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The Nile basin constitutes about 98 percent of the total area of the country, while a fringe of 5 849 km² along the country’s border with Kenya belongs to the Rift Valley basin. About 8 percent of the Nile basin lies within Uganda (NBI, 2012).
The Ugandan part of the Nile basin shares a large part of the extensive interconnected system of the Equatorial lakes that forms the upper part of the White Nile. Lake Victoria, which drains a total area of about 184 000 km² in Rwanda, Burundi, the United Republic of Tanzania, Kenya and the entire southern part of Uganda, has its outlet at Jinja. Passing the Owen Falls Dam, the water flows through the Victoria Nile into Lake Kyoga and subsequently into the northern end of Lake Albert. The other branch of the Lake system, i.e. Lake George and Lake Edward, is connected via the Semliki river, which flows into the southern end of Lake Albert. From Lake Albert, the Albert Nile flows northwards towards South Sudan.
The Ugandan Nile basin is divided into eight sub-basins, which are relatively small contributors to the Nile flow, but their yields dominate the water resources potential within Uganda. While the Nile and its flow characteristics are important from both an international and national point of view, the Ugandan catchments are important from a district and local point of view. The eight sub-basins are detailed in Table 3.
Productive aquifers are mainly found in the weathered bedrock layer overlying the crystalline basement rock, and in faults and fractures in the basement. In mountain areas, however, aquifers occur in volcanic formations and groundwater occurrence is often in the form of springs. Ongoing studies are still carried out to map out ground water resources in the country.
Uganda’s wetlands are widespread and hydrologically connected to rivers and lakes. In 2008, almost 11 percent of the country, or 26 308 km², was covered by wetlands (swamps), of which about one fifth is permanently flooded (NEMA, 2010). In the south and west of the country, they form an extensive low gradient drainage system in steep V-shaped valley bottoms with a permanent wetland core and relatively narrow seasonal wetland edges. In the north, they mainly consist of broad flood plains. In the east, they exist as a network of small, vegetated valley bottoms in a slightly undulating landscape. The most common wetlands are papyrus, reed and grass swamps. Vegetation in wetlands ranges from floating plants, short or tall grasses, reeds, sedges, shrubs to trees. There are 12 Ramsar sites in 2013, covering 454 303 ha, which is equal to 17 percent of all wetland areas in Uganda.
Internal renewable surface water resources are estimated to be 39 km³/year while renewable groundwater resources are believed to be around 29 km³/year, but all of this is considered to be overlap between surface water and groundwater, keeping the total IRWR at 39 km³/year (Table 4). External water resources of 21.1 km³/year comprise inflow from Lake Victoria, of which 10.7 km³/year from United Republic of Tanzania and 8.4 km³/year from Kenya, as well as 2 km³/year inflow via Lake Edward and Lake Albert from the Democratic Republic of Congo. The dependency ratio is thus around 35 percent and the total renewable water resources are 60.1 km³/year, or 1 599 m³/year per capita in 2013. The ouflow of surface water leaving the country through the White Nile in South Sudan is estimated at 37 km³/year.
The major lakes in Uganda are given in Table 5. Adding the over 160 minor water bodies gives a total inland water area covering 41 740 km², which is equal to 17 percent of the country area. There are also over 1 000 dams and valley tanks for both aquaculture and livestock watering. Their cumulative storage capacity is 27.5 million m³ in 2013 (MWE, 2013b), including the Ongom and Owameri dams deserving the Ongom irrigation scheme, and with a capacity of 0.25 million m³ and 0.125 million m³ respectively (MAAIF, 2013). The Government carries out regular programmes to construct additional dams and valley tanks and to increase the water capacity for agricultural production (Republic of Uganda, 2010).
The Owen Falls Dam is located at the outlet of Lake Victoria. Lake Victoria is a natural lake, but it is considered that due to the Owen Falls Dam there is an additional capacity of 200 km³. Also considering that 50 percent of the total surface area of Lake Victoria is located in the United Republic of Tanzania, 40 percent in Uganda and 10 percent in Kenya, the part of the reservoir capacity considered in Uganda is 40 percent of the total of 200 km³, or 80 km³. Completed in 1954, it serves the Nalubaale hydropower plan which had an installed hydropower capacity of 180 MW, extended later by 90 MW with the Kiira hydropower plant. The 250 MW Bujagali hydropower plant near Jinja, about 8 km north of Lake Victoria, and completed in 2012, has a reservoir capacity of 54 million m³. The 600 MW Karuma hydropower plant is under construction on the Victoria Nile and will be the largest in the country once completed. Other projected schemes located along the Nile include Ayago (240/300 MW), Arianga (400MW) and Isimba (180MW). There are also various mini hydropower plants, already completed, under construction or in projects.