Irrigation is an important investment for improving rural income through increased agricultural production. The expansion of irrigation and effectively manage agricultural water holds significant potential to enhance productivity and reduce vulnerability to the climactic volatility in any country. Investigation of available water resources and potentially irrigable land is essential for the development of irrigated agriculture. This study was concerned with the assessment of surface irrigation potential availability in the Gilgel Abay watershed by implementing Arc GIS 10.1. Assessment of land suitability for irrigation is essential for the long production of crops and food security of the ever-growing population, as well as for the efficient use of limited physical land resources in the studied area. This research focuses on the possibilities for catchment surface irrigation and a water-saving sowing time scenario. The physical and chemical properties of the soil, slope, LULC, distance from water sources (Proximity to water), and surface water resource availability were all considered while determining land suitability for surface irrigation. According to the results of the land suitability evaluation ratings based on quantitative and qualitative land suitability for surface irrigation, 22.59 percent (86,747.19 ha) of lands in the research region were in the high to marginally suitable classes, while 77.41 percent were in the non-suitable class (297,252.4 ha). For November, December, January, and February sowing time scenarios, total irrigation water demand is 5,927.5Mm3, 370.2 Mm3, 455.4 Mm3, and 506.2 Mm3 respectively accordingly to irrigate 86961.24ha of irrigable land for 10 selected and dominating crops. The most favorable sowing starting month, according to sowing time scenarios, is in December, in order to save water or use less water to irrigate all available irrigable land and to fulfill all selected and dominating crops in the research area. Therefore, as a result, this research will assist all participants in making irrigation investment decisions and identifying long-term irrigation investment prospects in the study area.