— 37 — 
tif ul and especially heavy in autumn, and were it not for the extensive 
lakes and marshes in its middle course, it would be a torrent in flood. 
Regulated and restrained by the lakes and marshes, this river has an 
extraordinarily even rise and fall, as a reference to Table 2 4 will certify. 
It is unfortunate that the Nasser gauge has been read so interruptedly. 
The Doleb Hilla gauge is in the back water of the Albert Nile and not 
very reliable. The discharges of the last four years have varied from 
40 cubic metres per second in low supply to 1000 cubic metres in flood, 
though there have been years when the discharges have fallen to zero 
in summer and when the flood must have exceeded 1500 cubic metres 
per second. April is the month of low supply and November of max- 
imum flood. 
In its last 50 kilometres, the river has a deep, well defined channel 
between high banks, which are never topped in the highest floods. The 
width of waterway is about 110 metres and the depth 7 metres in 
summer and about 10 to 11 metres in flood. 
The principal tributaries of the Sobat are the Baro from the north 
east and east, and the Akobo and Pibor from the south-east and south. 
All the tributaries meet and form extensive swamps from which the 
Sobat has its origin. The village of Nasser is situated on the Sobat 
near its origin. A gauge has been erected here. 
17 . The Sudd region. — The Sudd region of the Albert Nile lies 
north of Ghaba Shambe and corresponds to that part of the river where 
not only do the floods overflow the banks, but the summer supplies 
can do so in many places. It is the delta of the river in a very embryo- 
nic stage. There are two main branches to the river, the Albert Nile 
proper and the Zeraf , which have both been already described. Both 
these rivers are liable to be blocked by sudd or blocks of living vegetation. 
These blocks are sometimes as much as 5 metres thick and capable of 
turning nearly the whole supply of the river out of its course. They 
are formed of papyrus, weeds and watergrasses, which grow on the 
half sandy half peaty banks of the lagoons and marshes traversed by the 
river, and which, under the double action of a rising flood and strong 
winds, are torn up and driven into the channels wherever they are con- 
fined in width, and there jammed into solid masses of floating weeds, 
filling the whole width of the river, very nearly the whole depth, and 
sometimes over a kilometre in length. In addition to the local weeds 
and grasses, there are always at hand in high floods dense masses of pistea 
weeds which have come from the upper waters of the Albert Nile south 
