Geographical Information System-Based Surface Irrigation Potential Assessment: A Case of Geba River Watershed, Oromiya, Ethiopia

Abstract

Proper land suitability evaluation of land resources in irrigation command area is a prerequisite for better utilization of land resources which helps to optimize and sustain the productivity of these land resources. However, in the Geba Watershed, there is no study available on the assessment of irrigation potential. Hence, this study is aimed to assess the surface irrigation potential of the Geba River Watershed in the Ilubabor Zone of Oromiya Regional State through Geographical Information System (GIS) techniques. Watershed delineation, identification of potentially irrigable land, estimation of irrigation water requirement, and surface water resources of the river were the steps followed to assess this irrigation potential. To identify potentially irrigable land, irrigation suitability factors such as soil, slope, land cover/use, distance from water supply (sources), and distance from the road were taken into account. Irrigation suitability factors are classified based on the Food and Agricultural Organization Guideline for land evaluation. The suitability of each factor was first analyzed individually and finally weighted using Analytical Hierarchy Process (AHP) method from the pair-wise comparison matrix to obtain potentially irrigable land. The irrigation suitability analysis of these factors indicate that 50.21% of slope,50.47% of LULC,65.07% of the distance from the water source, and 52.46% of the distance from the road of the study area are in the range of highly suitable to marginally suitable for surface irrigation and 77.39% of the soil in the study area is in the range of highly suitable to moderately suitable. By weighing analysis of all factors about 88.07 % of the study area was found in a range highly suitable to marginally suitable whereas about 11.93 % was restricted for surface irrigation developments. To grow on these identified irrigable areas, three crops such as potato, tomato, and cabbage are selected and their gross irrigation demand was computed from climate input data using CROPWAT 8.0 software. The low flow (90% time of exceedance flow of Geba River) was estimated by the flow duration curve. By comparing the required water and available monthly low flow of the Geba River, the river had insufficient capacity for irrigation application of the command area. Therefore, construction of storage structures or using ground water can be an option to meet irrigation potential