THE WHITE NILE.
[The reader who wishes to study in detail the whole question of the Nile Basin, its floods, discharges of rivers, schemes of irrigation, etc., etc., is referred to Sir William Garstin’s invaluable “Report on the Basin of the Upper Nile,” F.O. Bluebook, Egypt No. 2 (1904). Price 17s.]
(i.)—INTRODUCTORY.
General.The White Nile and its tributaries form the life blood of the Sudan. The great river traverses it for 2,029 miles from south to north, receiving on its course through the country the Bahr El Ghazal, the Sobat, the Blue Nile, and the Atbara.
Of these four tributaries the Bahr El Ghazal joins the Nile out of the swamps from the west, whilst the other three join it from the east, bringing down the fertilizing matter from the Abyssinian hills.
Flood.The rise of the Nile takes place during the summer, but the dates naturally vary largely at different points.
The causes of the flood are, briefly, as follows:—The rains in southern Abyssinia cause the Sobat to rise about the middle or end of April. The yellowish-white water caused by this flood reaches Kodok the last week in April. The equatorial rains cause the Bahr El Zeraf and White Nile, above the Sobat, to rise about the end of May. The effect of the first rise is felt at Halfa about the 20th May. The Blue Nile begins to rise about this time, and brings the red fertilizing flood down to Khartoum about the 20th June, and to Halfa about the middle of July. The muddy Atbara flood (June to August) rises very rapidly after the Blue Nile, and causes the flood to attain its maximum about the end of August; at this period the river is muddiest. The White Nile continues to rise slowly, and its effects (clear white water) are felt at Halfa till October, when it falls very slowly. The Blue Nile falls rapidly after the middle of September, and the Atbara has generally disappeared by October. The Sobat begins to fall at Nasser early in December.
The Bahr El Ghazal rivers rise slightly in May. These soon subside, and the main floods take place in July and August.
The above is a description of an average year. An early maximum (i.e., about the middle of August) generally means a low summer flood, and vice versâ. The flood at its height moves at about 100 miles a day (below the Atbara).[17]
The above dates vary largely in accordance with the time and amount of rainfall in the upper valleys of the rivers.