In Ceylon, for instance, the
whole rainfall of the year occurs within a period of six to eight weeks,
and often amounts to as much as 12 in. in the twenty-four hours, and has
been known, comparatively recently, to reach nearly 19 in., the latter an
amount only 2 in. or 3 in. less than the average rainfall of Lincolnshire
for the whole year. In London it is only 25 in. and in the wettest
district in Great Britain, viz., Cumberland, averages not more than 70
in. per annum.
The rainfall in Bombay is from 80 in. to 100 in. per annum, and
throughout India may be taken as from 50 in. to 130 in., varying, as is
the general rule, in direct ratio with the altitude, and limited to a few
weeks in the year. Notwithstanding this, there still exist in the Madras
Presidency a not inconsiderable number of ancient bunds which serve their
intended purpose at the present day as well as ever. Slight mistakes did
occasionally occur, as they ever will till no more dams are wanted, as is
proved by the remains of some works in Ceylon, where the failure was
evidently due to error, possibly due to the instruments being out of
adjustment, as their base is at a higher level than the bed of the stream
at the point where water from the latter was to be diverted to afford the
supply.
Among the most remarkable of these ancient works is the Horra-Bera tank,
the bund of which is between three and four miles in length and from 50
to 70 ft.
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