APPRAISAL OF DESIGEN PRACTICE AND FAILURE OF RIVER DIVERSION FOR IRRIGATION SCHEMES: A CASE OF WADLA WOREDA NORTH WOLLO, ETHIOPIA

Abstract

Wadla woreda is located in south western parts of north wollo zone at latitude of 11°36'35.03" N and longitude of 38°55'54.06"E. This study appraises the design practice and failure of the river diversion structure for irrigation in the study area and identifying, analyzing and categorizing of the main problems were focus points. This study considered by selecting five existing river diversion structures in different Kebeles of the woreda to understand the causes of the major failures of the structures by considering different aspects such as pre- and post-construction, institutional aspects, planning problems, social and operational problems and initial design documents. In order to identify and characterized the existing irrigation schemes field observation and measurements, group discussions, interview and questionaries’ were used to achieve the objectives of this study and analyzed by SPSS statistical software. Arc-GIS 10.1 was applied to delineate the watershed of the study area, pick discharge estimated by Soil conservation system (SCS) and Auto CAD -2007 used for design purposes. The design practice of the studied area is very poor. In these study areas most of the implemented schemes are suffering from problems attributed to design, construction, and operation & maintenance that lead to major failure of the structures. From the analysis the maximum value of hydrology and sedimentation consideration, hydraulic design of weir and structural design of weir problems showed that 31%, 49% and 20%, respectively. Based on the questioner, interview and group discussion, results the maximum value indicates absence of project idea of the community, water user association and lack of community participation on construction are 100%, 96% and 100% respectively. Finally, failures were due to the problems in the hydrologic, hydraulic and structural design of diversion systems in addition to improper management of the schemes.