The Blue Nile is one of two rivers that meet at Khartoum, Sudan, to form the Nile River. The other river, the White Nile, attracts more attention because it flows from Lake Victoria and points even further south, giving the Nile river system much of its official length. The Blue Nile, in contrast, passes through only two countries (Ethiopia and Sudan) in its distinctly shorter, winding course to Khartoum. In its historical relevance, however, the Blue Nile is the more important tributary of the two. It is the source of the annual flooding that was so important to ancient Egyptian civilization.
The Blue Nile flows out of Lake Tana in the midst of the highlands of Ethiopia. These highlands are comprised of volcanic rock which yields fertile sediments when eroded by rain. There is plenty of the latter, above all in the summer: the same monsoon system that brings the famous heavy rains to India passes first over Ethiopia in its journey along the rim of the Indian Ocean.
Between June and September, the Blue Nile swells with the monsoon runoff, carrying heavy quantities of sediment on its course to Khartoum. The rush of water is so heavy that it often causes the flow of the White Nile to stop by the force of its own water pressure. Until the construction of the Aswan High Dam, and the resulting creation of Lake Nasser in southern Egypt, this heavy flow proceeded to flood the entire Nile Valley, depositing its rich layer of silt to fuel agriculture for another year.
Egypt is often said to be the gift of the Nile. Much of the truth of this statement is directly attributable to the contribution of the Blue Nile. Not only did the Blue Nile furnish Egypt with the silt that ensured its agricultural fertility, but it also provided roughly 60% of the volume of the river. When one considers that transportation was another of the reasons why the Egyptians depended on the Nile, and that the depth of the river played an important role in setting the speed of the current, the importance of the Blue Nile's impact is clear.
The Blue Nile is much less important to its country of origin, Ethiopia. Known locally as the Abbai, it begins in high, rocky terrain and flows down through an enormous gorge. This gorge is approximately as deep as the Grand Canyon, but is far less accessible. The inhospitable nature of this gorge has not only hindered all efforts at exploration, but it has also served as a barrier for the local population.
Sudan has benefited more from the Blue Nile, also known as the Bahr al Azraq. Sudan relies upon dams for 80% of its electricity. The Blue Nile also supports the irrigation program of the Gezira Plain, a vast project covering more than 2 million acres of farmland. It was the Sudanese who gave the name "Blue" to this tributary of the Nile. When the river is in flood and carrying large quantities of volcanic silt, the water appears to be almost black in color. In this case, the same word was used for the colors black and blue. In the Western world, it was the translation "Blue" that stuck.
The Blue Nile is often overlooked when the Nile is assessed among the great rivers of the world. It is far more important than its modest length would suggest. It supported one of the great civilizations of the ancient world, and even today plays an important role in the economies of its region.