Evaluation of the Performance of Smallholder Pumped Irrigation Systems, in Arid and Semi-arid Areas of Kenya

Abstract

A study was carried out to evaluate the performance of smallholder pumped irrigation systems with a view of comparing if the system operated within the designed optimal engineering standards. Different parameters studied were selection, design and operations of the irrigation systems with detailed analysis on energy uses for pumping (fuel use), efficiency of pumping devices as well as pump power required and energy losses (headlosses) during pumping. Semi structured questionnaires were administered to 80 smallholder farmers practicing pumped irrigated agriculture in Mitubiri location of Kakuzi division and Kithimani sub location of Yatta division, Kenya. An observational study was done to identify the irrigation methods used. Detailed study was done in 10 farms (5 in each study site) using pumped irrigated agriculture and water application through furrow irrigation system. 79 % of the farmers assessed used small motorized pumps run by petrol and diesel fuel and ranging from 4.0-6.5 horsepower. Water was pumped from nearby rivers and conveyed to their farms using closed conduits, open channels or a combination of both.  Furrow irrigation method was widely used by 94% of the farmers studied in the two study areas. 60% of the irrigation setups using PVC pipes in water conveyance had the allowable water discharge within the design optimal range. The frictional head loss in the PVC pipes used exceeded the design limit for 60% of the irrigation systems while 90% of the irrigation setups used fittings whose resultant frictional head losses were within the desired optimal range. Of the 10 pumps evaluated, 6 of them operated below the optimal design efficiency level while fuel consumption rate of each pump varied. The study of the amount of fuel used to run the different pumps used in the 10 farm setups varied from one farm to the other. In some farms, mean fuel amount used to irrigate 1 hectare of land was in excess of 60L/ha while in other farm setups, fuel used was as low as 5L/ha. The varied fuel amounts used could be attributed to varied factors in each farm such as topographic elevations, water conveyance distance and different make and model of pump. An assessment of fuel consumption rate for each of the 10 pumps at similar operational speed was also different. Pumps age did not affect its efficiency. A comparison of the calculated pump power required and the power rated on the pumps being used showed a big difference indicating that the farmers used pumps which had a higher power rating than required. The effect of using an oversized pump is high initial cost of purchasing the pump as well as high operation costs due to high fuel use.

From the study, it was found that smallholder pumped irrigated agriculture despite showing tremendous increase in uptake faces numerous challenges ranging from components selection, design and use leading to poor performance.