Irrigation & Drainage Systems Engineering

The primary objective of this study was to assess the land resources potential of the Shaya River sub-basin in the Bale Zone of Oromia for irrigation and providing a geo-referenced map of these resources. Watershed delineation, identification of irrigable land, and estimation of surface runoff and irrigation water requirements were the steps followed. Irrigation suitability factors such as slope, texture, depth, drainage characteristics, land use/cover and distance to water source were taken in to account to identify irrigation suitability. The suitability analysis of the parameters indicates that 66.38% slope, 98.20% soil, 92.93% land use/cover of the study areas classified as potentially suitable for irrigation development in the study area. By weighing analysis of all parameters 22.05% of the study area was found to be highly suitable, 25.27% moderately suitable and 16.20% marginally suitable whereas about 33.57% restricted for irrigation developments. By comparing the required water and available monthly flow of the river, the river has the capacity for the application of the command area.

Evaluating the performance of irrigation systems will assist to distinguish whether the targets and objectives of the irrigation projects are met or not. In this study, a comparative performance evaluation was made on two small scale irrigation schemes in Adami Tulu Jido Kombolcha district Oromia Regional State Central Rift Valley of Ethiopia. The irrigation schemes were Haleku scheme with a command area of 42 ha and 96 beneficiaries, and Dodicha scheme with 75 ha irrigable lands and 150 beneficiaries. Primary and secondary data were collected for the study. The primary data include discharge at diversion point, moisture contents of the soils before and after irrigation, measurement of depth of water applied to the fields. The secondary data include total yields, farm gate prices of irrigated crops, area irrigated per crop per season, crop types, incomes generated by the irrigation associations, investment costs and cost of production and metrological data. The two-irrigation schemes were compared using the IWMI (International Water Management Institute) minimum sets of comparative indicators. The comparative indicators used were Agricultural performance, water use performance, Physical performance and Economic performance. From the analysis of Agricultural outputs, the outputs per cropped area were found to be 2,852.77 US$/ha and 2,179.41 US$/ha for Haleku and Dodicha irrigation schemes respectively, but the values of the output per command area of the schemes in the same order were 2,852.77 US$/ha and 1,278.59 US$/ha. The output per unit irrigation supply of Haleku was 0.18 US$/m³ and of Dodicha was 0.13 US$/m³. Output per water consumed was 0.53 US$/m³ and 0.43 US$/m³ for Haleku and Dodicha irrigation schemes, respectively. With regard to the water use performance, water supply and relative irrigation supply were found to be equal which amount 2.89 and 3.34 for Haleku and Dodicha schemes respectively since all the water is supplied through irrigation; there was no rain fall during the study period. The irrigation ratio of Haleku is 1.00 which means 100% of command area was under irrigation and that of Dodicha was 0.59 which means about 41% of command area was not under irrigation during study period. The gross return on investment was 2.33 and 4.66 by ratio for Haleku and Dodicha irrigation schemes respectively. The financial self sufficiency of both schemes show that 5.29 for Dodicha scheme and 27.76 for Haleku scheme. In general, based on the assessment carried out, it can be concluded that the Haleku irrigation project performs better than Dodicha scheme. For improved performance of the schemes, farmers should share operational experience to one another, and get water management training. Further, it is good to provide simple hydraulic flow metering structures on the canals to monitor water supply and utilization.

The study was done to assess the overhead irrigation system performance of dragline sprinklers at Finchaa, Eastbank sugar estate irrigation scheme using water distribution uniformity indicators, sprinkler discharge efficiency and variation of system discharge and operating pressure. The measurements of sprinklers water distribution uniformity were made for overlapped sprinklers at recommended spacing of 18 m × 18 m at head, middle and tail end of lateral lines for selected field at different locations of the command area. The estimated values of uniformity coefficients (CUc) and distribution uniformity (DU) along the laterals from head to tail ends varied from 71.8 to 82.8% and 66.6 to 74.3% respectively. The water distribution uniformity decreased from head end to the tail end of the lateral lines and was not satisfactory at middle and tail ends of the laterals. The sprinklers discharge and pressure along the lateral line from head end to tail end varied from 6.1 to 14.3% and 9.4 to 24.1% respectively. The values were higher for field having longer laterals (360 m to 410 m) as compared to the fields having shorter laterals (260 m to 295 m). The sprinkler discharge efficiencies varied from 87.08 to 92% and the values were slightly lower than the proposed ranges. The sprinkler spray losses were higher due to high evaporation during the test.