GIS-Based Irrigation Potential Assessment for Surface Irrigation: The Case of Birbir River Watershed, Oromia, Ethiopia

The assessment process of surface irrigation has to integrate information about the suitability of the land; water resource availability and water requirements of irrigate able areas in time and place. Birbir River is one of well-known river found in western Ethiopia. The Birbir River is a tributary of the Baro-Akobo river basin, which creates Baro River when it joins with Gebba River. Ethiopia has immense potential in expanding irrigation using available water resources. But due to lack of information related to cultivable and irrigation suitability of the land, its agricultural system does not yet fully productive. Geographic Information System can be an effective tool in identifying irrigable land and mapping of suitable land for irrigation. Therefore, the objective of the present study was to assess the surface irrigation potential of the Birbir river watershed using ArcGIS 10.3. Different methods of data processing and analysis have been employed in this study. The main suitability factors used to identify the potential irrigable land for surface irrigation were slope, soil texture, soil depth, soil type, soil drainage characteristics, land use, land cover and distance to water source. The consistency of rainfall and stream flow data were checked by double mass curve and the areal mean of rainfall and temperature data were determined by using Theissen polygon method whereas the irrigation water demands of the selected two crops (maize and potato) were calculated separately using FAO cropwat model. By weighting values of the seven factors using Analytic Hierarchy Process and overlaying by weighted overlay in ArcGIS 10.3, the irrigation suitability map was developed and potential irrigable land for surface irrigation was found to be 17%, 63% and 20% for highly suitable (S1), moderately suitable (S2), and marginally suitable (S3) respectively. Irrigation potential of the Birbir river watershed was obtained by comparing monthly gross irrigation requirements of the identified land suitable for surface irrigation and the available 80% mean monthly dependable flows in the river catchments. The potential irrigable land that can be irrigated without provision of storage structures was found to be around 68,000 ha from the total of 106,223 ha suitable land for surface irrigation.