Service Contract No 2007 / 147-446 NYANYALI ... - Swaziland

Two sprinkler packages with two different nozzle size combinations were identified as shownin table 3 above. Flow variation due to the different sprinkler – nozzle combinations is 55.87%and is not in line with the ARC recommendation stating that the difference in discharge in aspecific irrigation block may not vary by more than 10% from the average discharge. Theaverage application rate of the above combination is 1.16m³/hr and is lower than the designapplication of 1.4m³/hr. These figures indicate that even on highly efficient pumping andsupply system, irrigation efficiency will not improve, at least not until uniformity in this regardis obtained. This different combination has an effect also on the wetting diameter due to theirdifferent body trajectory angles.Nozzle wearingMeasurements of the amount of sprinkler nozzle wear (mm) averaged 1.4% reaching amaximum of 2.1%. An increase of 5% in nozzle area means a 10% increase in flow andpower demand, which means additional operating costs and over-irrigation. The ARCtherefore recommends sprinkler replacement if wear is greater than 5%. This irrigationsystem has been operated for only 7 years.Sprinkler nozzles were measured with a specially machined apparatus (Figure 14)Figure 15. Measuring apparatus for sprinkler nozzle sizeNyanyali Farmers Cooperative Report - 2009 Page - 27 -