According to localcollegeexplorer, the climatic conditions of Egypt are not such as to allow the formation of perennial streams. The Nile, the only river that crosses the country, is not fed by the rains that have fallen locally but draws its waters from the great lakes of central Africa and from the mountains of Ethiopia, and its flow decreases from upstream to downstream due to the evaporation and infiltrations, increased dramatically by the practice of irrigation, which can be said to be widespread along its entire course through Egypt, which runs from the Sudanese border, located 46 km. to N. of Wādī Ḥalfā, up to Rosetta it measures 1508 km. (see nile).
This aridity means that all the lakes and ponds, which are found in good numbers in the country, have brackish or salty waters. Most are, moreover, coastal lagoons of the Delta, shallow and separated from the sea by a strip of land no wider than about fifteen km., Sometimes much less, up to a few hundred meters. They are all rich in fish and hunting. The first to the west is Lake Maryūṭ (the Palus Maraeotis degli ancients), located in S. di Alessandria (v.), varying in size and height according to the level of the waters in the Nile. The waters during the floods take on an extension of over 250 square kilometers. and are lowered by means of powerful pumps, since the lake is now devoid of communication with the sea. Navigable in antiquity and then joined with canals to the Nile, it became a salt plain in the Middle Ages; this was artificially flooded by the English army encamped in Abukir in 1801, cutting a channel in the beach and thus submerging vast cultivated areas. The region around in Roman times was largely cultivated and fertile with vineyards and adorned with villas. To the Egypt of Lake Maryūt, between it and the Rosetta Nile, is Lake Edkū, 35 km long. and wide, at times, up to 26 km., communicating with the sea in the bay of Abukir. Between the Nile of Rosetta and that of Damietta is the 100 km long lake el-Burullus. and 26 wide, edged in S. and SE. from marshy soils and fed by canals and secondary branches of the Nile, including the Baḥr-Mīt-Yazid which flows in front of the lake’s mouth into the Mediterranean, an outlet corresponding to the ancient Sebenitic arm of the Nile.
El-Manzalah, the largest of the Delta lakes (64 km long, 24 km wide, 2000 sq km area), extends between the Damietta branch and Port Said, separated from the sea by a narrow strip of land that the waves overtake in the storm surges, making the waters salty. Numerous canals lead into it, one of which corresponds to the Mendesio branch, another to the Tanitic branch of the Nile: both important in antiquity; several islands, partly inhabited by fishermen, like the shores where a few herds of buffalo still live; there are also numerous rocks, full of water birds: pelicans, herons, flamingos. Along the eastern edge of the lake, the Suez Canal was dug for a length of 32 km. beyond this the lake is reduced to a marshy plain, in which salt pans have been created and through which the Pelusiaco branch flowed,
Between Tell el-Faramah, where ancient Pelusio stood, and el-‛Arīsh, along the northern coast of the Sinai peninsula (v.), Extends over a length of 85 km. and with a maximum width of over 20 km., another large coastal lagoon, the Sabkhet el-Bardawīl, bordered to the South. by vast dune areas and bounded to the North. by a narrow coastal strip on which the road from Porto Said runs to el-‛Arīsh.
The lakes of the Isthmus of Suez are smaller, and were very salty before the Suez Canal (v.) Joined them on one side to the Mediterranean, on the other to the Red Sea. They are lake el-Ballāḥ, separated from el-Manzalah by a narrow strip of land called el-Qanṭarah (the bridge), lake et-Timsāḥ, on whose northern shore is Ismailia (v.), And the so-called Bitter Lakes (perhaps the “Mara” of the Bible), the bottom of which is 8-12 meters below sea level. These actually constitute a single basin throttled in the southern third, so as to form the Grande Lago Amaro in N. and the Piccolo Lago Amaro in S.
A series of 10 lakes rich in natron (sodium carbonate) is found in Wādī en-Naṭrūn, 110 to 150 km. to the West of Cairo, about fifty km. from the railway, to which it is connected by a private line of the company that exploits the salt deposits of the valley. This is also known for the Coptic convents and for the layers rich in fossils and petrified trunks. Further to S., in the province of Fayyūm, is the Birket Qārūn, a lake of brackish water, in communication with the Nile (see fayyūm).
The effect of local rains, negligible compared to the Nile and stagnant waters, is however sensitive in the shaping of the soil and in the feeding of underground aquifers. The mountain ranges that make up the Arabian Desert as a whole, and even more the Sinai mountains, are in fact subject to rainfall that is not entirely insignificant, at least judging by the valleys, which are normally dry but active during those valleys. In fact, almost every year, the water runs for a few hours, sometimes for a few days, in the deep and tortuous furrows of the w ā d ī which, cluttered with blocks and sand, descend from the el-Ma‛azah plateaus or from the Etbāi mountains towards the right bank of the Nile, such as the Wādī eṭ-Ṭīh, the W. Ḥōf near Ḥelwān, the W. ẹt-Ṭarfeh to N. of Minyā, the W. Shetun and the W. el-Miyāh in the plateau to the SE. of Asyūṭ, the very long and important Wādī Qinā, the Wādī el-Kharīṭ with its numerous tributaries, the Wādī el-‛Allāqī in S. of Aswan and many other minor ones.
On the reverse of these reliefs towards the Red Sea, the valleys are generally shorter, since the watershed runs mostly closer to this than to the Nile: important are, in N. the W. er-Ramlīyah, the W. Batat and the Wādī el-‛Arabah; further to S. we will remember the W. ed-Dīb opening into the bay of ez-Zeit, the W. Abū Marwah with its many tributaries in the bay of Gimsah, the W. Ambagi in el-Qoṣeir; from here to beyond Rās Banās i w ā d ī they also become shorter and simpler due to the proximity of the mountains to the coast; between Rās Banās and the 22 ° N. we mention the Wādī el-Ḥōdein, the W. Ibib and the W. Kiraf, which originates in the Sudanese territory.
Analogous are the w ā d ī of the Sinai peninsula: longer and more branched those of the northern slope that turn to the Mediterranean, shorter, but more active due to the greater elevation of the mountains, those that descend from Gebel Mūsà and G. Kātherīnā to Gulf of Suez or the Gulf of el-‛Aqabah (see S inal).
In all these unique valleys, active very few days of the year, more often one day every many years, the flood (which the Arabs call sail) sometimes reaches the Nile or the sea, but more often they just sweep away the poor crops and the valley bottom paths: once you reach the plain, the waters get lost in the sand or collect in some depression. In any case, the landscape of the Arabian Desert, like that of the Sinai, clearly shows the shaping action of running waters, in contrast to that of the Western Desert, where the actions of erosion and wind sedimentation absolutely predominate, and valleys are insignificant.
These rains, although scarce and occasional, determine the formation of groundwater, which nourish a thin shrub vegetation in the valley floor and feed numerous wells, precious for nomadic shepherds, whose life depends greatly on this rainfall. Springs such as those of Abū Sa‛fah and Abraq near the Red Sea in S. di Rās Banās, and those of Wādī el-‛Arabah in the Thebaid, which the monasteries of S. Paolo and S. Antonio draw on, are fed from precipitation and correspond to a specific geological level of the Middle Cretaceous period (Nubian sandstones). Generally, however, in the coastal region of the Red Sea, groundwater and spring waters are scarce and rich in salts (selenitose, salty, etc.).
In the Libyan Desert the sources are much rarer, however they are not entirely lacking: an aquifer level, corresponding to soils of the upper Cretaceous period, determined the position of some minor oases (el-Kurkūr, ed-Dunqul). However, most of the groundwater is supplied by the infiltrations of the Nile or by the precipitations that the Nubian sandstones absorb in the Sūdān and convey into the subsoil of Egypt. The first category includes the waters of the numerous wells opened in the floods of the Nilotic plain, generally at about 40 m. depth. The river loses water to the permeable layers of the soil in the months of floods, from July to November, and reabsorbs part of it from December to June. The water is hard, rich in iron and manganese oxides, but in general drinkable and abundant, so that important centers such as Ṭanṭā and until recently even Cairo itself, depend entirely on it. However, the water of the Nile, suitably filtered, is preferable; and Cairo today drinks of that. In the northern part of the Delta, where large brackish marshes predominate, water is scarce at a small depth or is rich in salts, but it seems that there is discrete water at greater depths. Here the local precipitations contribute significantly to the feeding of the wells, when they are collected from the sand of the coastal dunes. The abundant underground waters that flow naturally or are artificially reached through deep artesian wells, in the great oases of the Libyan Desert, such as el-Khārǵah, ed-Dākhlah and el-Baharīyah, which owe their existence to them.
