GIS-based land suitability assessment for surface irrigation: a case of Gilgel Gibe watershed, Jimma Zone, Ethiopia

Systematic assessment of available water and potential land surface suitable for irrigation at watershed level is essential for the planning and decision-making of new irrigation development projects. Hence, the intended aim of this research is to assess the land suitable for surface irrigation and available surface water in Gilgel Gibe watershed using Geographical Information System (GIS) and Remote Sensing (RS) technique. The surface water availability was evaluated by developing flow duration curve (FDC) and analyzing 90% available flow of Gilgel Gibe River. The land surface suitability was determined through GIS-based multi-criteria evaluation (MCE) technique, which considers the interaction of major land suitability factors such as slope, river proximity, soil type, and land use land cover. The factors were weighted using a pair-wise comparison matrix to evaluate the importance of one factor over the other, for physical land suitability. The result indicated that about 2.64, 14.61, and 58.27% of the catchment were found to be highly, moderately, and marginally suitable, respectively, and the remaining 24.48% was found to be not suitable in terms of physical land suitability. In terms of water availability, the flow duration curve (FDC) result indicated that the 90% available flow throughout the year of Gigel Gibe River is 9.13 m3/s. Hence, in the month of December, the river has a capacity of irrigating only 5.79% of total irrigable land, while in the months of May to September, the river has a capacity of irrigating the whole irrigable land. The low flow of the river has a potential of irrigating large area in wet season and less area in dry season. Hence, water storage structures are needed to irrigate the whole potential irrigable land during dry season.