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.
