Irrigation works : $b the principles on which their design and working should be based, with special details relating to Indian canals and some proposed improvementsBellasis, E. S. (Edward Skelton)
Science
Irrigation works : $b the principles on which their design and working should be based, with special details relating to Indian canals and some proposed improvements
Bellasis, E. S. (Edward Skelton)
Canals; Irrigation
enormous differences in duty may occur. There is no way of arriving at
the proper size for an outlet except trial. Observations of the
discharges of the outlets are of very limited use. The discharge may
vary according to the particular fields being irrigated. Observations of
discharges will be useful in cases where the people complain, or when
the discharge is obviously much greater or much less than intended and
will in such cases enable temporary adjustments to be made, but by
placing a dam in a watercourse and turning the water on to a high field
near its head the people can make it appear that the discharge is only a
fraction of what it should be.
On any distributary there are generally some watercourses which have a
poor command, the head at the outlet being, say, ·1 ft. or even less.
Probably the irrigation is a good deal less than it should be. In such
cases the rules may be set aside and a liberal size of outlet given. The
size may be 2 or 3 times the calculated size. There is no harm in this.
The irrigation cannot increase much. Similar cases frequently occur on
inundation canals especially near the heads of canals or distributaries.
The construction of masonry outlets on a distributary is not usually a
final settlement of the matter. Further adjustments become necessary.
This matter will be dealt with in CHAPTER III.
On the older canals little or insufficient attention was given to the
question of the sizes of outlets. The sizes were far too great and, as
long as all the outlets in a distributary remained open, water could not
reach the tail. The distributary used to be divided into two or three
reaches and the outlets in the upstream reaches used to be closed
periodically. The closures had to be effected through the agency of
native subordinates and the system gave rise to corruption on a colossal
scale. The tail villages never obtained anything like their proper share
of water. The upper villages were over-watered and the soil was often
water-logged and damaged. Moreover, even if all concerned had the best
intentions, it was impossible to stop all leakage in the closed outlets,
except by making earthen dams in the watercourses, and great waste of
water resulted from this.
Public-domain text, read in full here on John Shaqi.
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