--------+------------+-----------+----+----+----+----+----+----+---- | | | | | | | | | 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.