Design of Small-scale Surface Irrigation the Case of Jalele, Ethiopia
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Date
2021-04
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Addis Ababa University
Abstract
The project Jalele small scale irrigation is located in East Wollega Zone, Sibu Sire Ana, at a distance of about 37km away from Nekemte, nearby Nekemte-Finfinne high way. The area of the catchment (watershed) is 17km2 and the project is intending to develop 60 hectares of land by surface irrigation.
The overall objective of the project is to design and analyze of small-scale surface irrigation by using river water (Jalele river). Specifically, design of surface irrigation, design of head work (weir), and selection of weir type will be the major one performed in this project.
The necessary data that was collected and used for this study were primary and secondary data. Data essential for this project work was collected from different sources. The collected data include soil, agronomy, hydrology, geology, surveying that is used for headwork, main canal, and irrigation system design.
During peak flow, the water level attained is equivalent to 0.90m. The water level is obtained from stage ~ discharge curve. After preparing stage ~ discharge curve, the tail water depth is estimated as 0.90m. For stage ~ discharge curve, the discharge was calculated by using Manning equation, Q = (A/n)*(R2/3 I 1/2).
Expected maximum flow for Jalele catchments is estimated by Rational Method Qp = 0.00216 CIA0.73 = 0.00216 * 0.63 * 96mm * (1700ha)0.73 = 29.8 m3/s ≈ 30m3/sec, based on field data observation, i.e. land slope classification, coverage of the area, and value of runoff coefficient, C. Thus, high flood level of the river (HFL) before construction of the structure is, HFL = river bed level + tail water depth = 1861.30 + 0.90 = 1862.20.
Ogee weir is selected from broad crested weir for big boulders are coming from upstream mountainous area. Other reason for selecting ogee weir is due to its high coefficient of discharge. Ogee weir is used to pass boulders coming from upstream easily.
Furrow surface irrigation, the most common method of surface irrigation, is recommended for this project, for the following reasons; it is suitable to the soil type of the project area; it has been traditionally exercised by the farmers of the project area; it is easily manageable at farmer’s level; and it is suitable to irrigate all crops, which are recommended for the project.
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Keywords
Small-Scale Surface Irrigation, Design, Jalele, Ethiopia