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

‣ Pump discharge is controlled mechanically by a butterfly valve. There is no Bermadhydraulic valve and the pump/motor has no safety mechanism e.g. no-flow switch.‣ The pump house is used as a storeroom and thus reduces working space and ventilationis compromised.‣ Only one pumping unit is installed operating 24/7. When this pump brakes sugarcanestands for weeks without water. This pump unit is occasionally serviced, especially at theend of the season; otherwise management attends only to breakages.MAIN LINE‣ No information was available on irrigation layout and pipe sizes and class. An undisputedconclusion, however, on whether the supply system was correctly designed or not can notbe drawn until precise details on pipe size, pipe classes, and distances occupied by thedifferent sizes are obtained. Accurate details are required also on the maximum areaavailable for future development and a hydraulic check conducted thereafter.‣ Mainline isolation valves are insufficient and some of those that are there aremalfunctioning‣ The main irrigation pipe works does not have enough air valves and those that are thereare leaking – overall system efficiency compromisedSPRINKLER INFIELD IRRIGATION‣ A complete system evaluation could not be conducted because the irrigation system wasshut down. The assessment was carried out after a period of heavy rains which not onlyraised the river level but also conceded a lot of iron oxide. According to Nyanyalimanagement irrigating during this time causes this material to accumulate inside thepipelines and in the long run reduces pipeline capacity.‣ Laterals of this dragline irrigation system are connected to the mainline through amechanical valve. For better performance of the system hydraulic valves must beinstalled instead and equipped with pressure-regulating pilots.‣ Two sprinkler packages with two different nozzle size combinations were identified and theflow variation due to the different sprinkler – nozzle combinations is 55.87%. this is not inline with the ARC recommendation stating that the difference in discharge in a specificirrigation block may not vary by more than 10% from the average discharge. The averageapplication rate of the above combination is 1.16m³/hr and is lower than the designapplication of 1.4m³/hr. This different combination has an effect also on the wettingdiameter due to their different body trajectory angles.Nyanyali Farmers Cooperative Report - 2009 Page - 35 -