EVALUATION OF SMALL SCALE IRRIGATION SYSTEM IN WESHA SOYAMA VILLAGE IN SIDAMA REGIONAL STATE

Abstract

Field assessment to evaluate water use efficiency of small-scale irrigation projects plays a vital role in improving the existing projects and assist engineers in designing new systems so that irrigation practice becomes sustainable. Therefore, this study was carried out to evaluate the performance of Wesha SSIS using internal and external performance indicators. This study used primary and secondary data for assessing the irrigation performance. The primary data collected includes field observation, soil samples to characterize the soil in terms of physical characteristics and discharge measurement at main and field canals. Secondary data collected were total yield, area irrigated, crop type, and climate data. CROPWAT 8.0 model was used to calculate ETo and the crop water requirement. The analysis of internal performance indicators showed that the conveyance, application, storage efficiencies, distribution uniformity, and overall irrigation efficiencies were calculated and the results were 66.43, 46.70, 96.02, 91.88 and 31.02% respectively. Since the overall scheme efficiency at the study area was 31.02%, which was very poor; which mean that irrigation water loss was very large indicating need for scheme improvement. The analysis of water related indicators such as RWS and RIS were found to be 1.35 and 1.14 respectively. Since the value of RWS and RIS is greater than one this implies that, there were sufficient relative irrigation supply and high relative water supply which was beyond the crop demand. This shows that it could irrigate additional farm land with this delivery amount and available effective rainfall in the study area. The value for WDC at the study area was found 1.08 this implies that, the river diversion infrastructure is capable of delivering the necessary peak water demand. Agricultural related indicators such as, the output per unit command area is 38,939.2 Birr/ha and output per unit irrigated area is 139,068.6 birr/ha. Water productivity indicators such as, Output per unit water consumed and Output per unit irrigation water supplied are 45.24 birr/m3 and 0.15 birr/m3 in Wesha SSIS respectively. Based on the results obtained can be concluded that the agriculture production indicators are found to be reasonable. The potential evapotranspiration of the study area, calculated using CROPWAT Model, is more than the effective rainfall in most of the months calling for supplemental irrigation. The effective rainfall is more than ETo by 10.96 mm/month during July; meaning that no irrigation is required during this month. Therefore, those farmers who grow crops on July are less likely to apply supplemental irrigation. On the other hand, extensive irrigation is essential for crops planted particularly on October, November, December, January, February, March, April, May (with 84.67, 96.9, 100.16, 82.86, 93.2, 85.15, 88.07 and 53.95 mm of irrigation water requirements, respectively). During the study period, on-site soil erosion, temporary water logging and illegal canal breaching are the observed major problems associated with the farmers’ irrigation practices. Weak operation and maintenance of the project is also witnessed. Since the current irrigable area is below the irrigable area at the initial period of the irrigation scheme, thus the project is not sustainable; due to the fact that SIA is much far from 100%. Settlement expansion is the major reason observed in the field as threat to the sustainability of the project