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Internal renewable water resources (IRWR) in Sudan are rather limited. The erratic nature of the rainfall and its concentration in a short season places Sudan in a vulnerable situation, especially in rainfed areas. Surface water in Sudan mainly comprises the Nile river system (nilotic water) and a few other, non-nilotic streams. About 43 percent of the Nile basin lies within Sudan, while 72 percent of Sudan lies in the Nile basin.
Sudan shares parts of the following basins with neighbouring countries:
- Nile basin, covering 1 350 616 km² of the country (72 percent of the area of the country)
- Northern Interior basins, covering 310 888 km² in the northwest part of the country (16.5 percent)
- Lake Chad basin, in the west of the country along the border with Chad and the Central African Republic, covering 101 048 km² (5.4 percent)
- Northeast Coast basins, representing a strip along the Red Sea coast of the country, covering 83 840 km² (4.5 percent)
- Baraka basin, along the Eritrean border, covering 24 141 km² (1.3 percent)
- Mareb-Gash basin, also along the Eritrean border, covering 8 825 km² (0.5 percent) (FAO, 1997; UNEP, 2007)
The last two, Mareb-Gash and Baraka, are seasonal streams, also named khors.
The Nile system within Sudan comprises:
- The Blue Nile and Atbara rivers originating in the Ethiopian highlands
- The White Nile system, downstream of Malakal, originating on the Great Lakes Plateau
- A small part of the Bahr El Ghazal basin, an internal basin in southwest Sudan and mainly located in South Sudan.
The characteristics of the Nile system tributaries are the following:
- The Blue Nile: The flow of the Blue Nile reflects the seasonality of rainfall over the Ethiopian highlands where the two flow periods are distinct. The flood period or wet season extends from July to October, with the maximum in August-September, and low flow or dry season from November to June. Therefore the annual Blue Nile hydrograph has a constant bell-shaped pattern, regardless of variation in the annual flow volumes. The average annual inflow flow of the Blue Nile and its tributaries from Ethiopia to Sudan is estimated at 52 600 million m³. The daily flow fluctuates between 10 million m³ in April to 500 million m³ in August (ratio of 1:50).
- The White Nile: The average annual flow of the White Nile System entering Sudan from South Sudan is about 34 000 million m³. During the flood period the Blue Nile forms a natural dam that obstructs the flow of the White Nile and consequently floods the area upstream of the confluence.
- The Atbara river: This is a highly seasonal river, with an annual flow entering Sudan from Ethiopia of 4 370 million m³ restricted to the flood period of July-October, the maximum occurring between August-September. The river has a steep slope and small catchments, and reflects the rainfall over the upper catchments as runoff at Sudan border within one to two days.
- The Setit-Tekeze river: This also is a highly seasonal river, with an annual flow crossing the border from Ethiopia to Sudan of 7 630 million m³/year, restricted to the flood period of July-October with the maximum occurring between August-September. Originating in Ethiopia, the river becomes the border between Ethiopia and Eritrea before entering Sudan.
- The Main Nile: The reach of the Nile downstream of the confluence of the Blue Nile and the White Nile rivers is known as the Main Nile. The Atbara river is regarded as the only and last tributary joining the Main Nile. The average annual flow of the Main Nile at the Sudan-Egypt border at Aswan (leaving Sudan), upstream of the reservoir is estimated at 84 000 million m³. This is less than the sum of IRWR and the above water resources flowing into Sudan due to evaporation (see below).
The major non-nilotic streams are the Mareb-Gash and Baraka in the east of the country, coming from Eritrea, both of which are characterized by large variations in annual flow and heavy silt loads. Average annual flow is estimated at 700 million m³. The major groundwater formation and basin is the Nubian Sandstone Basin covering a total area of 2.2 million km². It is the largest volume of freshwater in the world with an estimated 150 000 000 million m³, mostly non-renewable (fossil water), except for the Nubian Nile aquifer recharging from the Nile river. This deep artesian aquifer underlies approximately 376 000 km² of Sudan, where it is almost untapped as in Chad, but contrarily to Libya and Egypt where it is tapped (UNEP, 2007). The groundwater outflow from Sudan to the Nubian aquifer in Egypt is estimated at 1 000 million m³/year. A small portion of the Umm Rwaba aquifer lies also in Sudan.
In 2013, three wetlands are Ramsar listed, covering around 2.5 million ha: the Dinder National Park in Sennar State, and the Dongonab Bay (Marsa Waiai) and the Suakin (Gulf of Agig) in the Red Sea State.
Sudan’s IRWR are estimated at 4 000 million m³/year (Table 2). Total inflow is estimated at 99 300 million m³/year, of which 98 600 million m³/year through the Nile system (see bullet points a-d above) and 700 million m³/year from Eritrea. Therefore total natural renewable water resources are equal to 103 300 million m³/year. Natural surface water outflow to Egypt is 84 000 million m³/year. This is less than the IRWR plus inflow, since 19 300 million m³/year is estimated to evaporate in the swamps in the south of the country. Accounted water resources are less due to an agreement between pre-2011 Sudan and Egypt that 65 500 million m³/year should enter Egypt from Sudan, leaving 18 500 million m³/year for pre-2011 Sudan (=84 000-65 500). While it is not known yet what the treaty will be after the splitting of Sudan into South Sudan and Sudan, this will have consequences for both South Sudan and Sudan. For now AQUASTAT has considered that the outflow secured through treaties to Egypt is still 65 500 million m³/year and that 26 500 million m³/year of the total flow of 34 000 million m³/year flowing from South Sudan to Sudan is submitted and secured through the agreement (from South Sudan to Sudan and then from Sudan to Egypt). These 26 500 million m³/year are equal to 34 000x(65 500/84 000), whereby 65 500 million m³/year is the inflow into Egypt according to the agreement and 84 000 million m³/year is the flow to Egypt (see above). Considering the outflow of 65 500 million m³/year as per the agreement, total (accounted) renewable water resources are equal to 37 800 million m³/year (103 300-65 500). It should be mentioned that this calculation done by AQUASTAT is an interim calculation that neither represents AQUASTAT’s position or recommendation, nor should it carry any political significance. Information will be updated as soon as information on a new or updated treaty will become available.
The high variability of river flows necessitates storage facilities. The total storage capacity of the following five main dams is estimated at 21 230 million m³, reduced to about 19 170 million m³ owing to sedimentation and debris:
- The Sennar dam on the Blue Nile (design capacity 930 million m³, present capacity 370 million m³) is for the flood control and irrigation of the Gezira Scheme.
- The Roseires dam on the Blue Nile (design capacity 3 000 million m³, present capacity 2 200 million m³; there are plans to increase the present dam height of 60 m to provide an extra capacity of 4 000 million m³) is for flood control and utilizes part of the country’s share of the Nile waters for irrigation.
- The Jebel Aulia dam on the White Nile (design capacity 3 500 million m³, present capacity is similar) was originally designed to benefit Egypt by augmenting the supply of summer flow to the Aswan dam. After the construction of the High Aswan dam it was no longer needed by Egypt and was officially handed over to the Sudan in 1977.
- The El Girba dam on the Atbara River (design capacity 1 300 million m³, present capacity 600 million m³) is for flood control, irrigation of New Halfa Scheme for the benefit of the people displaced by the High Aswan dam, and hydropower.
- The Merowe dam on the 4th cataract of the Nile, completed in 2009, created a reservoir of 12 500 million m³ and 174 km long and has a hydropower capacity of 1 250 MW.
A small barrage was constructed on the Rahad river to divert floodwater to the Rahad Agricultural Scheme and to siphon underneath the Dinder river to augment the water supply during the dry season from the Meina Pump Station on the Blue Nile.
Four additional dams are proposed in Sudan at different proposal stages:
- The Kajbar dam planned upstream Lake Nubia, also called Lake Nasser on the Egyptian side, on the 3rd cataract of the Nile, close to the Egyptian border, was granted US$705 million and 5-years contract in 2010 by the government for its construction: it will generate 360 MW for a reservoir with a surface area of 110 km².
- The Dal dam on the 2nd cataract would have a height of 25-45 m and a capacity of 340-450 MW.
- The Shereik dam on the 5th cataract of the Nile.
- The Upper Atbara Project, an irrigation and hydropower complex in eastern Sudan, was awarded a US$838 million contract in 2010.
Non-conventional sources of water are limited in Sudan. However, the desalination of seawater was introduced recently in Port Sudan town. Fossil groundwater resources are estimated to be 16 000 000 million m³.