2 White Nile.

water is consequently considerable. The waters here also become polluted with decaying green vegetable matter.

The Bahr el Ghazal has a feeble discharge in summer, but occasionally exceeds the Bahr el Jebel when in flood.

In the stretch between the Bahr el Ghazal and the

Sobat, 80 miles, the current is slow, and the channel is

occasionally blocked by sudd.

During flood the Sobat has a discharge nearly equal to that of the Bahr el Jebel above the junction. In summer the discharge from the Sobat is feeble, and the river is occasionally quite dry. The soil brought down by the Sobat is light and friable.

Here the river changes its name* and now becomes the Bahr el Abiad, or White Nile. From this point down to Omdurman, 505 miles, it receives no more affluents, except occasional tributes in very rainy seasons from several small khors on th'e east bank. The breadth of the river in this stretch varies considerably at different

points, but averages about a mile at high Nile, and the

depth ranges from 15 feet at low Nile to 23 feet in flood time.

The current is sluggish, and its action is nearly throughout on the right bank, owing to the prevailing north-west winds. Bottom sandy in parts, but mostly mud.

Junction of the Niles at Khartum.

At Khartum half Nile usually occurs about the middle

of July ; high Nile at the end of August or beginning of

September, lasting about a month. Half Nile end of November ; lowest Nile in April. Maximum Blue Nile flood about 25 th August. Its mean

discharge at high Nile at Khartum is 8,000 tons (280,000 cubic feet) per second.

In flood the discharges of the two Niles are nearly equal, but from November to March the White Nile is the main source of supply.

The average difference here between low and high Nile

is 22 feet (17J to 26 feet).

The Blue Nile branch east of Tuti Island is sometimes

dry at low Nile.

* According to some, the change takes place at Lake No.