GIS-BASED SURFACE IRRIGATION POTENTIAL ASSESSMENT OF MEKI RIVER WATERSHED, CENTRAL RIFT VALLEY OF ETHIOPIA

Abstract

Irrigation can contribute to food security by increasing food availability and cash income of smallholder farmers. However, surface irrigation development in the study area is hindered due to lack of reliable data of suitable land and available water potential. Therefore, this study assessed the land and water resources of Meki River watershed in rift valley lakes basin in Ethiopia using Geographic information system to identify suitable land and available water potential for surface irrigation. Land suitability factors such as soil depth, soil texture, soil drainage, slope and land use/cover were considered and their suitability analyzed using ArcGis10.3. Water availability assessed using soil and water assessment tool and calibrated and validated with observed flow. Flow duration curve from monthly simulated flow was developed to obtain the reliable monthly flow at 80% probability. Irrigation water requirements estimated using CROPWAT8.0 for the Maize, Onion and Tomato and compared with dependable flow to compute the potential irrigable area. Regarding evaluation factors the results showed that 52.31 % of slope, 89.9% % of soil depth, 75.95% of soil drainage 99.65% of soil texture and 94.73 % of land use land cover were in the range of highly to marginally suitable, whereas 47.69 % of slope, 10.1% of soil depth, 24.1% of soil drainage, 0.35% of soil texture and 5.27 % of land use land cover restricted for surface irrigation. Further weighted overlay results showed that 177,199 ha were in the range of highly to marginally suitable whereas 35798 ha were unsuitable. Besides, the results revealed that maximum and minimum dependable flow during crop growing period were 39.6 m 3 /s and 0.05 m 3 /s respectively. Moreover, the results showed that irrigation water demands vary from crop to crop, and 4126.04 ha were obtained to be potentially suitable for the development of surface irrigation project. This study concludes that there is huge suitable land and insufficient water availability in the watershed. Therefore, irrigation potential of the watershed can be increased through using water saving technology such as drip, sprinkler and selecting other less sensitive crops, also using other water sources such as Lake Water, ground water and rain water harvesting