EVALUATION OF IRRIGATION WATER MANAGEMENT IN THE LOWER AWASH RIVER BASIN, ETHIOPIA: THE CASE OF TENDAHO LARGE SCALE IRRIGATION SCHEME

Abstract

Evaluating and selecting improved and efficient irrigation water management practices are essential for enhancement of project or farm profitability by increasing the water productivity. However, in Tendaho large scale Irrigation scheme there is no a sound evaluation studies in the last few years. Therefore, this study was carried out to evaluate irrigation water management of Tendaho large scale irrigation scheme in the lower Awash River basin of Ethiopia, for improving overall irrigation water management, distribution and delivery in the scheme. The study also assessed basic procedures used to support sustainable irrigation water management practices. Primary data were collected through field measurements and survey, and secondary data were gathered from different sources. Disturbed and undisturbed Soil samples were collected from selected irrigation blocks within the irrigation scheme. Soil moisture, fieldcapacity, permanent wilting point and bulk density were analyzed in Tendaho Sugar Factory Research Center laboratory. Infiltration capacity was estimated using double ring inflitro-meter and the basic/constant infiltration rate was 0.4cm/hr. For determining and evaluating the performance of Tendaho large scale scheme, irrigation water performance evaluation parameters like adequacy, efficiency, equity and dependability were estimated. The discharges were measured using current flow meter at main canal, three primary, six secondary and twelve tertiary canals. The crop water requirement was estimated by CROPWAT-8 software. The results show that the overall Efficiency and Equity of water distribution of the system are not good and the adequacy of water distribution and dependability of the water supplied in the system is rated as good. The average Water surface elevation ratios at head, middle and tail reaches of the canal during the monitoring period were generally less than one, thus they show that the canal has a sedimentation/siltation problem. The result of Effectiveness of infrastructure shows, 18% of the structures were destroyed. So, this is signal for the need of maintenance or rehabilitation of canal structures. The result of Sustainability of irrigated area show that, currently from the total irrigable land of 25,000ha which was prepared for sugarcane production only about 9660ha was irrigated which means about 38% of the total prepared irrigable land. This is because of great social problems that are lack of trust on the project from the pastorals side, due to design and construction problems of canal, land leveling problem and different other problems accounted for minimized of irrigated land. Generally, for the long term sustainability, water distribution equity, reliability and water saving; continuous monitoring, maintenance and improvement measures are required