Vol. V, No. 10.] The Rivers of Bengal. 403 
[N.S.] 
‘‘amount of silt carried. While the stream is fully charged 
‘with silt it cannot erode. The silt causes the evil of a 
‘‘shallow river constantly changing its course, but it seems to. 
‘me also to set a limit to the extent of the change, or, at all 
‘‘events to tend to prevent a sudden change to a side channel. 
“‘Thus, we find that proceeding along the spill from Bubia 
“and Hurinugra to Patherdewa, there has been practically 
‘no erosion. The spill channels have banks, but these are 
“entirely composed of the recent silt deposit. In going 
‘down the stream now flowing from Bubia, in a small boat, 
To allow of marginal flood banks being used with any 
ance of success there must be a main channel which is 
perhaps, the best known instance is the basin system of irriga- 
tion in Egypt, by means of which the fertile Nile mud is 
deposited in the basins and the water is then run ol 
a small extent there is the same action during the irrigation of 
rice from the Bengal canals, but here we can only app y 
the water when it is holding a moderate quantity of silt. At 
times of high flood when the water is fully charged, we have 
to shut down for fear of choking the canals. Nature 1s, of 
course, acting in this manner on an enormous scale in the 
delta of the combined Ganges and Brahmaputra, and is con- 
stantly forming, removing and again reforming land. In Orissa, 
in the Puri district, Nature supplies two very good object 
lessons in the Chilka Lake and the Sur Lake. These basins 
receive flood water from two of the branches into which the 
Mahanadi divides. The outlet of the Chilka Lake is to the sea, 
while in the case of the Sur Lake the water flows back, at the 
end of the flood season, by the same channel by which it 
entered. In either case, the silt has been deposited on the 
