Lake No.At the junction of the Bahr El Ghazal and the Nile in north lat. 9° 29′ is Lake No, or Moghren El Buhur,[20] a shallow expanse of water surrounded on all sides by reedy marsh and varying in size according to season, but in summer probably about 60 square miles. It forms a reservoir for the sluggish streams that drain the extensive plateau forming the water-shed between the Nile and Congo. In summer the lake and its swampy surroundings act as an evaporating basin, and the loss of water is consequently considerable. The waters here also become polluted with decaying green vegetable matter.
The Bahr El Ghazal enters Lake No at its western extremity, and the Bahr El Jebel passes through its eastern end. The Bahr El Ghazal has a feeble discharge and has no effect at any time on the volume of the White Nile.
In the stretch between Lake No and the Sobat, 81 miles, the current is slow and the channel occasionally blocked by sudd.
Sobat.During flood, the Sobat has a discharge nearly equal to that of the Bahr El Jebel above the junction. In the spring the discharge from the Sobat is feeble, and the river is then unnavigable. The soil brought down by the Sobat is light and friable.
White Nile.At the Sobat confluence the river changes its name[21] and now becomes the Bahr El Abiad or White Nile.
From this point down to Omdurman, 530 miles, it receives no more perennial affluents, but several large khors join it on the east bank between Kodok and Renk—chief of which are Khor Adar and Khor Rau.
The White Nile flows sluggishly along with a low velocity and gentle slope; its course is generally straight and its section wide and shallow, banks low, supply very constant; the colour and limpidity of its water show very little change throughout the year, and the variations between the level of high and low supply are very small, being not more than 2 to 6 feet. The depth of the river in this stretch ranges from 15 feet at low Nile to 21 feet in flood. In parts, the channel in flood time is often of immense width.
The result of 94 measurements made in June, 1862, show the mean width of the river in flood to be 1,870 yards. In many places, however, the channel is more than 2 miles wide, and in its general appearance it resembles a lake rather than a river. Its banks, more particularly the western shore, are very low, and its waters in flood spread for several miles over them. Their average height is not more than 8 to 10 feet above low water level, and the maximum difference between high and low supply is not more than 6 feet.
The river is at its lowest by the beginning or middle of April; the rainfall in the south then causes a constant and gradual rise, but the flood does not reach its maximum before the beginning of September.
The velocity of the current when in full flood is not more than 2½ to 3 miles an hour, whilst in winter this is reduced to 1½ miles an hour. The water is of an olive green or yellowish brown tinge. It owes most of its colour to the creamy-white waters of the Sobat River, called by the Arabs the Bahr El Asfar, or Yellow River.