Two things define the Nile for almost 2000 km from Khartoum to Aswan: the cataracts and the great bend. The cataracts are sections where the river tumbles over rocks and have long kept boats from going up and down the river from Equatorial Africa to Egypt. There are six classical cataracts, but there are really many more. The cataracts are also significant because these define river segments where granites and other hard rocks come down to the edge of the Nile. The floodplain is narrow to nonexistent here, and opportunities for agricultural development is correspondingly limited. These two reasons - navigation obstacles and restricted floodplain - are the most important reasons why this part of the Nile is thinly populated and why the historic border between Egypt in the north and Nubia or Sudan in the south is the First Cataract at Aswan. The great bend is one of the most unexpected features of the Nile. For most of its course, the Nile flows inexorably north, but here in the heart of the Sahara, it turns southwest and flows away from the sea for 300 km before resuming its northward journey. This deflection of the river's course is due to tectonic uplift of the Nubian Swell over the past 100,000's of years. This uplift is also responsible for the cataracts - if not for recent uplift, these rocky rivers stretches would have been quickly reduced by the abrasive action of the sediment-laden Nile.
The great bend is one of the most unexpected features of the Nile. For most of its course, the Nile flows inexorably north, but here in the heart of the Sahara, it turns southwest and flows away from the sea for 300 km before resuming its northward journey. This deflection of the river's course is due to tectonic uplift of the Nubian Swell over the past 100,000's of years. This uplift is also responsible for the cataracts - if not for recent uplift, these rocky rivers stretches would have been quickly reduced by the abrasive action of the sediment-laden Nile.
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The cataracts hinder navigation of the Nile, and have done so for thousands of years. The ancients used the strong north winds to sail up the Nile in Egypt, but this could not carry them over the cataracts. Instead, the boat would have to be dragged up the cataract by teams of men, often with great difficulty. Click here to see how this was done.
The best description of cataracts comes from 'The River War', written in 1899 by Winston Churchill, then 25 years old. The book details the exploits of the British in 1896 through 1898 to return to the Sudan after they were chased out by the Sudanese people in 1885. The British tried to reconquer the Sudan by steaming in gunboats up the Nile, so they were very interested in how the water flowed through the cataracts. They knew that the only time that ships could move upstream through the cataracts was during the summer flood, and then only with great difficulty. Churchill describes the Second Cataract (now submerged beneath Lake Nasser) as being about 9 miles long and having a total descent of sixty feet. The river flowed over successive ledges of black granite. During the summer floods, the Nile flowed swiftly but with an unbroken surface, but the granite ledges were exposed when the annual flood abated. During this time, Churchill reported that the river tumbled violently from ledge to ledge, its entire surface for miles churned to white foam. There are several other small cataracts between the Second and the Third Cataracts (Churchill shows cataracts near Semna, Ambigol, Tanjore, Okma, and Dal) but none of these posed any problems to the British moving upstream. According to Churchill, the Third Cataract is "a formidable barrier." There is smooth water for 200 miles upstream from this in all seasons.
The Fourth Cataract lies in the Monassir Desert, and Churchill reported the following about this portion of the Nile: "Throughout the whole length of the course of the Nile there is no more miserable wilderness than the Monassir Desert. The stream of the river is broken and its channel obstructed by a great confusion of boulders, between and among which the water rushes in dangerous cataracts. The sandy waste approaches the very brim, and only a few palm-trees, or here and there a squalid mud hamlet, reveal the existence of life." The British gunboats El Teb and Tamai in 1897 attempted to go up the river at the Fourth Cataract, but in spite of being helped by 200 Egyptians and 300 tribesmen, the Tamai was swept downstream and almost capsized in the great rush of water. Four hundred more tribesmen were assembled to help the El Teb, which was capsized and carried off downstream.
The Fifth and Sixth Cataracts are regions of swift and rough water, but can be navigated all year round.
Ground Images of the Cataract Nile
Satellite Images of the Cataract Nile
The Great Bend of the Nile is a much bigger feature than its nearest competitor, the Big Bend of the Rio Grande.