(iii) In dry years, that is, 1 in 4, it will be necessary to attain a duty almost exactly the same as that now obtaining on the Upper Bari Doab Canal.
(iv) That an exceptionally dry year might occur once in 14 years, when the supply would be 10 per cent. short of that required by the average Upper Bari Doab Canal standard of requirements: such exceptional cases should be met by remissions, which will be far preferable to wasting the good supplies of 13 years out of 14.
(v) That the occasional occurrence of dry years makes it inadvisable to attempt a greater proportion of rabi than half of the annual irrigation.”
3. Remarks.
The Report on the Project estimates gives, for each tract, remarks on its soil, rainfall, height of subsoil water, circumstances as to existing irrigation from wells or small canals and liability to floods. On a consideration of these matters the decision as to the particular parts of the tracts which are to be irrigated and the areas which are, in the rabi, to receive only restricted irrigation, depends.[50]
[50] It is not unusual, in tracts where the level of the subsoil water is high, say within 15 feet of the surface, to have some “kharif distributaries.” These are closed in the rabi. This tends to prevent water-logging of the soil. In the rabi the people lift water from wells. There may also be kharif distributaries in dry tracts if there is no water to spare in the rabi.
In calculating the sizes of the canals, N in Kutter’s co-efficient was taken at ·020. In sharp curves the bed is paved on the side next the concave bank. In high embankments where the soil is sandy the best material is used as a core wall. The torrent works on the Upper Jhelum Canal have been mentioned in River and Canal Engineering, Chapter XII.
Regarding the effect of the new canals on the inundation canals which take off, lower down, from the Chenab below its confluence with the Jhelum, it has for long been the policy to gradually shift the heads of these canals upstream in order to obtain better supplies, or rather to counteract the effect of the abstraction of water for the recently constructed Lower Chenab and Lower Jhelum Canals. Any such abstraction of water has not much effect on the floods, but it has much effect in April and May, when the rivers have not fully risen, and in September, when they are falling.
In order to estimate the effect on the water level of the Chenab—below its junction with the Jhelum—it was necessary to observe discharges of the river, not only in the winter when it is low, but in the summer when it is high. The depth of the water was in some places 40 feet, and the stream 2,000 feet wide. Fortunately the Subdivisional Officer was a native of India and did not much mind the sun. A discharge curve (River and Canal Engineering, Chapter III. Art. 5,) having been prepared, it was possible to construct a diagram with periods of time as the abscissas, the ordinates representing the average known gauge readings on the different dates and another set of ordinates representing the probable discharges. By deducting the discharges which it was intended that the new perennial canals should draw off, it was possible to draw fresh ordinates representing the diminished river discharges and the reduced river gauge readings corresponding to them. It was found that the water level would be lowered by about 1·3 feet in April and May, and by about 1·5 feet in September. It was, however, shown that by shifting the heads of the inundation canals upstream—the gradients of the canals being flatter than that of the river—the effect of the lowering of the water level could, as heretofore, be nullified.