The Eastern Nile (EN) Basin (Figure 1) constitutes over 60% of the total area of the Nile River Basin and contributes about 86% of the average annual flow of the main Nile River estimated at 84 Bm3 at the Aswan High Dam High Aswan Dam in southern Egypt. It is one of the important basins in Africa that supports and extraordinary range of ecosystems ranging from high mountain forests, savanna woodlands, extensive wetlands and arid deserts. A summary of the main characteristics of the Eastern Nile Sub-basins is outlined in Table1 (ENTRO, 2012).
Many studies indicate that pressure on water resources in the Eastern Nile Basin is likely to increase dramatically in the near future as a result of high population growth and increasing development related water needs in all the riparian states. However, in spite of the national and international importance of this basin, relatively few detailed studies have been conducted and there is only a limited understanding of the basin’s detailed climatic, hydrologic, hydro-geologic and hydraulic characteristics (Awulachew et al, 2008) .Unless the above characteristics are properly understood at the sub-basin levels, adequate planning, development and management of the overall basin cannot be achieved.. Therefore there is a need for the development of a water balance and accounting model for the Easter Nile at sub-basin level. The model should include the water supply and demand for major productive activities (existing and proposed) at present and future and should help in the assessment of downstream implications of proposed development project. The water balance model could be a useful tool in the optimization of supply through identifying potential areas for water harvesting and management of groundwater recharge, and also in the water demand management particularly in areas characterized by low water use efficiency. This ensures optimal and beneficial use of water resources in the basin for the socioeconomic well being of the population.