Koga irrigation scheme water quality assessment, relation to streamflow and implication on crop yield

Abstract

The Koga irrigation scheme is the first attempt of eleven major proposed large-scale irrigation schemes in Lake Tana sub-basin in the Upper Blue Nile Basin. The schemes are to provide water for small holder farmers. The completion of Koga scheme poses various challenges and provides important lessons in implementing and operating large-scale irrigation projects. With anticipated increased agricultural productivity, one of the foreseeable challenges will be the continuous assessment of the water quality. This study assesses the quality status of Koga River by analysing samples collected from planned sampling locations. Two sampling campaigns were undertaken, and 23 physical and chemical water quality parameters were measured using standard methods. On the basis of FAO irrigation water quality guideline, Koga irrigation water is well within limits of salinity, sodicity and toxicity hazard except above the threshold value of boron. Among the dominant crops cultivated potato, barley and wheat production are susceptible to yield reduction. A detailed investigation is required to quantify the extent of yield reduction incurred due to higher level of boron. Multivariate statistical technique is applied for the evaluation of relationship between streamflow and various water quality parameters.