Evaluating and enhancing irrigation water management in the upper Blue Nile basin, Ethiopia: The case of Koga large scale irrigation scheme

•Reservoir water volume evaluated with respect to demand.•Irrigation water demand and supply evaluated for the irrigation system.•Cropping preference for the irrigation system assessed and discussed.•Evaluation of scheme performance with respect to canal inflow and outflow conducted.

sThis paper deals with the objective of evaluating and enhancing irrigation water management of Koga large scale irrigation scheme located in the Blue Nile basin of Ethiopia. Disturbed and undisturbed Soil samples were collected from selected irrigation blocks within the irrigation system. Soil moisture, texture, field capacity, permanent wilting point and bulk density data were obtained from laboratory analysis of the samples. Results of demand versus supply analysis of the scheme showed that there was excess supply at the beginning of reservoir release and upto 7.13 MCM of excess flow water was estimated in year 2015. Results also showed that crop water requirement value varied for each block and for different crops in the same block, assuming the climatic conditions of the site constant. The crop water requirement variations were caused by differences in soil water holding capacity of each block. Based on crop water demand analysis result with appropriate crop water provision of 50% efficiency, the maximum irrigable area which could be accommodated by the reservoir storage was 5635.8 ha as compared to the design command of 7000 ha. The paper also investigated the status of reservoir water availability as compared to the demand and annual release. The findings of this research will have greater implications in creating awareness to the water user associations, farmers and gate operators of Koga irrigation scheme on how to measure the amount of water they are using during the whole crop growth so that optimum irrigation water shall be delivered to a crop for maintaining water management.