1911 Encyclopædia Britannica/Albert Nyanza

From Wikisource
Jump to navigation Jump to search

ALBERT NYANZA, a lake of Central Africa, the northern of the two western reservoirs of the Nile, lying in the western (Albertine) rift-valley, near its north end. The southern reservoir is Albert Edward Nyanza (q.v.) Lake Albert lies between 1° 9′ and 2° 17′ N. and 30° 30′ and 31° 35′ E., at an elevation of about 2000 ft. above the sea. Its greatest length is about 100 m., its greatest width 22 m., its area being approximately 1640 sq. m., about the size of Lancashire, England. South of the lake is a wide plain, traversed by the Semliki river, which enters the Nyanza through a swamp of tall weeds, chiefly ambach and papyrus. Both east and west the walls of the rift-valley are close to the lake, the water in many places washing the base of the cliffs. Elsewhere the narrow foreshore is thickly wooded. The ascent to the plateaus is generally by three tiers of hills rising one behind the other. On the west side the mountains present many pointed and conical summits; on the east the cliffs rise abruptly 1000 to 2000 ft. On either coast wild gorges and ravines, densely wooded, break the outline of the mountains. Through these gorges dash magnificent cascades, others leaping the escarpments of the plateaus in waterfalls of great volume and depth. Towards the north the hills recede from the coast and on both sides flats extend for distances varying from 5 to 15 m. On the eastern side, 92 m. from the southern end of the Nyanza, the Victoria Nile enters the lake, here not more than 6 m. across, through a wilderness of woods, the delta of the Nile extending over 4 m. The mouth of the main stream is obstructed by a bar of its own formation; the current is sluggish; there are many side channels, and the appearance of the lake gives no hint that a great river has joined its waters. For 5 or 6 m. north of the junction of the Victoria Nile the lake suffers no material diminution in width. Then, however, the eastern and western shores approach each other, and a current is perceptible flowing north. The lake has become the Bahr-el-Jebel, or Mountain river, as this section of the Nile is called. Throughout its extent Albert Nyanza is shallow; at its southern end the water for a considerable distance is not more than 3 ft. deep. The deepest soundings give only 50 to 55 ft., the average depth being 30 to 40 ft.

The Albertine Basin of the Nile.—Albert Nyanza receives the whole of the drainage of Albert Edward Nyanza and the Semliki river, and with them and its own basin forms the “Albertine” Nile system. Its waters, as stated above, mingle with those of the Victoria Nile, their united volume flowing north towards the Mediterranean. A study of the changes going on in the rift-valley in which the lakes lie leads, however, to the belief that the Albert Edward and Albert Nyanzas are drying up, a process which the nature of the drainage areas is helping to bring about. That the Albert Edward Nyanza once covered a much larger area than it does at present is certain. At that time, recent from a geological standpoint, the valley to the north, through which now flows the Semliki river, was blocked. The removal of the block led to the shrinkage of the lake and the formation of the Semliki, which found its way to the more northern lake-Albert Nyanza. Gradually the Semliki eroded its bed, and consequently the level of Albert Edward Nyanza continued to fall. The process continues but is checked by the existence of the rock barrier which stretches across the Semliki. This stream leaves Albert Edward Nyanza at its N.W. end in 0° 8′ 30″ S., and after a course of about 160 m. enters Albert Nyanza in 1° 9′ N. In its upper and in its lower course the river flows either through high alluvial plains, in which it has scored a deep channel, or across swamp land. In the middle section, which has a length of some 75 m., the river runs in a deep narrow valley covered with the densest forest. On the west this valley is bounded by the Congo mountains, which form the wall of the rift-valley, on the east by the mighty range of Ruwenzori, whose heights tower over 16,000 ft. above sea-level. In this length of 75 m. the river falls in cataracts and rapids over 800 ft. This rocky barrier acts as a regulator for the water received from Albert Edward Nyanza and, by checking the erosion of the river bed, tends to maintain the level of the lake. When this bar wears away Albert Edward Nyanza will, in all probability, disappear as a lake and will become a river, a continuation of its present most southern affluent, the Ruchuru.

Albert Nyanza, on the other hand, is threatened in the distant future with destruction from another cause—the filling of its bed by the alluvium poured into it by the Semliki, the Victoria Nile and, in a lesser degree, by other streams. The Semliki receives directly or indirectly the whole of the drainage of Ruwenzori, and also that of the eastern face of the Congo mountains as well as the drainage basin of Albert Edward Nyanza. The amount of alluvial matter carried is enormous; from Ruwenzori alone the detritus is very great. Charged with all this matter, the Semliki, as it emerges from the region of forest and cataracts (in which, often closely confined by its mountain barriers, the stream is deep and rapid), becomes sluggish, its slope flattens out, and its waters, unable to carry their burden, deposit much of it upon the land. This process, continually going on, has formed a large plain at the south end of Albert Nyanza, which has seriously encroached upon the lake. At the northern end of the lake the sediment brought down by the Victoria Nile is producing a similar effect. Albert Nyanza has indeed shrunk in its dimensions during the comparatively few years it has been known to Europeans. Thus at the S.W. end, Nyamsasi, which was an island in 1889, has become a peninsula. Islands which in 1876 were on the east coast no longer exist; they now form part of the foreshore. On the other hand, the shrinkage of the lake level caused the appearance in 1885 of an island where in 1879 there had been an expanse of shallow water. It seems probable that, in a period geologically not very remote, the “Albertine” system will consist of one great river, extending from the northern slopes of the Kivu range, where the Ruchuru has its rise, to the existing junction of the Victoria Nile with Albert Nyanza.

The combined drainage area, including the water surface of Albert Edward Nyanza, the Semliki and Albert Nyanza, is some 16,600 sq. m. Throughout this area the rainfall is heavy (40 to 60 in. or more per annum), the volume of water entering Albert Nyanza by the Semliki when in flood being not less than 700 cubic metres per second. Of the water received by Albert Nyanza annually (omitting the Victoria Nile from the calculation) between 50 and 60% is lost by evaporation, whilst 24,265,000,000 cubic metres are annually withdrawn by the Bahr-el-Jebel. The “Albertine” system plays a comparatively insignificant part in the annual flood rise of the White Nile, but to its waters are due the maintenance of a constant supply to this river throughout the year.

Discovery and Exploration.—Albert Nyanza was first reached by Sir Samuel Baker on the 14th of March 1864 near Vacovia, a small village of fishermen and salt-makers on the east coast. From a granitic cliff 1500 ft. above the water he looked out over a boundless horizon on the south and south-west, and towards the west descried at a distance of 50 or 60 m. mountains about 7000 ft. high. Albert Nyanza was consequently entered on his map as a vast lake extending about 380 m. But the circumnavigation of the lake by Gessi Pasha (1876), and by Emin Pasha in 1884, showed that Baker had been deceived as to the size of the lake. By the end of the 19th century the topography of the lake region was known with fair accuracy. The lake forms part of the (British) Uganda Protectorate, but the north-west shores were leased in 1894 to the Congo Free State during the sovereignty of king Leopold II. of Belgium. Of this leased area a strip 15 m. wide, giving the Congo State a passage way to the lake, was to remain in its possession after the determination of the lease.

See Nile; Sir W. Garstin’s Report upon the Basin of the Upper Nile (Egypt, No. 2, 1904); Capt. H. G. Lyons’ The Physiography of the River Nile and its Basin (Cairo, 1906), and the authorities quoted in those works.  (W. E. G.; F. R. C.)