INVESTIGATION OF THE CAUSES FOR MALFUNCTION OF MECHAWA SMALL SCALE IRRIGATION SCHEMES, OROMIA, ETHIOPIA

Abstract

Ethiopia faces a number of challenges in the development and management of irrigation schemes, including biophysical, technical, socioeconomic, and institutional factors. Many developed irrigation Schemes have been failed due to design fault, lack of adequate data, inadequate participation of stakeholders, and watershed degradation. The study was carried out to assess and identify the causes of the Mechawa diversion weir failure which is one of the Chiro district irrigation schemes. Thus, the encountered causes can be used for a variety of purposes, including the construction of a new diversion structure (either as a replacement for existing structures or as an entirely new structure), and existing structure rehabilitation. In this study, Hydraulic and hydrologic failures of scheme were assessed using collected primary and secondary data. The collected data were analyzed using ArcGIS, Micro soft excel, and SPSS software. The failure of the scheme due to hydrologic data was evaluated using the SCS CN method. The hydrological analysis has been conducted based on 21 years of maximum daily rainfall data. The frequency analysis has been carried out by different methods and the Gumble EVI method is adopted to estimate daily point rainfall. The peak discharge computed by (USSCS) method using estimated point rainfall is 204 m 3 /sec for the scheme. Since the peak discharge mentioned in the design document which means 190m3 /sec was underestimated, the peak discharge calculated by the SCS curve number method is adopted. According to the results obtained using SPSS software, 46% respondents confirm that there was poor study and design, and 24% poor selection of competent contractors and supervision gap, 64% poor community participation during planning and implementation. On other hand, an attempt was made to understand the design problems concerning hydrologic, hydraulic, and structural design aspects using secondary data. The problem of inefficiency in irrigation schemes can be emanated from technical and nontechnical factors like poor community participation, poor scheme management, and absence of operation and maintenance. Therefore, it is essential to accord due consideration to these issues to properly address the problems and to design the correct operational strategy. Finally, the restudy and redesign should be done from minor repair to full re-engineering Measures are recommended