Abstract
In designing a canal system, a major problem is to decide what conveyance parameter to apply in the calculations. Since basic knowledge on this subject is lacking, it is usually taken from literatures. Most of the irrigation projects in Ethiopia are found to work below their expectation. One of the main reasons is the conveyance parameters variation from the expected (design) value which ultimately affects the envisioned conveyance efficiency. To evaluate this variation, Fentale irrigation scheme was used as case study. The conveyance efficiency used at the design stage was 80%, which was within Food and Agricultural Organization of the united nations recommendations; while the field survey value was 17%. Such huge variation was due to the fact that the assigned conveyance parameter values (roughness coefficient, hydraulic radius and bed slope) no longer represent the current situation of the scheme. Such variation has resulted in increase in the depth and top width of the water surface which further resulted in 13% and 3% increase in wetted perimeter and top width of the canal, respectively. Thus this study suggests that conveyance parameters shall be derived from history of existing irrigation schemes in a country, rather than adopting it from standard literatures. As such construction quality, maintenance activities and technological transfer activities in a country shall be seen in deciding the conveyance parameters. The study also suggests that the ever increasing water shortage in an irrigation project could be managed by proper maintenance of the entire irrigation system.
Highlights
The conveyance efficiency used at the design stage was 80%, which was within Food and Agricultural Organization of the united nations recommendations; while the field survey value was 17%
This requires appropriate methods of measuring and evaluating how effectively water extracted from a water resource is used to produce crop yield [1], which intern shall start from the planning and design stage of an irrigation project
The expected and the actual value of conveyance parameters obtained for the main canal of Fentale irrigation scheme show great difference; 77% during design against the 17% existing conveyance efficiency obtained during the study time
Summary
Tefera 80 available water is more than that, due to high losses from storage, conveyance, and application to irrigation plots. Identifying the various components with their level of losses and knowing what improvements can be made are essential in making most effective use of vital water resource. As available water resources become scarcer, more emphasis is given to efficient use of irrigation water for maximum economic return and water resources sustainability. This requires appropriate methods of measuring and evaluating how effectively water extracted from a water resource is used to produce crop yield [1], which intern shall start from the planning and design stage of an irrigation project
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