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 come the rains, and a great flood comes down, invading a still greater area ; but this is probably covered with brushwood and vegetation, and the river is prevented from cutting away the soil, but encouraged to deposit its silt, so that, as the supply of melted snow and rain-water ceases, these lands are left by the subsiding river higher than they were before. In succeeding years, unless an exceptionally high flood should come down, the river will be less liable to cover these lands, and the general effect, therefore, of the annual rise of the river is to confine it within narrower limits, for the banks on either side are gradually raised. The Indus, however, not only raises its banks, but also raises its bed, and flows at a higher level than the surrounding country ; it has, therefore, to be confined for many miles between artificial banks, the duty of preserving which is one of the most unpleasant, which may fall to the lot of a canal engineer in Sind.

Now, while the river is in flood, it flows in a straight course and in short cuts across its loops. At the lower end of each short cut there is a sudden drop in the bed, and a greater velocity, the result of which is the erosion of the alluvial mud to such an extent that the projecting spur (now under water) may be cut right through, and the main channel of the river entirely altered.