Canal....................................Distributary........................
From....................................To.....................................
Name of Village.Commanded
Culturable
Area (Acres)		Detail.Net Areas Irrigated in Areas.
1902-031903-041904-051905-061906-071907-081908-09
Kharif
Rabi
Total
Per cent of
Culturable
Kharif
Rabi
Total
Per cent of
Culturable
Kharif
Rabi
Total
Per cent of
Culturable
Total

The percentages of culturable commanded area irrigated by different outlets will, as already explained, always show discrepancies. Any special causes of low percentages, e.g. a large proportion of rice, can be briefly noted in the register.

On inundation canals, and some others, the alignment and chainage are liable to undergo alteration. In such cases it is best to adhere to the original chainage until all the alterations in alignment have been carried out.

5. Distribution of Supply.

The question how the supply of a canal is to be distributed when it is less than the demand, is not always very simple. Suppose that the main canal, after perhaps giving off several distributaries, divides, at one place, into three branches, A, B, and C, whose full supply discharges are respectively 2,500, 2,000 and 1,500 c. ft. per second. Suppose that the total discharge reaching the trifurcation is expected to be, when at the lowest during the crop, only 2,200 c. ft. per second, instead of 6,000. It would be possible, supposing the discharge tables to be fairly accurate, to keep all the channels running with discharges proportionate to their full supplies, but this would not be suitable. The water levels would not be high enough to enable full supplies to be got into the distributaries, or at least into some of them. Moreover, the running of low supplies causes much loss by absorption. The plan usually adopted is to give each channel full supply, or nearly full supply, in turn, and for such a number of days that the turn of each branch will recur about once a fortnight, that being a suitable period having regard to the exigencies of crops, and having the advantage that the turn of each branch comes on a particular day of the week, so that everyone concerned, and especially the irrigating community, can remember and understand it. [Table V.] shows how the turns in the above case can be arranged. The figures show the discharges.

TABLE V.

Day.ABC
12,200
22,200
32,200
42,200
52,200
6 2,000200
7 2,000200
8 2,000200
9 2,000200
10 2,000200
11700 1,500
12700 1,500
13700 1,500
14700 1,500
Total13,80010,0007,000
Correct
discharge
according
to Full Supply.		12,80010,3007,700

The orders given to the gauge readers in these cases are simple, namely to give each branch full supply in turn, and to send the rest of the water down the channel next on the list.

The number of days allotted to the larger branches are greater than to the smallest because this will probably be simplest in the end, and also because the number of distributaries on a larger branch is likely to be greater, and the allotment to the distributaries is thus facilitated somewhat. Each branch receives water in one period of consecutive days. Any splitting up of the turn would be highly objectionable. It would cause waste of water, and would give rise to much difficulty in redistributing the supply among its distributaries. Each branch receives its residuum turn before it receives its full supply turn. The advantage of this is that water is not let into the channel suddenly. The total supplies of A, B and C are in the ratio of 13·8, 10, and 7, and not, as they should be 12·8, 10·3, and 7·7, but no closer approximation can be got. If the number of days of full supply allotted to each branch is changed, or if the residuum from C is given to B, instead of A, the relative total discharges differ still more from what they should be.

If now the total supply is supposed to be increased to 2,700 c. ft. per second, the discharges are as shown in [table VI.]