PERFORMANCE ASSESSMENT OF LARGE SCALE SPRINKLER IRRIGATION SYSTEM IN CASE OF ARJO DIDESSA SUGAR FACTORY, SOUTHWESTERN ETHIOPIA

Abstract

An Effective and efficient sprinkler system is combined effect of proper system design, careful operation, and timely maintenance and management, and it depends on its actual performance at field condition. Evaluation of the actual performance of sprinkler irrigation is very important to know the general status of existing system, and for identifying the gaps and applying mitigation measures. The Arjo-Didessa sugar factory is producing sugarcane for about two decades. Sugar cane fields at study area were irrigated irrespective of the soil type, growing month and stage of crop growth with the design application efficiency of 75%. But, now the system is not working with the full design capacity. In irrigation field under and over watering, plant showing yellow color and wilt are observed. However the actual performance of the existing sprinkler system was not clearly understood so far and evaluated yet; so that evaluating the actual sprinkler performance under existing condition was very important. Therefore, this study was conducted to assess the existing sprinkler irrigation performance by measuring the performance indicators of the irrigation as it is normally practiced. This study was started from field observation and referring design document of focus area. Primary and secondary data were used to attain the objective of the study. The soil physical characteristics and the gravimetric water content were determined in the laboratory using collected soil samples from the field. CROPWAT 8.0 model was used to estimate the CWR and effective rainfall (Pe). During the study, 12 field experiments were conducted at two irrigation command areas for hydrant pressure of 3.5 and 4.0 bars, to check infield water application uniformity, for both overlapping and single sprinkler test by installing catch can in grid spacing of 3*3m with three replications. The result shows, measured irrigation interval and sprinkler set hour was vary through growing month and stage. Average sprinkler discharge is 0.295 lit/sec which is below design capacity of 0.54 liter/sec. The mean application rates for 18m x18m sprinkler spacing were 3.27mm/hr. The CU of 72% and 79% obtained at the hydrant pressure of 3.5 and 4.0 respectively. Also DU values obtained from catch can tests data are 62.5% and 69% at respective hydrant pressure, which indicates at poor range and lower than of minimum acceptable range. The values of the system CU and system DU are very closely to the calculated CU and DU values. The catch can data for single sprinkler were overlapped for different spacing‟s. Acceptable value of CU equal to 78% and 81%; and DU of 72% and 77% at operating pressure 3.5 bar and 4.0 bar respectively obtained at 12m x 18m spacing. The PAE of 74.5% and 80%; and PAELQ of 46.5% and 55.5% were obtained at 3.5 and 4.0bar respectively. The obtained results of the lower quarter adequacy (ADlq) were 0.72 and 0.86 for operating hydrant pressure of 3.5 and 4.0 bar respectively. The current estimated average AEa was 59.5%. Generally, the result of this study shows, the existing system performance is poor. The system has to be improved and revised. So that, the irrigation scheduling based on the actual efficiency was recommended with respect of growing month and stage of growth. The project should use the best combination of the hydrant operating pressure and set time to be successful and work as planned