Evaluation of irrigation potential and irrigation water supply systems efficiency: A case study in Wonchi district, south west Shoa zone, Oromia region, Ethiopia.

Abstract

Evaluation of irrigation potential and irrigation water supply systems efficiency is crucial especially for areas like wonchi district; where the issue of irrigation potential assessment was not addressed; and high irrigation water loss was observed; but not quantified yet. To address these issues irrigation potential was evaluated in terms of surface water and land resources potential. While irrigation water supply systems efficiency was evaluated in terms of unlined and lined canals conveyance efficiency and water losses. Surface water potential was determined based on rivers discharge measurement using area velocity method and irrigation water supply potential was determined from surface water resource potential, based on irrigation and major crop growth stage period.Suitable land of the study area was determined from land resource irrigation suitability analysis using GIS spatial analysis tools. Conveyance efficiency and water losses of unlined and lined canals were determined using inflow and out flow method, based on canal discharge measurements. Accordingly, the total surface water potential of wonchi district was determined to be about 406.22 Mm3 per year. The total irrigation water supply potential, used for irrigation during dry season was determined to be only about 7.964 Mm. 3 (2%) of the district surface water potential. This supply potential can satisfy irrigation water demand of only about 3360 ha land area. However, 14763 ha, land area was determined to be suitable for irrigation. To satisfy this land area, irrigation water demand, about 34.996 Mm3 irrigation water was required. These supply and demand result comparison showed that the ratio was 19 % to 81% respectively. Similarly, irrigation water supply systems efficiency evaluated result revealed that conveyance efficiency of unlined canal was determined to be 55.88% and that of lined canal was 91.96%.From these results it was concluded that lining reduced water losses by 36.08% .Irrigation water supply potential is the limiting factor as compared to determined suitable land for irrigation in won chi district. So, there is need to increase irrigation water supply potential during dry season by collecting the rivers run off during the wet season. Lining distributary canals also need major focus to increase irrigation water supply potential and utilize suitable land resource for irrigation.