292
molehworth’s pocket-book
= I inch of water.
= 1815 cubic feet.
= 130,000 „ ,,
— '12 inch.
Irrigation in India—continued.
In moist districts the following allowance is
made for rice—
Per day of 24 hours = inch of water.
» >. — 1210 cubic feet per acre.
Or per crop .. . = 87,000 cube feet „
In some parts it is usual to allow for waste, and
eo to assume—
Per day of 24 hours .
” » ■
Or per crop..........
Common grain per day
>- = 436 cube feet.
In Central India, to allow for evaporation, the
storage room is from 200,000 to 250,000 cubic feet
per acre.
The discharge of channels isfrequently calculated
at • 02 cubic foot per second ; this is equivalent to
nearly J inch per day. In some cases • 03 is allowed.
A proportion for channels sometimes adopted is
D = Depth in feet, B = Breadth at bottom in feet.
A = Area in square feet.
D — 's/. This proportion gives
B = 2 D, with slopes of 1 to I.
= 1 j D, with slopes of 1| to 1.
And a mean hydraulic depth of
•62, with slopes of 1 to 1.
•59, ,, „ IJtol.
The velocity in feet per second should not be
less than 2 feet per second, nor more than 3f feet
per second, unless the material through which the
channel is excavated be very hard. Large channels
with turbid water require the higher velocity to
prevent silting.