TECHNICAL PERFORMANCE EVALUATION AND REDESIGNING OF KETAR MEDIUM SCALE IRRIGATION SCHEME, SOUTHEAST OF OROMIA REGIONAL STATE, ETHIOPIA

Abstract

Irrigated agriculture produces about 40% of all food and fiber on about 16% of all cropped land. Low level of performance can be identified at any level and stage of irrigation systems. Improving irrigation performance to increase productivity is one of the main visions formulated by national and international organizations involved in water development. Evaluation of performance of irrigation systems has been increasingly stressed in recent years by many researchers and managers of irrigation schemes. This study was aimed to contribute to the improvement of irrigation efficiency and crop productivity of the farm. It had been conducted on Ketar medium scale irrigation scheme situated in Arsi zone Oromia Regional State of Ethiopia. To test performance of the scheme irrigation performance indicators, namely, conveyance, application, storage efficiency, water application uniformity, depletion fraction, runoff ratio, deep percolation, irrigation water use efficiency and scheme sustainability were done. It has three stations; Ketar-1, 2 and 3 and designed for 860 l/s discharge to irrigate 400 ha of land, whereas current measured discharge was found as 800l/s and was irrigating about 541.40 ha. The reason of discharge reduction is flow fluctuation due to climatic change. Potato was the selected crop for the experiment. Soil of the study area was found clay loam, moderate acidic, non-saline soil and has 3.44OM in average. Average Ec, ,Ea, Eu, Es, DF,RR,DPF,IWUE of Ketar scheme was found as 57.4%, 61.6%, 61.6%, 160%, 70.1%, 27.86%, 10.54% and 2.38kg/m3, respectively. Redesign was done due to low conveyance efficiency and existence of runoff and deep percolation loss. Design of lined secondary canal with flow of 0.518m3/s was made. New reservoir of capacity 26,891.2m3was also designed due to silt accumulation for previous one. The study was concluded as upper and middle stream users were consuming more water than the lowers with decreased productivity of the scheme and technical support and SWC activities in this watershed are recommendable for sustained design discharge.