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interminable marshes of papyrus and water grasses. The Gazelle river 
is a deltaic river in a still more embryonic stage than the Albert 
Nile north of Ghaba Shambe. It, however, performs one good function. 
It keeps the swamps of the Sudd region full of water, year in and 
year out; and without it, the water of the Albert Nile would doubtless 
be lost by percolation in the Sudd region and the White Nile be left 
high and dry for 3 months every year. 
Schweinfurth was the first to ascend and describe this river and its 
tributaries. Beginning from the east, its principal tributaries are: — 
the Rohl, the Dyow, the Tondy, the Kit, the Dyur, the Dembo, the 
Humr and the Bahr el Arab. With courses of between 450 and 750 
kilometres in length, the tributaries fall from 500 to 700 metres 
in their upper courses of from 300 to 500 kilometres, and in their 
remaining courses they traverse swamps. Certain of the tributaries 
may be discharging 10 cubic metres per second in summer and 250 
cubic metres per second in flood, but the main stream of the Gazelle 
seems never to add more than 40 cubic metres per second to the Albert 
Nile. The whole of the water is evaporated from the weeds, papyrus, 
watergrasses and open sheets of water which cover a desolate area of 
70,000 square kilometres. Evaporation and rainfall balance each other. 
If the (( Singhara » or Indian water nut could be induced to grow in this 
waste of waters, some profit might be got out of them. 
15. The Bahr Zeraf. — -The Bahr Zeraf is the right hand branch 
of the Albert Nile which leaves the latter river north of Ghaba Shambe 
and joins it again midway between Lake No and the Sobat river. It 
is fed largely by the escape water of the Atem river brought down in 
a traceable channel and in flood by torrents from the hilly region east 
of Gondokoro. Beginning with a series of marshes and swamps, it gra- 
dually establishes its right to be called a river and finally after a tortuous 
and meandering course of about 270 kilometres tails into the Albert 
Nile. In its lower reaches it is about 50 metres wide and from 2 to 4 metres 
deep in summer and 6 to 8 metres deep in flood. Its discharges vary from 
30 cubic metres per second in summer to 160 cubic metres per second 
in flood. In its lower reaches the banks consist of solid earth, proving 
that at one time it carried water other than that brought down by the 
Albert Nile. 
15. The Sobat River. — This river drains 156,000 square kilo- 
metres lying between the catchment basins of Lake Rudolf and the Blue 
Nile. The rainfall in the mountainous region of Gallaland is plen- 
