The Atbara is a very muddy torrent fed by the rains of north-eastern Abyssinia. It runs for 4 months per annum and is dry for 8 months. Rising within a few kilometres of Lake Tsana, it falls 1500 metres in its first 300 kilometres, and is then joined by the Salaama, and, 100 kilometres lower down, by the Settit river. After the junction with the Settit, the Atbara flows for 480 kilometres and joins the Nile at El Damer, contributing a fair quantity of water and a very considerable quantity of Nile mud to the river.
From the Atbara junction to the sea, the Nile has a course of 2,700 kilometres. In its first length of 1480 kilometres to Assuân it traverses the 5th and 4th cataracts between Berber and Dongola, the 3rd and 2nd cataracts between Dongola and Wady Halfa, and the 1st cataract at Assuân. All these cataracts are navigable in flood, but not so in summer. From Assuân to the Barrage at the head of the Delta north of Cairo, the Nile has a length of 970 kilometres and traverses Egypt without a cataract or interruption of any kind. At the Barrage, the Nile divides into the Rosetta and Damietta branches, and after a further course of about 240 kilometres in either branch, flows into the Mediterranean sea. Its greatest length from the sources of the Kagera river to the sea is 6350 kilometres, constituting it one of the longest rivers in the world.
4. The Slopes and velocities of the Nile in its different reaches.
—[Table 2] of [Appendix B] and [Plate II] comprise all the information available under this head which I have been able to collect. For the slopes I have adopted the following data:
| R. L. of | Lake Victoria | 1129 | metres | above mean sea |
| „ | Fowera | 1060 | „ | „ |
| „ | Lake Albert | 680 | „ | „ |
| „ | Khartoum (flood) | 389 | „ | „ |
From Khartoum to Wady Halfa I have adopted the generally accepted levels of the original Soudan railway survey. From Wady Halfa to the sea I have levelled myself. Upstream and downstream from the adopted levels I have carried the levels by the aid of slopes calculated from velocity and hydraulic mean depth data. It seems to me absurd to adopt a level for Lake Choga 50 metres above that for Fowera, and then to add, that in the 140 kilometres between the two places the Victoria Nile has a gentle slope, wide bed and gentle velocity. By a strange fatality, this very error has crept into the figures under Lake Choga on [Plate II]. The error is noted in the corrigenda attached to the Plate. The Section is drawn correctly but these wrong figures have been interpolated by an oversight.
The Victoria Nile Falls 450 metres in 400 kilometres, but has four reaches; the first 1⁄1200, the second 1⁄20000, the third 1⁄180 past the Murchison Falls, and the fourth 1⁄10000.
The Albert Nile falls 277 metres in 1290 kilometres. The first reach past Wadelai has a slope of 1⁄25000, the second over the Fola and following cataracts has a slope of 1⁄700, the third 1⁄12000, the fourth 1⁄20000, the fifth 1⁄25000, and the last below lake No of 1⁄75000 in flood.
PLATE II.
