Irrigation works

by E. S. Bellasis

2. Gauges and Regulation.

—In every canal, branch and major or minor distributary there is a “head gauge” below the head regulator. At every double regulator there is a gauge in each branch and also an upstream gauge. These gauges are used for the regulation of the supply. The zeros of the gauges are at the bed levels. Tables are prepared showing the discharges corresponding to each gauge reading—except in the case of upstream gauges—at intervals of ·1 foot.

The question often arises whether it is necessary to have a gauge near the tail of a distributary. If the outlets have not been properly adjusted and if water does not reach the tail in proper quantity, a tail gauge is absolutely essential and its readings should be carefully watched by the Sub-divisional Officer. To take no action until complaints arise or until the irrigation returns at the end of the crop show that some one has suffered, is not correct. When it is known that sufficient water always reaches the tail, a tail gauge is not necessary.

There may be intermediate gauges on a canal or branch or distributary. For convenience of reading they are usually at places where a distributary or minor takes off or where there is a rest house. They serve to show whether the water level at that place alters while that at other places is stationary, and thus give indications of any changes occurring in the channel. The number of such intermediate gauges should be rigorously kept down. In fact hardly any are necessary. The gauge register which the Subdivisional Officer has to inspect daily, is, in any case, voluminous enough.

At a double regulator it is never necessary, except as a very temporary arrangement in case of an accident, to partially close both channels at once. One or the other should be fully open. The upstream gauge reading shows whether this rule is being adhered to. If the bed levels of all three channels at the regulator are the same, the reading on one or other of the downstream gauges should be about the same—for the fall in the water passing through an open regulator is generally negligible—as that of the upstream gauge. In other cases the difference in the bed levels has to be taken into account.

Immediately downstream of the off-take of a channel, there is, unless the water flows in without any appreciable fall, much oscillation of the water. For this reason the gauge is frequently fixed some 500 feet down the channel. This is anything but a good arrangement. The gauge-reader’s quarters are close to the off-take and he will not keep going down to the gauge. Moreover an official coming along the main channel cannot see the gauge. The gauge should be close to the head and in a gauge well where oscillations of the water are reduced to very small amounts. The upstream gauge requires no well.[25]

[25] For further details as to gauges see [Appendix G].

All gauges should be observed daily, in the morning, and the reports sent by canal dak, post or wire at the earliest possible moment. This should be rigidly enforced. The register should be posted and laid before the Subdivisional Officer daily with the least possible delay. It is only in this way that the Subdivisional Officer can keep proper control of the water, and detect irregularities. Sometimes trouble arises owing to the gauge reports not coming in regularly. The suboverseer can be made responsible for seeing to this matter as regards all the gauge readers in his section. Gauge readers often reduce the supply in a branch or distributary at night for fear of a rise occurring in the night and causing a breach. This is to save themselves the trouble of watching at night. They are also bribed to tamper with the supply and run more or less in any channel or keep up the supply for a longer or shorter time. All regulation should be rigorously checked by the suboverseer, zilladar and Subdivisional Officer. Irregularities can be speedily detected if proper steps are taken such as going to the regulator unexpectedly. The watermarks on the banks can also be seen. If any man is found to have delayed entering a gauge reading in his book or despatching the gauge report it is evidence of an intention to deceive. The suboverseer or zilladar should be required to enter in his note-book all the checks he makes and the Subdivisional Officer should see the entries and take suitable steps.

There was formerly a general order in the Punjab that the Subdivisional Officer should write the gauge register with his own hand. Such an order is not now considered necessary nor has the Subdivisional Officer, now-a-days, time to comply with it. The register should however be written by the clerk carefully and neatly and not be made over to anyone else.

The regulation should usually be so effected that rushes of water in any portion of the channel are avoided, but if scour occurs in a particular part of the channel it may be necessary to try and obtain slack water there. Until it is proved by experience that they are unnecessary, soundings should be taken periodically downstream of large works. When a branch or escape is closed the leakage should be carefully stopped. The necessary materials should be always kept ready in sufficient quantity.