The altitude of Egypt ranges from 133 m (436 ft) below sea level in the Libyan Desert to 2,629 m (8,625 ft) above in the Sinai Peninsula. The Nile Delta is a broad, alluvial land, sloping to the sea for some 160 km (100 mi), with a 250-km (155-mi) maritime front between Alexandria (Al-Iskandariyah) and Port Sa'id. South of Cairo, most of the country (known as Upper Egypt) is a tableland rising to some 460 m (1,500 ft). The narrow valley of the Nile is enclosed by cliffs as high as 550 m (1,800 ft) as the river flows about 900 km (560 mi) from Aswan to Cairo. A series of cascades and rapids at Aswan, known as the First Cataract (the other cataracts are in the Sudan), forms a barrier to movement upstream.
The bulk of the country is covered by the Sahara, which north of Aswan is usually called the Libyan Desert. East of the Nile, the Arabian Desert extends to the Red Sea. The Western Desert consists of low-lying sand dunes and many depressions. Kharijah, Siwah, Farafirah, Bahariyah, and other large oases dot the landscape; another lowland, the Qattara Depression, is an inhospitable region of highly saline lakes and soils covering about 23,000 sq km (8,900 sq mi). The outstanding topographic feature is the Nile River, on which human existence depends, for its annual floods provide the water necessary for agriculture. Before the completion of the Aswan High Dam in 1970, the floods, lasting generally from August to December, caused the river level to rise about 5 m (16 ft). Now, however, floodwaters can be stored, making it possible to provide year-round irrigation and to reclaim about 1 million feddans (about 1.04 million acres) of land. Damming the Nile resulted in the creation of Lake Nasser, a reservoir 292 km (181 mi) long and 9–18 km (6–11 mi) wide.