Regarding the working out of delta month by month, not only are discharges more or less doubtful, but the area irrigated is seldom correct till near the end of the crop. However, the figures, towards the end of a crop, may be useful. If delta on any distributary is higher than is usual on that distributary, it may be desirable, if the supply in the whole canal is short, to reduce the supply to that distributary somewhat, but this remedy can be properly applied after the end of the crop by altering the turns ([Art. 5]). Any steps in the direction of altering outlets can only be taken after the end of the crop. Admitting, however, that the working out of delta during the crop is useful, it can be done by adding up the gauge readings for the month and taking the average reading and the discharge corresponding to it. This is not quite the same as the average of the daily discharges, but the difference is small, and there would be a wholesale and most salutary saving in clerical work. All the columns headed D could be omitted. The handiness and compactness of the register would be vastly increased. The discharges are only approximately known, and refinements of procedure are unnecessary. The correction of the discharge table, by means of observed discharges, once a month, can of course be effected without booking the daily discharges.[27]
[27] There should, in any case, be a special place in the gauge register for showing the discharge tables, with a note of the discharge observations from which the table was framed or in consequence of which it was altered.
Supposing the columns D to be retained the calculations of delta can be made as shown in [table II.] the form being printed in the gauge book. To facilitate the adding up of the discharges a line can be left blank in table I. after each ten days, and the total for the ten days shown on it. If the column D is not retained, the gauge readings can be added up. The discharge corresponding to the mean gauge reading of the month, multiplied by the number of days the distributary was in flow, gives the figure to be entered in column 2 of [table II.]
The final working out of delta crop by crop is of course of the greatest value. The point which needs attention is, as already remarked, greater accuracy in the discharges. For reasons which have already been given ([Chap. I., Art. 5], and [Chap. II., Art. 9]) the values of delta on different distributaries will never be the same, but the causes of high values can always be investigated and, to some extent, remedied.
TABLE II.—CALCULATION OF DELTA FOR RABI, 1912-13, NANGAL DISTRIBUTARY.
| Month. | Total of discharges. | No. of days in flow. | Irrigated area up to date. | Delta up to date. | Remarks. | |||
|---|---|---|---|---|---|---|---|---|
| For month. | Up to date. | For month. | Up to date. | |||||
| Acres | Feet | |||||||
| October | 3255 | 3255 | 31 | 31 | 6510 | 1 | ·0 | |
| November | 3390 | 6345 | 27 | 58 | 9000 | 1 | ·41 | Closed 3 days because of breach. |
4. Registers of Irrigation and Outlets.
It is obvious that a Subdivisional Officer cannot look properly into matters connected with the working of his channels unless he has, ready to hand, a register showing, crop by crop, the area irrigated by each distributary and each outlet and keeps it posted up to date. In 1888 the Chief Engineer of the Punjab Irrigation directed that each Subdivisional Officer should keep up English registers of irrigation by villages. The order was for years lost sight of. The matter has lately, in view of certain recent occurrences on a large perennial canal, again come to notice, and this most essential factor in the working of a canal is, it is believed, receiving attention.
As to the precise form which an irrigation register should take, opinions and practices differ somewhat. In all cases the net irrigated areas should be shown—kharif, rabi, and total—and the total remitted area. The areas remitted for kharif and rabi separately may or may not be shown. The net percentage of the commanded culturable area irrigated—total of the two crops—can be shown in red ink and is most useful.[28] It enables the general state of affairs on any outlet to be seen at a glance and shows how it compares with other outlets and with the whole distributary.
[28] Provided that the culturable commanded area is properly shown and is not made to include jungles or other tracts which were never intended to be irrigated.