Blue Nile. ni Length, width, &c.

to the south and flows in a north-westerly direction towards the Sudan, which it enters near Famaka. after a course of some 500 miles. Altitude at Famaka, 1,700 feet (approx.).

Throughout the whole of this upper portion of its course, which has never been explored, it is believed to flow in a series of rapids over a rockv bed and often between high cliffs, and for the most part through the most precipitous and rugged country. Here it is known as the Abai, whereas, as soon as it reaches the plains of the Sudan, its name at once becomes " Bahr Azrak " or Blue Nile.

Until comparatively recently the Blue Nile was considered by the Abyssinians to be the main stream of the Nile, and they, several centuries ago, fully realised the value of attempting, or threatening, to deprive Egypt of her water supply by the construction of a dam at the outlet of lake Tsana or possibly elsewhere. A mission to study the possibilities of this lake was recently sent from Egypt, and the investigation showed that it is by far the most suitable site on the Blue Nile for the construction of a storage reservoir which, though its benefit to Egypt would be slight, would be of the greatest value to the Sudan.* The length of the Blue Nile, from the point near Famaka, where it enters the Sudan, to its junction with the White Nile at Khartoum, is estimated at approximately 460 miles, which makes its total length about 1,000 miles.

The average width of channel throughout its course in the Sudan is 550 yards. Although in the northern reaches the width increases, it is rarely more than 800 yards wide at any point. The average height of the banks over low-water level is from 26 to 30 feet for the first 150 miles up-stream Banks, from Khartoum. Further south they are higher, and average over 33 to 39 feet above low-water level. The difference in level between flood and low- water is 20 to 23 feet. In the first quarter of the year, the river is reduced to a succession of deep pools, connected by very shallow reaches. Even native boats can with difficulty navigate the distance between Sennar and Khartoum during this season. The Blue Nile is at its lowest in April, but during the latter half of May the first or false rise begins. The real rise begins in June, and the maximum height is attained in August. In the latter half of September it begins to fall rapidly.

Navigation is simple enough at high Nile. As far up-stream as Roseires, 405 miles above Khartoum, the river is navigable by the ordinary Nile steamers from the middle of June till the end of November. Just above Roseires, however, there is a cataract about 6 miles long. This cataract has never been navigated by steamer, but it is said that previous to 1881, sailing boats passed regularly up and down it. Rafts occasionally navigate it successfully on their way down stream. During the last two years a small launch and a few sailing boats have been passed up and down, but there is a dangerous reach for sailing boats above the cataract.

During November and December the water falls rapidly, and sandbanks appear in quantities, the rush of water through the narrow channels being very great. The worst part of the river is near Abdin and Sennar, but there is little rock anywhere. The water for 5 miles below Roseires is bad, and in places dangerous from rock. Steamers with barges lashed alongside, at the end of December in most years, can get through, except at one point some 20 miles south of Sennar, near Abdin, where a reef of rocks extends almost entirely across the river. Steamers have to be steadied over this place by ropes in December, and the barges passed up and down by ropes.

Sir W. Garstin calculates the average discharge of the river at Khartoum to be : — Navigability.

Cataract.

Discharges, t At low-water (May' In flood (August) 200 metres cube per second. 11,000 The velocity of the stream is very great : even in February it is not less than 3 miles an hour, while in full flood Velocity, it must be considerably over 6 miles an hour. In winter the water is very clear, and of a beautiful limpid blue. In ♦ Vvie Foreign Office Blue Book, Egypt No. 2, 1904. t The following table of discharges (Sir W. Garstin's) shows to a certain degree the relative importance of other rivei-s in the Sudan : — Discharge per second.

Bahr El Jebel (Mouth) Bahr El Zeraf (Mouth) Bahr El (Ihazal (Mouth) Sobat (Mouth) White Nile (Khaitoum) Atbara (Mouth) Gash (Kassala) Nile (Berber) Maximum. Minimum 300 m.c. 300 m.c. 140 m.c. 50 m.c.

30 m.c. 15 m.c.

900 m.c. 50 m.c.

1,600 m.c. 300 m.c.

3,000 m.c.

nil.

100 m.c. (?)

nil.

.. 14,000 m.c.

■ (0