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
