EVALUATION OF FAILURES AND DESIGN PRACTICES OF RIVER DIVERSION STRUCTURES FOR IRRIGATION: A CASE STUDY OF TWO SELECTED SMALL SCALE IRRIGATION SCHEMES IN HADIYA ZONE, SORO WOREDA

Abstract

Many diversion headwork and pumps for small scale irrigation (SSI) schemes have been designed and constructed in preceding years. Some of them are performing successfully, but it has been observed in various reports and field observations that some of the schemes have failed to serve the purpose for which they are designed. Therefore, it is important to evaluate the failures and design practices of the two selected irrigation schemes (Awushoana and Kecha SSI) in Soro woreda. An attempt has been made to understand the design problems based on hydrologic, hydraulic and structural analysis for these selected two schemes. In addition, the main constraints that hindered the development of irrigation are planning, institutional, social and operational and economic problems were also addressed. This is needed to serves for different purposes such as for the construction of the new diversion structures (either as replacing for existing structures from minor repair to complete reengineering either to maintain existing function or to meet new requirement). The field survey has been made for these selected schemes to understand the current conditions of the schemes. The observation indicated which structures were seriously damaged. The different data’s were collected and used to analyze the main causes of failures of these two schemes. The main problems observed in Kecha SSI scheme were sedimentation of the head work, damage of intakes and sluice gates, clogging of intakes, damages of distribution systems (pipes) and the ram body. Whereas, the main problems observed in Awushoana SSI scheme were accumulation of boulders, collapse of diversion weir, damages of the intake gates, main canals and absence of the under sluice. Some of the problems attributed to the institutional, social and operational problems are lack of adequate community participation in planning and designing, absence of WUAs, proper handing over problem and lack of proper training and absence of proper maintenance, evaluation and monitoring issues. Another problem observed on Awushoana diversion weir was improper hydrologic analysis which in turn the problem of design of hydraulic structures. Therefore, peak discharge was estimated to be 122.66m 3 /s by using USSCS method using the daily annual maximum rainfall of 31 years of Hossaina meteorological station which is near to the project site. For this reason proper designing of the systems and increasing irrigation development activities based on farmers’ awareness creation makes the schemes more functional and sustainable.