Browsing by Author "Tirfessa, Tolera"

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    Small Scale Irrigation Project Structural Failures and Their Management Problems Related to Water Loss in Ethiopia
    (Addis Ababa University, 2017-06) Tirfessa, Tolera; Yilma, Sileshi (PhD)
    The challenges in reducing water losses of the conveyance structures such as earthen and lined canals were assessed considering the influence of participating parties (farmers, contractor and funding agencies) and contributing factors (hydrologic and hydraulic factors). The effect of conveyance efficiency, structural failure/performance, irrigation system management problems and water losses in Jemjem SSIP (which was constructed in 2004- 2006E.C), were the major problems for this study. The main objective of this study is to assess the reason why more than 50% of the water diverted is lost and to discover the solutions that can minimize the problems. To solve or estimate existing problems scientifically, the method proceeded are ‘measuring flow volume of the main canal at different points using v-notch weir to estimate loss in each interval and their conveyance efficiency, calculating Manning’s roughness of the main canal to compare with designed value of ‘n’, Estimating evaporation loss using energy balance method and estimating seepage loss of the main canal using Kostiakov A.N empirical formula and using some questionery results to estimate the influence of water management problems. The designed value was taken from the design report and the existing conveyance efficiency is obtained by measuring discharge and depth of flow of the canal at different locations. The conveyance efficiency given at the design stage was 90% for the scheme which was directly taken from FAO recommendations. However, the values obtained during the study were 34.9%. But, the conveyance efficiency selected should be based on construction materials, methods and qualities, managerial activities, technological and other factors affecting conveyance efficiency. The evaporation and seepage losses together constitute 3.63lit/sec while leakage and other operational losses account 23.07lit/sec/ (which is 56.27%) of the total main canal inflow. Such a decrease in conveyance efficiency or increase in water loss is found to be due to inefficiency of management issue and due to inefficiency of contributing factors such as construction material and (hydrologic and hydraulic factors). Thus, management problems, structural under performance and a designed conveyance efficiency taken directly from standard books had effect on the overall performance of Jemjem irrigation project. Irrigation structures should be maintained from time to time and Gates should be operated by trained operator to create equity of water distribution and also to make water management easy. Water shed management should be well implemented in the area so that quantity of silt deposited will be reduced. Water committee should be changed to WUA and sufficient follow up should be made to overcome water management problems existing in the project and similar projects in Ethiopia.