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the overflow of the river which runs through them. Even deserted riverains
are apt to be flooded by their original rivers when the waters in these reach an
excessive height.

   Another important feature of the riverains is the fact that the subsoil water is
near the surface. This is equally the case whether the riverains be narrow or wide.
In certain places the rivers have reduced very large tracts to their flood plain level,
as has happened for example in the Jhelum riverain above Shahpur where a tract
more than thirty miles long and on an average more than ten miles broad lies near
flood level. Other examples are seen where the Sutlej near Ferozepore has formed
a great loop northwards leaving a riverain behind it more than ten miles broad, and
north of Lahore city where the thana of Muridke lies in a great depressed area
crossed by old channels of the Ravi and other streams carrying the drainage from
Sialkot.

   Everywhere in such areas the level of the subsoil water is high and after
heavy rain it may remain for months within three or four feet of the surface.

   Between the rivers of the Punjab are strips of country known as the Doabs.
On the whole the lands of the Doabs are at a comparatively high level and they are
much less liable to floods than the riverains. But they are by no means entirely
exempt; for the peculiar conformation of the ground lends itself to the formation
during heavy rains of extensive collections of water. The conditions as regards
subsoil water in the Doabs is stated to depend a great deal upon the amount of
irrigation to which they have been subjected. Throughout most of the Rachna
Doab between the Ravi and the Chenab and the Zech Doab between the Chenab
and the Jhelum the subsoil water is at a considerable depth (40 feet or more).
These Doabs are not only subject to a small rainfall but have only comparatively
recently been irrigated. Throughout the northern portions of the Bari Doab which
lies between the Beas and Ravi and which has been for a long time heavily
irrigated the level of the subsoil water on the contrary is high.

   Over the Doabs rainfall precipitation tends to be diminished as will be seen
from the rainfall maps. There is thus a cyclical tendency for a tract like the Zech
Doab which we shall study in more detail later to have a small rainfall and a low
subsoil water, and to be comparatively free from the liability to floods.

   West of the Jhelum rainfall does not reach proportions sufficient to cause
extensive flooding and such floods as occur arc usually the effects of rivers over-
flowing their banks. But in the eastern half of the Punjab it is doubtful whether
any large tract however situated can be considered free from the possibility of
flooding should an unusually heavy monsoon rain happen to fall there.

   The chief rain of the Punjab is that which falls during the south-west
monsoon. This monsoon breaks as a rule in the Punjab about the middle of June
and continues for about two months. The heaviest rain falls along the eastern

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