understand the hydraulic and structural problems occurred. This will help as a basis for securing function of the Tibila Headwork and any other Headwork`s under operation. Through giving an insight of performance issue in view of functionality of the Headwork to assure schemes sustainably functioning, for concerned parties/organizations. Field survey has been made to understand the current conditions of the scheme headwork. Through the observation the causes on the structure that exposed it to under performance and their consequence on the project as a whole have been identified. Whereas the surveying work and various cross-section measurement was also done which helped to determine the prevailing problem of crest removal, sedimentation around the approach canals and intake gates which resulted in gate clogging, trash rack breakage and reduction of flow figuratively. The main factors observed leading Tibila diversion headwork for underperformance recently, which will hinder its performance in the future too are improper location of the approaching pipes, intake gates, undermining or usage of inadequate dimensions of approaching pipes, dimensions of the vertical drop/Sarda fall settling basin length and width during design, and severe sedimentation due to location of the intake with in short distance from the diversion i.e. not enough transition length for flow regimes, damage on trash rack, which resulted in clogging of intake gate, crest removal, relatively high operation and maintenance cost for sediment removal/flushing year to year etc. Moreover, crest removal is also causing disagreement with Awash River basin management Authorities due to the refilling work to attain the design crest level (i.e. the top end elevation level of the diversion fixed during design) of the diversion headwork during occurrence of overtopping associated with flood in addition to being a cause for reduction in hydraulic performance of the Headwork