Nile

Four miles below Famaka the river is joined on its left bank by the auriferous Tumat, an intermittent stream. In Sennar it receives on its right bank two considerable tributaries from the Abyssinian heights, the Dinder, a very long but not perennial stream, and the Rahad, waterless in the dry season, copious and richly charged with sediment during the rains from June to Sept. At this period the discharge of the Blue Nile rises from less than 200 to over 6,000 cu. metres per sec., thus greatly exceeding that of the White Nile itself, which is only from about goo to 1,500 cu. metres during the flood. The length of the Blue Nile is about 85o m. The country, El Gezira, enclosed in the triangle formed by the junction of the White and Blue Niles forms the most fertile por tion of the Sudan, and the portion now irrigated from the Blue Nile is producing excellent cotton crops and durra.

The Atbara.

Two hundred miles below Khartoum—at Ed Damer—the Nile is joined by the last of its tributary streams— the Atbara or Bahr-el-Aswad (Black river). The Atbara, some Boo m. long, rises in the tableland north of Lake Tsana, being formed by the junction of the Angreb, Salaam, Aradeb, Goang and other mountain streams. Making its way towards the Nubian plains, the river flows in a north-westerly direction, joining, in 14° 1o' N., 36° E., the Bahr Setit or Takazze (see ABYSSINIA), a river coming from the east and having a volume of water as large as, if not larger than, the Atbara. The united stream pre serves, however, the name of Atbara, and at its confluence with the Nile has a breadth in flood time of over 600 yd. and a volume which exceeds 2,000 cu. metres per sec. in August. The Atbara and its tributaries, like many of those which feed the Blue Nile, rapidly dwindle after the rains. In its lower course the Atbara runs completely dry, but higher up water may be found in deep pools. These pools are full of fish, turtles, crocodiles and hippo potami, which remain imprisoned until the return of the flood. The country between the Nile proper, the Atbara and the Blue Nile is identified with the island of Meroe of ancient history.

The Cataracts.

Below the Atbara junction the Nile continues its course to the Mediterranean, traversing a distance of over 1,60o m. without receiving a single tributary on either bank. Below Khartoum the river makes a great S-shaped bend, and leav ing behind the cultivable land, traverses the Nubian desert. In its progress the volume of water suffers continual diminution from evaporation, owing to the extreme dryness of the air. The valley of the river is here very narrow, and the desert land in places comes right to the water's edge. Elsewhere high and barren cliffs shut in the valley. Between Khartoum and Wadi Halfa (the northern end of the great bend), a distance of over goo m., occurs a series of cataracts, known as the 2nd, 3rd, 4th, 5th and 6th (the 1st cataract is lower down the river at Assuan). That first met

with on descending the river from Khartoum is the 6th (or Shabluka) cataract. The river here (5o m. below Khartoum) is picturesque, flowing -rapidly in a narrow gorge for 8 m., but the fall is only 2 ft. After 188 m. of smooth water the 5th cataract is reached. It begins 28 m. below Berber (a town on the right bank at the head of a caravan route to the Red Sea), and with three principal rapids extends for ioo m.—the drop in this dis tance being rather more than 8o ft. At the foot of this cataract is the town of Abu Hamed, at the eastern end of the middle of the S bend. The 4th cataract begins 6o m. down stream from Abu Hamed. It is 8o m. long and has a drop of 110 ft. Between the 4th and 3rd cataracts there is a stretch of 200 m. on a very gentle slope This reach cotstitutes the province of Don gola, and here the cultivable land on the western side of the river is of greater extent than usual in the desert zone. The 3rd cataract, 45 m. long, has a drop of some 36 f t. After another smooth reach extending 73 m. the 2nd cataract, which ends just above Wadi Half a, the northern frontier town of the Anglo-Egyptian Sudan, is reached. This cataract is 124 m. long and has a fall of 216 ft. Between the 2nd cataract and Assuan are 214 m. of smooth water with a scarcely perceptible slope, . The average breadth of the river here is 1,640 ft.

Lower River and Delta.—For some distance above Assuan the river is studded with islands, including those of Philae and Elephantine. The rapids south of the town used to form the 1st cataract, where, in a length of 3 m., the river fell 161 ft. Since the completion of the great dam and locks at the head of these rapids they have to a certain extent disappeared, and a navigable channel has been formed. The dam, pierced by 18o sluices, stretches across the river—a wall 2,00o yd. long below which the water rushes between rocks in many channels (these being the relics of the cataract). Upstream from the dam a lake some ioo m. in length has been formed. The Assuan Dam was opened on Dec. 1o, 1902 (see under IRRIGATION). A ladder of four locks on the western side of the dam permits navigation between the upper and lower reaches. At Assuan the banks of the river are bordered by high granite hills. From this point to the apex of the delta the length of the Nile is 605 m. with a slope ) even slighter than that above Assuan. The valley is comparatively narrow, being an almost level depression in a limestone plateau and the area of fertility ends where the land ceases to be irrigated by the river. At Esna, 10o m. below Assuan, a barrage, known as the Esna barrage, regulates the flow of the water, and at Assiut, 345 m. below Assuan, is another barrage fulfilling the same purpose, and a third at Nag Hamadi, about 215 m. below Assuan was under construction in 1928. Cairo stands on the eastern bank of the Nile I2 TM south of the apex of the delta.