A COMPARATIVE EVALUATION OF IRRIGATION EFFICIENCIES FOR SMALLHOLDER IRRIGATION SCHEMES IN MURANG’A SOUTH DISTRICT, KENYA

Abstract

Irrigation schemes are usually designed and implemented on the basis of assumed efficiencies in water application, water conveyance, and water distribution. However, over time, physical changes in the schemes such as poor maintenance of structures, soil property changes and deterioration of equipment may alter these efficiencies. It is therefore imperative that the efficiencies are periodically evaluated as a way of monitoring and evaluating the irrigation scheme. This study identified the irrigation technologies the farmers were using and evaluated the water flow rates and efficiencies of several smallholder schemes in Murang’a South District to ascertain whether these schemes were operating at their design recommendations and efficiencies. Water flow rates were measured using Parshall flumes, while soil water statuses were measured with tensiometers. Social economic data was collected using structured questionnaires. The results showed that the sampled schemes had high water conveyance efficiencies (95%). This was attributed to the use of pipes and lined canals in the main conveyance systems. Distribution efficiencies ranged between 76% and 95% while application efficiencies varied between 58% and 86%. The overall efficiency was between 44 and 77%. The water application uniformity was generally below acceptable limit, ranging between 41 and 71%. The low water application uniformity was attributed to the improper overlapping and spacing of sprinklers. It was therefore recommended that the farmers be retrained on the proper layout, spacing and overlapping of sprinklers in addition to water saving technologies in irrigation.