Chapter V: The remedy consisted in keeping the gates of the (1)

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under-sluices properly closed so that a pond was formed in which the river silt deposited. When necessary the canal is closed, the sluices opened, and the silt scoured away. For a plan of the headworks see fig. 24.

In working a canal, it is necessary to arrange so that the water sent down any channel is as nearly as possible in accordance with the demand. The zilladar supplies the Subdivisional Officer, every week or ten days, with an “indent” showing how much water is required in each distributary and the Subdivisional Officer makes indents on the subdivision next above. The officer in charge of the headworks thus knows what the demand is. When it is more than the supply available, the water is dealt out to the various divisions according to rules approved of by the Superintending Engineer of the canal.

Every gauge-reader has to be given definite instructions as to the gauge reading to be maintained, until further orders, in each distributary. At the places where the large branches take off, the gauge reader is instructed what gauge to maintain in each. In the event of too much water arriving, he turns the surplus into the escape if there is one. If there is no escape he has usually to raise the gauge readings of the branches by equal amounts. By means of the telegraph, adjustment is promptly effected at the headworks.

It has already been mentioned that rain may cause an abrupt reduction in, or even cessation of the demand for water. At the same time it increases the actual supply. Rain, or the signs of rain, in any part of a canal system ought always to be reported to the other parts. Owing to changes in the channels, to fluctuation in the water level of the river, especially during the night, to rain or to changes in the temperature and moisture of the air and to lack of continuous attention on the part of the gauge reader, particularly at night, there is a constant, though perhaps small, fluctuation in the water level in all parts of a canal.

It may happen that--owing to enlargement of the channels by scour, or to other causes--the channels of a canal system are able to carry more water than was intended. In such cases the channels are usually run with as much as they can carry. This may give a lavish supply and a lowered duty, but it increases the irrigated area. To restrict the supply would cause loss of revenue. Sometimes however, it is restricted to prevent water-logging of the soil. The proper procedure is to extend the canal to other tracts.

In India the farmers pay for the water, not according to the volume used, but according to the area irrigated. Different rates per acre are charged for different kinds of crops according to the varying amounts of water which they are known to require. Sugarcane, which is sown in the spring and stands for nearly a year before being cut, thus extending over the whole of the kharif and most of the rabi, is assessed at the highest rate. Next comes rice which crop, though only four or five months elapse between its sowing and reaping, requires a great quantity of water. Gardens which receive water all the year round also pay a high rate. Other kharif crops are cotton and millet. The chief rabi crops are wheat, barley and “gram.”

Every field irrigated is booked by a patwari who is provided with a “field map” and “field book” for each village (perhaps 6 or 8) in his beat. The map enables him to recognise at a glance the field in which he is standing. It has a number in the map and, by referring to this number in the field book, he finds the area of the field. The patwari is also provided with a “field register” in which he books each field which is watered, showing its area and the kind of crop grown, the date of booking and the name of the owner and tenant. He goes about entering up all new irrigation and his proceedings are subjected to rigorous check by the zilladar and Deputy Collector, and also by the engineering staff. At the end of the crop the entries are abstracted into a “demand statement” in which all the fields cultivated by one person are brought together and, the proper rates being applied to them, the sum payable by this person is arrived at. The demand statement goes to the Collector of the district, who levies the money and pays it into the Treasury to the credit of the canal concerned. There is a special charge for any land watered in an “unauthorised manner.” This includes taking water when it was another man’s turn, or taking it from an outlet which has been wilfully enlarged or--in some districts--from another man’s outlet even with his consent. The sizes of the outlets are carefully apportioned to the land allotted to them and the area which they irrigate is constantly being looked into in order to see if the size is correct or needs altering. If a man borrows water from another outlet such borrowing may or may not come to light but in any case confusion as to outlet sizes results.

The water rates charged for ordinary authorised irrigation are decidedly low. In one district there was a case in which a man, being unable to get as much water as he needed from his own outlet, took water for some fields, by permission, from a neighbour’s outlet. This being found out he was charged for those fields at double the usual rate. He continued regularly to use the water and to pay the double rate. There were several cases of this kind in that one district.

Since payment for the water is not made according to the volume used, the cultivators are more or less careless and wasteful in using it. As a rule they over-water the land and frequently damage or spoil it by water-logging. They do not always keep in proper order the banks of the watercourses. The banks often breach and water escapes. Any area thus flooded is charged for if it is seen by an official. The engineers have power to close such a watercourse until it is put in order, but this would cause loss of revenue and is not often done. The real remedy for all this is, as already stated, rigid restriction of the supply. The people will then learn--they are already learning--to use water more economically.

When the crop in any field or part of a field fails to come to maturity, the water rate on it is remitted. The failed area is known, in the Punjab, as “kharába.” On some canals the failed areas are liable to be large and an irrigation register, in order to be complete, has to show them or, what is the same thing, to show both the gross and the net areas, the latter being the area left after deducting the kharába or remitted area.

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.

3. =Gauge Readings and Discharges.= For the head gauge of each distributary and for certain gauges in the canals, discharge tables, based on actual observations, are prepared. If changes occur in the upper part of a channel, the discharge corresponding to a given gauge reading is altered. One remedy for this is to have a second gauge downstream of the “silt wedge” or scoured or narrowed reach. The indents are then made out with reference to the second gauge, but any slight adjustments due to fluctuation in the water level of the canal, are effected by means of the head gauge. Unless the zilladar and Subdivisional Officer are on the alert, the gauge reader is likely to evade going to the lower gauge every morning, and to enter fictitious readings for it, inferring them from the readings of the head gauge. If there are any outlets between the two gauges, their discharge has to be observed or estimated and added to the discharge of the distributary as entered in the table corresponding to the readings on the second gauge. The above system can be worked with advantage in cases where the distributary bifurcates two or three miles from its off-take. The men in charge of the two regulators can work together, one of them or an assistant, going daily from one regulator to the other and back.

Usually, however, the vitiating of the discharge table at the head gauge has to be faced, and the table to be constantly corrected. It is impossible to frame beforehand any rule or formula which would give a certain correction for a certain depth of silt deposit. Moreover, there might or might not be a contraction of the channel due to deposit on the sides. The usual plan is to observe a discharge some time during each month. If the result is in excess of the tabular discharge, all the discharges for that month are increased in the same proportion. They can be booked according to the table and totalled, and the correction applied to the total.

Discharges of canals and branches at their heads or at the boundaries of divisions, are observed by the Subdivisional Officer about once a month. Discharges of distributaries are observed about once a month, usually by zilladars. They are also to some extent observed by the Subdivisional Officer, but much is left to his discretion. Delta is worked out for each distributary month by month, and also, of course, for each crop. Thus a general duty “at distributary heads” can be obtained, and may be used in new projects[26] instead of the duty at the canal head, allowance being made for the water lost by absorption in the canal and branches.

[26] See CHAP. IV., Art. 2.

It cannot be said that these important figures are obtained as carefully as they could be. If the Subdivisional Officer personally observed the discharge at each distributary head, even every other month, the reliability of the results would be much increased. In addition to this the discharges of canals and branches at the boundaries of subdivisions should be observed and the results compared with the distributary discharges, so as to show the loss by absorption. At first grave discrepancies among the results would be found, but they would be reduced as the causes of error became known. For the method of investigating the causes of discrepant discharges see _River and Canal Engineering_, CHAP. III., Art. 5.

A specimen of a Subdivisional Officer’s gauge register is given in table I. The zilladar keeps a similar register. The columns headed G contain the gauge readings, those headed D the discharges. Until some years ago there were no columns for discharges. The daily discharges of the canal and of the branches at their heads--and at intermediate points if they were at the boundaries of divisions--were entered in the Executive Engineer’s office and the duty was worked out at the end of each crop. The zilladar merely indented for a certain gauge reading at the distributary head, and the Subdivisional Officer could tell pretty nearly what gauge reading he required in the canal at the beginning of his subdivision. Since the year 1900 or thereabouts, the zilladars have been required to learn a good deal about discharges. They have to know how to observe the discharge of a distributary, and to learn how the discharge of an outlet varies with the head or difference between the upstream and downstream water levels. They are supposed to indent for certain discharges, and not merely for certain gauge readings. All this knowledge is useful to the zilladars and tends to increase their efficiency, but a practice of constantly thinking in discharges instead of in gauge readings is unnecessary. If the channels were of all sorts of sizes matters would be different. Actually the size of a channel is apportioned to its work, and the proportion of its full supply which it is carrying at any moment is easily grasped by means of gauge readings alone.

TABLE I--GAUGE AND DISCHARGE REGISTER.

--------------+-----+---------------------------------------
October, 1912.| | Main Line, Upper Bari Doab Canal.
| +-------------------------+------------+
| | Tibri Regulator | Dhariwal |
| +-----+---------+---------+------------+
| |Above| Main | Kasur | Nangal |
| | | Canal | Branch |Distributary|
| +-----+----+----+---------+-----+------+
|Date.| _G._|_G._|_D._|_G._|_D._| _G._| _D._ |
| |-----+----+----+----+----+-----+------+
| | | | | | | | |
| | | | | | | | |
| 1 | | | | | | 4·0| 100 |
| 2 | | | | | | 4·0| 100 |
| 3 | | | | | | 4·0| 100 |
| * | * | * | * | * | * | * | * |
| 29 | | | | | | 4·2| 110 |
| 30 | | | | | | 4·2| 110 |
| 31 | | | | | | 4·2| 110 |
--------------+-----+-----+----+----+----+----+-----|------+
Total | | | | | |127·1| 3255 |
--------------------+-----+----+----+----+----+-----|------+
No. of days in flow | | | | | | 31 | 31 |
--------------------+-----+----+----+----+----+-----+------+
Average | | | | | | 4·1| 105 |
--------------------+-----+----+----+----+----+-----+------+

--------------+-----+------------------------------------------------
October, 1912.| | Main Line, Upper Bari Doab Canal.
| +------------+-----------------------------------
| | Kunjar | Aliwal Regulator
| +------------+-----+---------+---------+---------
| | Kaler |Above|Amritsar | Lahore |Escape
| |Distributary| | Branch | Branch |
| +------+-----+-----+----+----+----+----+----+----
|Date.| _G._ | _D._| _G._|_G._|_D._|_G._|_D._|_G._|_D._
| |------+-----+-----+----+----+----+----+----+----
| | | | | | | | | |
| | | | | | | | | |
| 1 | | | | | | | | |
| 2 | | | | | | | | |
| 3 | | | | | | | | |
| * | * | * | * | * | * | * | * | * | *
| 29 | | | | | | | | |
| 30 | | | | | | | | |
| 31 | | | | | | | | |
--------------+-----+------+-----+-----+----+----+----+----+----+----
Total | | | | | | | | |
--------------------+------+-----+-----+----+----+----+----+----+----
No. of days in flow | | | | | | | | |
--------------------+------+-----+-----+----+----+----+----+----+----
Average | | | | | | | | |
--------------------+------+-----+-----+----+----+----+----+----+----

As regards the weekly indents, the dealing with discharges instead of gauge readings is of little practical value. The zilladar merely knows that on some outlets the demand is great, on others moderate, and he judges that the distributary needs say, 4 feet of water, its full supply gauge being 5 feet. He cannot tell how many cubic feet each outlet requires. If he is required to indent in cubic feet per second (he is not always required to do this) he probably gets at the discharge from the gauge reading, and not the gauge reading from the discharge. As regards the general indent made by the Subdivisional Officer, the same remarks apply. He can probably tell what gauge he requires without going into discharges.

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.

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.

Besides the irrigation figures it is necessary to record for each outlet its chainage, size of barrel[29] and commanded culturable area. In the case of a distributary which has been working for years, and on which the outlets are undergoing few alterations, it may be suitable to record the above items in a separate “outlet register,” and to give in the irrigation register a reference to the page of the outlet register. But even in such a case alterations will have to be made from time to time in the outlet register and there is great danger of its becoming spoilt, imperfect or unintelligible. In the case of a distributary on which the outlets are undergoing frequent changes, the items under consideration should be shown crop by crop, and also the material of the outlet--wood or masonry--and the width and mean height of the barrel. In no other way can the working of the outlet be properly followed and understood. It is probable that this procedure is the best in every case, _i.e._, even when the alterations made are not frequent. By arranging the register as shown in table III. the repetition of the entries, when they undergo no alteration, is avoided, only dots having to be made.

[29] The sizes of the outlets should be measured by the suboverseer
and some checked by the Subdivisional Officer and the correct
sectional area, as actually built, entered.

The specimen shows only two outlets on a page, and covers five years, but three outlets can easily be shown on a large page, and the period can be seven years. If there are more than three outlets in the village, the lowest part of the page shows the total of the page instead of the total of the village, and the other outlets are shown on the next page, the grand total for the village coming at the foot.

TABLE III.--REGISTER BY OUTLETS AND VILLAGES.

Distributary ..................................
------------+-------+------------------------------------------------+
| | Information regarding outlet. |
| |--------+--------+---------+--------------------+
| | | | |Dimensions of barrel|
Name and | | | |Sectional+----------+---------+
description| Year |Chainage|Material| area of | | |
of outlet. | | | | barrel. | Width | Height |
| | | |(minimum)| | |
------------+-------+--------+--------+---------+----------+---------+
Register no.| | | | | | |
|1902-03| | | | | |
Name |1903-04| | | | | |
|1904-05| | | | | |
Bank |1905-06| | | | | |
|1906-07| | | | | |
Flow or lift| | | | | | |
------------+-------+--------+--------+---------+----------+---------+
Register no.| | | | | | |
|1902-03| | | | | |
Name |1903-04| | | | | |
|1904-05| | | | | |
Bank |1905-06| | | | | |
|1906-07| | | | | |
Flow or lift| | | | | | |
------------+-------+--------+--------+---------+----------+---------+
Total } |1902-03| | | | | |
of } |1903-04| | | | | |
|1904-05| | | | | |
{Village |1905-06| | | | | |
{ Page |1906-07| | | | | |
------------+-------+--------+--------+---------+----------+---------+

Village ..................................
------------+-------+-------------------------------------------------
| | Working of outlet.
| |-------------------------------------------------
| | Area in acres. |
Name and | |----------+--------+-----------------+ Net
description| Year | | | Net irrigated |irrigated,
of outlet. | |Commanded |Remitted|------+----+-----+per cent of
| |culturable| |Kharif|Rabi|Total|culturable.
------------+-------+----------+--------+------+----+-----+-----------
Register no.| | | | | | |
|1902-03| | | | | |
Name |1903-04| | | | | |
|1904-05| | | | | |
Bank |1905-06| | | | | |
|1906-07| | | | | |
Flow or lift| | | | | | |
------------+-------+----------+--------+-----------------+-----------
Register no.| | | | | | |
|1902-03| | | | | |
Name |1903-04| | | | | |
|1904-05| | | | | |
Bank |1905-06| | | | | |
|1906-07| | | | | |
Flow or lift| | | | | | |
------------+-------+----------+--------+-----------------+-----------
Total } |1902-03| | | | | |
of } |1903-04| | | | | |
|1904-05| | | | | |
{Village |1905-06| | | | | |
{ Page |1906-07| | | | | |
------------+-------+----------+--------+-----------------+-----------

All the outlets of the uppermost village on the distributary should be entered, first, even though some of them may be downstream of, and bear serial numbers lower than, the outlets of the next village. When one outlet irrigates two or three villages the irrigation of the separate villages can be entered on one page in the places usually allotted to outlets, and the lowest part of the page can show the total for the outlet, the necessary changes in the headings, etc. being made. If any of the villages has other outlets these will appear on another page and the total for the village can also be shown.

The village totals should be posted into a second register prepared somewhat as shown in table IV. and totalled. The totals show the irrigation for the whole distributary.[30] If necessary the failed areas can be shown in the register in red ink. If any village is irrigated from two or more distributaries, each portion of the village should be dealt with as if it was a separate village.

[30] Very long channels, e.g. inundation canals from which direct
irrigation takes place, can be divided into reaches and the irrigation
of the reaches dealt with as if they were separate channels. A reach
should generally end at a bifurcation or stopdam.

In all registers some blank spaces should be left for the insertion of new outlets or new villages. The number of pages to be left will depend on local circumstances, which should be considered. In case figures are supplied by the revenue authorities and deal only with whole villages, the details obtained by the canal staff should always be added up and checked with them. Similarly the commanded culturable areas for the outlets and villages should be added up and checked with the known total for the distributary.

TABLE IV.--ABSTRACT OF IRRIGATION BY VILLAGES AND CHANNELS.

Canal...................... Distributary..............

From....................... To........................
--------+------------+-----------+----------------------------------
Name of |Commanded | | Net Areas Irrigated in Acres.
Village.|Culturable | Detail. +----+----+----+----+----+----+----
|Area (Acres)| |1902|1903|1904|1905|1906|1907|1908
| | | -03| -04| -05| -06| -07| -08| -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. | A | B | C
---------+------+------+------
1 | 2,200| |
2 | 2,200| |
3 | 2,200| |
4 | 2,200| |
5 | 2,200| |
6 | | 2,000| 200
7 | | 2,000| 200
8 | | 2,000| 200
9 | | 2,000| 200
10 | | 2,000| 200
11 | 700| | 1,500
12 | 700| | 1,500
13 | 700| | 1,500
14 | 700| | 1,500
---------+------+------+------
Total |13,800|10,000| 7,000
| | |
Correct | | |
discharge|12,800|10,300| 7,700
according| | |
to Full | | |
Supply. | | |
---------+------+------+------

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.

TABLE VI.

----------+-------+-------+-----
DAY. | A | B | C
----------+-------+-------+-----
1 | 2,500 | 200 |
2 | 2,500 | 200 |
3 | 2,500 | 200 |
4 | 2,500 | 200 |
5 | 2,500 | 200 |
6 | | 2,000 | 700
7 | | 2,000 | 700
8 | | 2,000 | 700
9 | | 2,000 | 700
10 | | 2,000 | 700
11 | 1,200 | |1,500
12 | 1,200 | |1,500
13 | 1,200 | |1,500
14 | 1,200 | |1,500
----------+-------+-------+-----
Total |17,300 |11,000 |9,500
| | |
Correct | | |
Discharge.|15,700 |12,600 |9,500
----------+-------+-------+-----

Considering both the above tables, A always receives more water than its share, while B and C on the whole receive too little. Considering table V. by itself, matters might, perhaps, be set right by altering the total number of days from 14 to 13 or 12, but this, besides being somewhat objectionable for the reason already given, might not improve matters when table VI. came into operation. It is desirable to avoid frequent changes or complicated rules. It is objectionable to make any turn consist of other than a whole number of days. The shifting of the regulator gates is begun at sunrise, a time when officials are about and can see what is happening. All gauges are read early in the morning, and those at regulators are read after the regulation has been done and the flow has become steady. If any regulation were done in the evening, the entry in the gauge register of that day would convey a wrong impression, and the discharge would be incorrectly booked. Moreover, any system of regularly booking evening as well as morning gauges leads to swelling of the already voluminous gauge register.

The best method of adjusting matters is to make slight alterations in the full supply gauges. Suppose the normal full supplies in all three branches to be 6 feet. When table VI. is in operation the full supply of A can be reduced to about 5·8 feet. This would give, during the first 5 days, less water to A and more to B, and there is the further advantage that a very small supply, 200 c. ft. per second, is not run in any branch. As regards table V., branch A never receives full supply. This is a rare case.[31] If it were safe, as it might be, to run slightly more than full supply in C, this could be done, and it would increase the supply in C during the last four days and reduce that in A. Otherwise a certain gauge would have to be fixed for A which would give it less than 2,200 c. ft. per second during the first 5 days, and the balance would go to branch B. Similarly, the gauge of B could be slightly reduced, and this would increase the balance going to C. The orders given to the gauge reader are, as before, to send the full supply down one channel, and the balance to the next. The only additional procedure necessary is to inform the gauge reader from time to time what the full supply gauges are. In any case such information has probably to be conveyed to him at times because the channels undergo changes, and the discharge corresponding to a given gauge also changes.

[31] The total discharge, 2,200 c. ft. per second, assumed, is very
low compared with the full supply of 6,000 c. ft. per second.

When the discharge of the canal exceeds 3,500 c. ft. per second there is, when B and C are receiving water, a second residuum, which goes to A. Tables can be worked out for several discharges of the main canal, but it is the minimum discharge which is the most important factor in the case. The minimum discharge, or something very near it, generally lasts through about half the crop, and it is when the supply is at a minimum that care and justice in the distribution are most needed.

The chief objection to the arrangements above described is that the surplus to be sent down one channel or another is sometimes so small that it must be to a great extent wasted. The best means of preventing this is to have the discharge tables, including one for the main canal at some point higher up than the trifurcation, constantly corrected. In that case, it is known under what circumstances a small surplus will occur, and the orders can be modified so as to prevent its occurrence. The orders will of course be more complicated, and will have to be dealt with by an engineer and not a gauge reader.

The turns, once satisfactorily arranged, may go on for years without alteration. They may require altering if any branch is found, in the course of time, to be doing worse than or better than the others, though the correction can probably be made by altering the full supply gauge.

The turns of the branches having been arranged, it remains to settle those of the distributaries. The total available discharge being, as before, assumed to be rather more than one-third of the full supply discharge, each distributary taking off from the main canal, where it is not possible or not desirable to regulate the height of the water level in the canal, can be run with full supply for four or five days out of each fortnight, and then closed. Whether it be four days or five may often depend on special circumstances such as whether the distributary is doing well or otherwise. If necessary the full supply can be adjusted. When the canal supply increases the four or five days can be increased.

The same principle can be adopted for any distributary whose off-take is in the upper part of a branch, _i.e._, where the branch is many times larger than the distributary, and where it is not possible or not desirable to regulate the water level of the branch. For a distributary further down the branch, the turns of branch and distributary can be arranged as explained above for a canal bifurcation. The orders given to the gauge reader are, as before, to give the channel whose turn it is, full supply and to send the balance down the other channel. When the turn of distributary is over it becomes the turn of the branch. The distributary would not be closed if this would cause the full supply in the branch to be exceeded. Care must be taken that every distributary receives full supply during part of the time when the branch is receiving full supply. If its turn came only when the branch was receiving a residuum supply, or rather when the residuum supply was reaching the distributary off-take--for in the case of a distributary whose off-take is far down a long branch the two things are not the same--it might, in the event of the supply in the main canal falling exceptionally low, receive no water at all.

The time taken by a rise in travelling down a canal is very much the same as that taken by a fall and each takes effect more or less gradually. When a branch receives, at any point, a temporary increase in its supply, owing to the closure of a distributary for, say, three days, there will be a rise lasting for three days at a point further down. The rise will take some time to come to its height, and some time to die away. There will be about three days from the commencement of the rise to the commencement of the fall, or from the end of the rise to the end of the fall. If, either in the main canal or in a branch, there is any distributary into which full supply cannot be got, its turn can be increased accordingly. Owing to the shortness of the turns, and to allowance having to be made for the time occupied by rises and falls in travelling down the branch, the fixing of the turns for distributaries near the tail of the branch requires a good deal of consideration. Matters are facilitated by making a sketch (Fig. 25) in which the widths of the channels, as drawn, are roughly in proportion to the full supply discharges. If 14 copies of the sketch are made the arrangements for each day can be shown on them, full supply being shown black and residuum hatched. Distributaries would be shown as well as the main channels.

The irrigation registers of course show how the irrigation of the different channels is going on from year to year and if changes in the turns become necessary they can be effected.

After the water has entered the watercourses the canal officials have nothing to do with its distribution. The people arrange among themselves a system of turns, each person taking the water for a certain number of “pahars”--a pahar is a watch of three hours--or fractions of a pahar. The zilladar can however be called in by any person who has a dispute with his neighbour. If the matter is not settled the person aggrieved can lodge a formal complaint and a canal officer then tries the case, and if necessary punishes the offender.

In former days it was usual, in some places, for no regular turns to be fixed for the distributaries, orders being issued regarding them from time to time. The weak point about any such plan is that in the event of the controlling officer delaying, owing to any accident, to issue an order, no one knows what to do. Orders were also sometimes issued to zilladars giving them discretionary powers in distribution. No one would now issue such orders. The essential principle is to remove power from the hands of the subordinates. The working of the main channels by turns and the construction of outlets of such a size that they never require closure, has resulted--in places where such matters are attended to--in the absolute destruction of such power.[32] The only way in which a zilladar can injure anyone is to say that water is not in demand. This would however result in damaging the whole of the villages in his charge. He is not likely to do this.

[32] In the printed form lately in use in the Punjab for reports on
zilladars, one of the questions asked is whether “his arrangements”
for the distribution of water are satisfactory, as if that was still
considered to be the zilladar’s business.

In case the supply is wholly or partially interrupted owing to a breach or an accident at the headworks, or other cause, one particular branch or distributary may lose its turn or part of it. If its loss is not great it may be best to allow the turns to take their usual course, but otherwise they should be temporarily altered in such a way as to compensate the channels which have suffered.

On inundation canals the water at a regulator is sometimes headed up,--all branches being partially closed--in order to give more water to outlets in the upstream reach. There are even some regulators--or rather stop-dams--constructed solely for this purpose at places where there is no bifurcation of the canal or distributary. Any such heading up should be planned out beforehand and days for it fixed, and also the gauge reading. If the water, without any heading up, rises to the needful height on the gauge, nothing has to be done. There are also places on inundation canals where the land is high and is only irrigable during floods. At such places it is usual, on some canals, to allow the people to make cuts in the bank when the water attains a certain height. Owing to the high level of the country, nothing in the nature of a breach can occur. In one canal division where the above arrangement was in force, the people used to send applications to the Executive Engineer for leave to cut the banks. This resulted in much delay. A list was prepared showing exactly where the banks might be cut, the people were informed and the formalities were much reduced.

6. =Extensions and Remodellings.= An existing canal or distributary may need remodelling for various reasons, and in various degrees. If the velocity is too high and the bed has scoured, or the sides have fallen in, it may be necessary to raise the crests of falls, or to construct intermediate weirs, or to widen the channel and reduce the depth. If the command is not good it may be necessary to regrade the channel. If silt deposit occurs, the cross-section of the channel may have to be altered, to give a better relation between D and V. If there is surplus water, extensions or enlargements of channels may be desirable and these can sometimes be undertaken to a moderate extent merely by restricting a somewhat too lavish supply to existing distributaries. If the water level is dangerously high it may have to be lowered, or the banks raised and strengthened. Sometimes it is desirable to cut off bends either to shorten the channel and gain command or because the bends are sharp and cause falling in of the banks or, if numerous, silting. In all cases the general principles are the same as for entirely new projects, but certain details require consideration.

The distributaries of the older canals were constructed before Kennedy’s laws regarding silting were known, and it has been necessary to remodel many of them. In some cases the gradient was wrong, in others the cross-section.[33] In some cases a distributary ran in rather low ground, and it was proposed to abandon it and construct a new one on high ground. It was however pointed out by Kennedy (_Punjab Irrigation Paper No. 10_, “Remodelling of Distributaries on old Canals,”) that irrigation had become established along the course of the distributary, that most of it would remain there and that a new alignment would result in increased length of watercourses. Such distributaries have therefore been allowed to remain very much as they were.

[33] The difficulty of reducing the size of a channel which is too
large is well known and has been discussed in _River and Canal
Engineering_, Chapter VIII. It is there explained that a moderate
reduction of width can be effected by “bushing,” but that for great
reductions, groynes or training walls are necessary. When the bed of a
distributary is too low it has been suggested that it could be raised
by filling in earth in each alternate length of 500 feet, and leaving
the rest to silt, but this would be expensive.

Remodelling should not be considered piecemeal, but regard should be had to the whole channel. When a distributary is remodelled the outlets should of course be dealt with as well as the channel. The chief thing to consider is not whether the channel as it exists is exactly as it was originally designed to be, but how it is doing its work and what kind of alteration it needs. Even when a simple silt clearance or berm cutting of a channel has to be undertaken, the work need not always consist in blindly restoring the channel to its original condition. It may be both feasible and desirable to remodel it to a slight extent, lowering the water for instance in reaches where the outlets draw off very good supplies and thus benefiting less fortunate reaches lower down.

The irrigation boundaries of the extended or remodelled channel should as far as possible follow drainages, but these are not always important or pronounced. The actual irrigation boundaries should be shown and also those of any neighbouring channels of other canals, and any suitable adjustments should be made.

Regarding the percentage of area to be irrigated, it has already been stated that one canal or distributary irrigates a far higher percentage than another. Generally when there is a high percentage in any tract, it is undesirable to cut it down unless it has very recently sprung up to the detriment of other tracts. In some remodelling projects a uniform percentage is taken on the whole area including both new and old irrigation. This plan is suitable when the percentage of old irrigation is not very high. In other cases the old irrigation to be provided for may be taken as the maximum area actually irrigated, a little being perhaps added for extensions. If the irrigation of considerable areas of jungle tracts is contemplated and if these consist of numerous small patches, a further percentage can be added for them. If there are large jungle tracts they can of course be dealt with separately and any suitable percentage adopted for them. The percentage for each portion of a remodelling project is not necessarily the same.

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