Khartum, where it is joined by the other Nile, called the Bahr-el-Azraq, or "Blue River." The contrast is certainly striking between the two currents, the former being charged with organic remains, turbid, and muddy, while the latter, flowing from a rocky region, is generally much more limpid. But a greater contrast is presented by the variations in their respective volumes according to the seasons. The western branch, which is by far the longest, the distance from Khartum to its still undetermined source being even greater than from that place to the Mediterranean, has also the most uniform discharge. Regulated by the great equatorial lakes, and again by the swampy depressions about Lake No, its contents present comparatively less discrepancies from season to season. But the impetuous Bahr-el-Azraq partakes rather of the nature of a torrent. As soon as the tropical downpours begin to fall on the Abyssinian plateaux, the effect is felt in its rocky channel. Then its discharge exceeds that of its rival, and it was on this ground that Bruce and many subsequent explorers claimed the first rank for the Abyssinian branch. But since the discoveries of Speke, Grant and Baker, it can be regarded only as an important tributary of the Bahr-el-Abiad. Its mean volume is less considerable, nor is it navigable at low water.
The Blue Nile.
On the other hand, if it is the White Nile that maintains the perennial stream, to the Blue Nile is due its fertilising properties. Without the first there would be no Egypt; but for the second the soil of this region would lack its inexhaustible fertility. Not only do the Abyssinians send down their quickening waters to the Nile delta, but they also supply it with the sedimentary matter by which the land is incessantly renewed, and the never-failing return of bountiful harvests insured. In the Ethiopian highlands is solved the mystery of the Egyptian stream, yearly overflowing its banks without apparent cause, and then retiring to its bed after accomplishing its beneficent work. It is to be regretted that the discharge of both rivers has not been accurately determined, the Nilometer at Khartum serving to estimate that of the Blue Nile alone.[1]
At the confluence we at once enter regions known to the ancients. The Bahr-el-Azraq is the Astapus of Ptolemy, whose source was possibly known to the Romans. At least they make it rise in a lake, the Coloe Palus, although placing this lake some twelve degrees south of its actual position. Lake Tana (Tsana) is regarded as the reservoir giving rise to the Abai, which is usually taken as the upper course of the Blue Nile. But if length of course alone be taken into consideration, this honour should rather be awarded to the Beshto, which has its origin some 150 miles farther east. The Tana emissary, however, has the advantage of being much more constant in its discharge, thanks to the controlling action of the
- ↑ Approximate estimate of the discharge of the two Niles at Khartum per second:—
Bahr-el-Abiad. Bahr-el-Azraq. High water •• 175,000 cubic feet. High water •• 213,000 cubic feet. Low water •• 10,000 cubic„ feet.„ Low water •• 5,500 cubic„ feet.„
