Of the flood water annually brought down by the rivers, about half now runs to waste into the Mediterranean sea. The Aswan dam regulates and utilizes this to a certain extent, but a large proportion remains over. This it is proposed to utilize in the future for irrigating the Sudan by means of flood and catchment basins; but the time is still distant when this surplus will be entirely devoted to this purpose.
Historical.Up to comparatively recent times the sources of the Nile were involved in mystery.[18] In ancient days many guesses were hazarded at their origin, some geographers maintaining that the Nile rose in the Atlas Mountains of Marocco; others were positive that the Niger formed the upper portion of the great river. During the 17th and 18th centuries it was held that the sources were to be found in the “Mountains of the Moon.” These have since been speculatively identified with the Ruwenzori Mountains between Lakes Albert and Albert Edward, and, if this theory is correct, the ancient geographers were not so far out.
It was left for Speke and Grant, in 1862, on a journey from the east coast, to discover that the great lake, now known as the Victoria Nyanza, was the main source of the White Nile. Sir Samuel Baker, in March, 1863, working up stream, discovered the Albert Nyanza; but it was not till some time afterwards that the actual course of that portion of the river, now known as the Bahr El Jebel, was mapped and traversed, Lieutenants Watson and Chippendall, R.E., being the first, under Gordon in 1874, to lay down the actual course. During the ensuing years, this, the upper portion of the river, was several times blocked with sudd, and at the re-conquest of the Sudan from the Dervishes in 1898, it was permanently blocked. An expedition under Major Peake, however, succeeded in clearing a channel in 1899-1900, and there is no likelihood of the clear channel now existing being, except quite temporarily, blocked again.
The sources of the Blue Nile, which for long was considered as the main river, were, as early as 1770, discovered by Bruce to be near Lake Tsana (Abyssinia), but to this day the actual course of the Blue Nile between Lake Tsana and Famaka (Abyssinian-Sudan border) has never been accurately laid down.
The course of the Atbara, as far up as the junction with it of the Setit, was roughly known before 1864, when Sir S. Baker made a more thorough exploration of these rivers, but the courses of the Atbara and Setit lying within the Sudan have only recently been fairly accurately laid down. The Atbara rises in the Abyssinian hills, near Chelga, where it is known as the Goang.
The Sobat was explored by Marno and Junker in the “Seventies” as far as Nasser, where there was then an Egyptian post. It was left for British officers, after 1898, headed by Captain Gamble, to explore the various narrow rivers such as the Baro, Pibor, Akobo, etc., which join the main stream from South-West Abyssinia, east of Nasser. The course of the Upper Pibor was explored by Lieut. Comyn in September, 1904, vide [p. 151.]
The course of the comparatively short Bahr El Ghazal river, known to the slave-traders of old times, was laid down by Petherick, Gessi, etc., in 1864-78; but the courses of the western rivers which flow into it, such as the Bahr El Arab[19] or El Homr, have not yet been even roughly determined. Those of the more southerly affluents, such as the Suei or Jur, etc., though not yet accurately fixed, have been sketched in by Junker, Marchand, etc., and the British officers in the Bahr El Ghazal since 1900.
(ii.)—GENERAL DESCRIPTION (DOWN STREAM).
Albert Nyanza to Khartoum, Bahr el Jebel.After leaving the Albert Nyanza, the White Nile (or as it is there called the Bahr El Jebel) flows for 110 miles in a deep broad arm, with scarcely any velocity or slope, past Wadelai and Dufile to Nimule, and then, after a short and troubled course, between high mountain ranges, tosses over the Fola Rapids in a channel only 50 yards broad. From here it continues in a torrent to about Rejaf. Here the river is 7 feet deep at low Nile and 15 feet at flood time, discharging between 18,000 to 60,000 cubic feet per second. The regulating effects of the great lakes are well felt here. It is here at its lowest in winter; begins to rise about 15th April, with a minimum about the end of August.
From Rejaf to Bor, 112 miles, the river is mainly in one channel with a rapid fall. From Bor to the junction with Lake No, 384 miles, the river meanders along in numerous marshy channels with a very gentle slope. The main channel always used is known as the Bahr El Jebel. In this reach are the dams of living vegetation, known as the “Sudd” (for description see [Appendix B]). On one stretch the true channel is still blocked with sudd, and a “false” channel, a little to the westwards, has to be used for about 20 miles.