<P> Despite covering only about 6.5% of the total area of Egypt; the Nile Valley and Nile Delta are the most important regions, being the country's only cultivable regions and supporting about 99% of the population . The Nile valley extends approximately 800 km from Aswan to the outskirts of Cairo . The Nile Valley is very cool and known as Upper Egypt, while the Nile Delta region is known as Lower Egypt . Steep rocky cliffs rise along the banks of the Nile in some stretches, while other areas along the Nile are flat, with space for agricultural production . In the past, flooding of the Nile during the summer provided silt and water to make agriculture possible on land that is otherwise very dry . Since construction of the Aswan Dam, agriculture in the Nile valley depends on irrigation . The Nile delta consists of flat, low - lying areas . Some parts of the delta are marshy and water - logged, and thus not suitable for agriculture . Other areas of the delta are used for agriculture . </P> <P> The Nile Valley and Delta, the most extensive oasis on earth, was created by the world's longest river and its seemingly inexhaustible sources . Without the topographic channel that permits the Nile to flow across the Sahara, Egypt would be entirely desert . The length within Egypt of the River Nile in its northwards course from three central African sources--the White Nile, the Blue Nile, and the Atbara--totals some 1,600 km . </P> <P> The White Nile, which begins at Lake Victoria in Uganda, supplies about 28% of the Nile's Egyptian waters . In its course from Lake Victoria to Juba in South Sudan, the White Nile's channel drops more than 600 m . In its 1,600 - km course from Juba to Khartoum, Sudan's capital, the river descends just 75 m . In South Sudan, the White Nile passes through the Sudd, a wide, flat plain covered with swamp vegetation and slows almost to the point of stagnation . </P> <P> The Blue Nile, which originates at Lake Tana in Ethiopia, provides on average some 58% of the Nile's Egyptian waters . This river has a steeper gradient and therefore flows more swiftly than the White Nile, which it joins at Khartoum . Unlike the White Nile, the Blue Nile carries a considerable amount of sediment . For several kilometres north of Khartoum, water closer to the eastern bank of the river, coming from the Blue Nile, is visibly muddy, while that closer to the western bank, and coming from the White Nile, is clearer . </P>

What are the major physical features of egypt