“GIS Based Surface Irrigation Suitability Analysis of Birr River Catchment, Abbay Basin, Ethiopia”

Abstract

Although Ethiopia has a large potential to develop irrigation, only 7.84% of the 3.7 million hectares of land potentially available has been developed. To examine the underlying causes, this study evaluates the suitability of surface water irrigation in Birr River catchment. Birr River catchment is located at the South west Gojjam part of the Abay River Basin. The study area covers an area of about 3191 square kilometers. The investigation of available land and water resources for irrigation is important for planning their use. This study was initiated with the objective of analyzing the water and land resources potential of river catchments in this River basin for irrigation development and generating geo-referenced map of these resources by using Geographic Information System. Watershed delineation, identification of potential irrigable land, estimation of irrigation water requirement and surface water resources of river catchments were the steps followed to analyze this irrigation potential. The investigation includes data like topography, climate, soil, land use pattern, water availability and agricultural practices. Furthermore the irrigation suitability criteria were defined based on these variables and weighted using pairwise comparison technique. With the purpose to evaluate units for irrigation suitability stream networks were characterized and soil types as well as land use were mapped. Crop development with respect to the prevailing conditions is integrated within this situation. Integrating all the aggregate suitability variables, the potential capacity of irrigable land was identified and mapped as well. The result indicates that nearly 36.54% of the River catchment is suitable for surface irrigation. However, by analyzing 20 years of river discharge, less than 1.3% of the potential irrigable area (or less than 0.47% of the River catchment area) could be irrigated consistently by run-off-the river-systems in the driest period which is March. Other months which are recommended as irrigation period have greater potential than month March. Thus, the irrigation potential in the Birr River catchment can only be met by increasing dry season flows (if proven feasible) and by supplying water from future reservoirs or by using water from underground. The capacity of low flow as well as 80% and 90% time of exceedance flow of the available surface water in the respective sub watersheds was also estimated. The area that can be irrigated with this flow was computed for the selected cropping pattern which is Maize. The discharges at un-gauged sites were estimated from gauged sites by applying regionalization method using SWAT model and results were obtained on monthly bases. Hence, the minimum simulated stream flow at the outlet of drainage basin was 1.69m3 /s occurred on the month of March.