Blue Nile
Blue Nile Falls (Tis Issat) at Lake Tana
Origin	Lesser Abay/Lake Tana
Length	1,450 km (900 mi)
Avg. discharge	2,349 m3/s (83,000 cu ft/s)
Basin area	325,000 km2 (125,000 sq mi)

Map of the Blue Nile

Confluence of Blue and White Nile near Khartoum

The Blue Nile (Amharic: ዓባይ^?; transliterated: ʿAbbay but pronounced Abbai, Arabic: النيل الأزرق‎ an-Nīl al-Azraq) is a river originating at Lake Tana in Ethiopia. With the White Nile, the river is one of the two major tributaries of the Nile. The upper reaches of the river is called the Abbay in Ethiopia, where it is considered holy by many, and is believed to be the River Gihon mentioned as flowing out of the Garden of Eden in Genesis 2.^[1]

Course[edit]

According to materials published by the Ethiopian Central Statistical Agency, the Blue Nile has a total length of 1,450 kilometres (900 mi), of which 800 km (500 mi) are inside Ethiopia.^[2] The Blue Nile flows generally south from Lake Tana and then west across Ethiopia and northwest into Sudan. Within 30 kilometres (19 mi) of its source at Lake Tana, the river enters a canyon about 400 kilometres (250 mi) long. This gorge is a tremendous obstacle for travel and communication from the north half of Ethiopia to the southern half. The power of the Blue Nile may best be appreciated at Tis Issat Falls, which are 45 metres (148 ft) high, located about 40 kilometres (25 mi) downstream of Lake Tana.

Although there are several feeder streams that flow into Lake Tana, the sacred source of the river is generally considered to be a small spring at Gish Abbai,situated at an altitude of approximately 2,744 metres (9,003 ft). This stream, known as the Lesser Abay, flows north into Lake Tana. Other affluents of this lake include, in clockwise order from Gorgora, the Magech, the Northern Gumara, the Reb, the Southern Gumara and the Kilte.^[3] Lake Tana's outflow then flows some 30 kilometres before plunging over the Tis Issat Falls. The river then loops across northwest Ethiopia through a series of deep valleys and canyons into Sudan, by which point it is only known as the Blue Nile.

There are numerous tributaries of the Abay between Lake Tana and the Sudanese border. Those on its left bank, in downstream order, include the Wanqa River, the Bashilo River, the Walaqa River, the Wanchet River, the Jamma River, the Muger River, the Guder River, the Agwel River, the Nedi River, the Didessa River and the Dabus River. Those on the right side, also in downstream order, include the Handassa, Tul, Abaya, Sade, Tammi, Cha, Shita, Suha, Muga, Gulla River, Temcha, Bachat, Katlan, Jiba, Chamoga, Weter and the Beles.^[3]

After flowing past Er Roseires inside Sudan, and receiving the Dinder on its right bank at Dinder, the Blue Nile joins the White Nile at Khartoum and, as the River Nile, flows through Egypt to the Mediterranean Sea at Alexandria. The Blue Nile is so-called because during flood times the water current is so high, it changes colour to an almost black; since in the local Sudanese language the word for black is also used for the colour blue.

The distance from its source to its confluence is variously reported as 1,460 and 1,600 kilometres (907 and 1,000 miles). The uncertainty over its length might partially result from the fact that it flows through a virtually impenetrable gorges cut in the Ethiopian Highlands to a depth of some 1,500 metres (4,900 ft)—a depth comparable to that of the Grand Canyon of the Colorado River in the United States.

Water flow[edit]

The flow of the Blue Nile reaches maximum volume in the rainy season (from June to September), when it supplies about two thirds of the water of the Nile proper. The Blue Nile, along with that of the Atbara River to the north, which also flows out of the Ethiopian Highlands, were responsible for the annual Nile floods that contributed to the fertility of the Nile Valley and the consequent rise of ancient Egyptian civilization and Egyptian Mythology. With the completion in 1970 of the Aswan High Dam in Egypt, the Nile floods ended.

The Blue Nile is vital to the livelihood of Egypt. The Blue Nile, the most significant tributary of the Nile, contributes more than half of the Nile's streamflow.^[4] Though shorter than the White Nile, 59% of the water that reaches Egypt originates from the Blue Nile branch of the great river; when combined with the Atbara River, which also has its source in the Ethiopian Highlands, the figure rises to 90% of the water and 96% of transported sediment. The river is also an important resource for Sudan, where the Roseires and Sennar dams produce 80% of the country's power. These dams also help irrigate the Gezira Plain, which is most famous for its high quality cotton. The region also produces wheat and animal feed crops.

The Nile River, the longest river in the world,^[5] is an "international" river as its water resources is shared by ten countries, namely, Tanzania, Uganda, Rwanda, Burundi, Democratic Republic of the Congo, Kenya, Ethiopia, Eritrea, Sudan and the Arab Republic of Egypt. In particular, the Nile River provides the primary water resource and so it is the life artery for its downstream countries such as Egypt and Sudan.

Several attempts have been made to establish agreements between the countries sharing the Nile waters. It is very difficult to have all these countries agree with each other given the self-interest of each country and their political, strategic, and social differences. On 14^th of May 2010 (at Entebbe, Uganda), Ethiopia, Rwanda, Tanzania and Uganda signed a new agreement on sharing the Nile water even though this agreement raised strong opposition from Egypt and Sudan. Ideally, such international agreements should promote equitable and efficient usage of the Nile basin's water resources. Without a better understanding about the availability of the future water resources of the Nile River, we could expect more conflicts between these countries relying on the Nile for their water supply, economic and social developments.^[4]

In November 2012, Ethiopia began a six-year project for the construction of a 6,000 megawatt hydroelectric dam on the river. Despite the dam being a huge boost for the Ethiopian economy, Sudanese and Egyptian contingents voiced their concern over a potential reduction in water available to them.^[6]