When a distributary passes through land _Irrigation works

it frequently cuts through the small watercourses which run from the

well to the fields. In such cases, either a syphon or a supplementary

well is provided at Government cost. If several watercourses, all from

the same well, are cut through, it is generally possible to combine them

for the purpose of the crossing. The wishes of the cultivators in this

matter are met as far as possible.

The procedure as regards laying out the line on the ground, digging

trial pits, correcting the line and preparing the estimate are the same

as for the case of a canal.

[Illustration: FIG. 13.]

10. =Best System of Distributaries.=--Let AB (Fig. 13) represent a

portion of a distributary, the irrigation boundary CD being two miles

from AB. In order to irrigate a rectangular plot ACDB, the main and

branch watercourses would be arranged somewhat as shown by the full and

dotted lines respectively. Generally, the whole supply of the main

watercourse would be sent in turn down each branch, the other branches

being then dry. The average length open is AGE. The ends of the branches

lie on a line drawn say 200 feet from the lines BD and DC, since it is

not necessary for the watercourses to extend to the outside edges of the

fields. Within the field there are small field watercourses which

extend to every part of it. By describing three rectangles on AC, making

AB greater than, equal to and less than AC, it can be seen that the

average length of watercourse open is least--relatively to the area of

the block--when AB is equal to AC, i.e., when the block served by the

watercourse is square as in the figure. If AB is 4 times AC, the average

length of watercourse open is increased--relatively to the area of the

block--in about the ratio of 3 to 2. Moderate deviations from a square

are of little consequence.

Suppose two parallel distributaries to be 4 miles apart, each of them

being an average Indian one, say sixteen miles long with a gradient of

one in 4,000, and side slopes of ¹⁄₂ to 1, the bed width and depth of

water at the head being respectively 13·5 feet and 2·9 feet, and at the

tail 3 feet and 1 foot. The discharge of the distributary, with N =

·0225, will be 72 c. ft. per second. The discharge available for the 2

mile strip along one bank will be 36 c. ft. per second. If the duty is

300 acres per c. ft. the area irrigated in this strip will be 10,800

acres, or 1,350 acres for each of the eight squares like ACDB. Each main

watercourse would then have to discharge 4·5 c. ft. per second.

Supposing its gradient to be 1 in 4,000 and its side slopes ¹⁄₂ to 1 and

N to be ·0225, its bed width would be 3 feet and depth of water 1·45

feet. Its wet border would be 6·3 feet, and its average length 5280√2 +

5280 - 200 or 12,546 feet. Its wetted area would be 79,040 square feet,

and the total wetted area of the 16 watercourses--on the two sides of

the distributary--would be 1,264,640 square feet. The wetted border of

the distributary itself is 19·5 feet at the head and 5 feet at the tail,

average 12·25 feet, and its wetted area is 5,280 × 16 × 12·25 or

1,034,880 square feet.

If the distributaries were two miles apart, there would be twice the

number of distributaries, and each square would be one square mile

instead of four. Each watercourse would have to discharge 1·125 c. ft.

per second. It would have a bed width of 2 ft., depth of water ·8 ft.,

wet border 3·8 feet, length 6,173 feet, and wetted area 23,457 feet. The

total wetted area of the 64 water courses would be 1,501,248 square

feet, or 18 per cent. more than before. Each distributary would

discharge 36 c. ft. per second, the bed width and depth at the head

being 10 feet and 2·24 feet, and at the tail 2 feet and ·75 feet. The

wet border at the head and tail would be 14·5 and 3·5 feet, mean 9 feet,

and the wetted area of the two distributaries would be 1,520,640 square

feet or 50 per cent. more than before. Supposing that, in the case of

the larger distributary considered above, the 2-mile square was

considered too large, and that rectangles 1 mile wide were adopted, so

that the watercourses were a mile apart, their number would be doubled

and their length and size reduced. Their total wetted area would not be

greatly affected, but the difference in the wetted areas of the two

small distributaries as compared with the one large one, would be the

same as before. In practice, of course, distributaries are not always

parallel, nor are the blocks of irrigation all squares, and frequently,

owing to peculiarities in the levels of the ground or the features of

the country, or the boundaries of villages, it is necessary to align the

watercourses in a particular manner, or to construct more than one

watercourse where one would otherwise have sufficed, but the above

calculations show in a general way the advantages of large watercourses

and of not placing the distributaries too near together.

It is commonly said that a watercourse discharging more than 4 or 5 c.

ft. per second is objectionable because the cultivators, if there are

too many of them on one watercourse, cannot organize themselves in order

to work it and keep it in order. This matter is much exaggerated. On the

inundation canals of the Punjab a watercourse often discharges 10 c. ft.

per second, and is several miles long and requires heavy clearances, but

the people have no particular difficulty in managing it. Kennedy, a

great authority on questions of irrigation, states that the length of a

watercourse may be three miles. This, if the angle made by a watercourse

with the distributary is 45°, gives rather more than two miles as the

width of the strip to be irrigated.

Suppose that a distributary instead of being two miles from each side of

the irrigated strip, ran along one side of it, and was four miles from

the other side. If the block were square, as before, the side of a

square would be 4 miles, and each watercourse would have to discharge 18

c. ft. per second, which is far too much. The blocks would have to be

rectangles, each being only one mile wide measured parallel to the

distributary. It has been already seen that the length of watercourse in

this case is greater than when the block is square and each side is two

miles. Thus centrality in the alignment of the distributary is an

advantage.

A minor distributary has been defined (CHAPTER II., Art. 3) as being one

discharging not more than 40 c. ft. per second, but the term has come to

be used to designate a branch of a major distributary, and in that sense

it will be used in this article. When the shape of the area commanded by

a distributary is such that watercourses exceeding 2 miles in length

would otherwise be required, one or more minors are often added.

Frequently it is a question whether to let some of the watercourses be

more than two miles long, or to construct a minor and thus shorten the

watercourses to perhaps only one mile. Which method is best has not been

definitely settled. It is known that the loss of water in watercourses

is heavy, but if a minor is added the loss in it has to be considered.

The loss must be high in any channel in which the ratio of wet border to

sectional area is small. The minor also costs money in construction and

in maintenance. On the whole the matter, as far as concerns cost and

loss of water, is, perhaps, almost evenly balanced, but as regards

distribution of the supply a system without minors is preferable. The

off-take of a minor is generally far from the canal, i.e., in a more or

less out-of-the-way place, and it is impossible to see that the

regulation is properly carried out. Irregularities and corruption are

sure to arise. Even if the supply is fairly distributed as between the

minor and the distributary it is almost certain that the regulator, if a

double one, will be manipulated for the illegal benefit of outlets in

the distributary upstream of the bifurcation. There are sure to be some

such outlets not very far distant. In any case each minor adds one, if

not two, to the already very large number of gauges which have to be

entered daily in the sub-divisional officer’s register (CHAPTER III.,

Art. 3), and adds also to the mileage of channel to be inspected and

maintained. These considerations should, in many cases, though of course

not in all, turn the scale against the construction of a minor. At one

time it became usual to construct minors even when watercourses more

than two miles long would not otherwise have resulted. This custom was

condemned some years ago, and is not likely to be re-established. Most

of the difficulties just mentioned can, in the case of a minor which is

not too large, either absolutely or relatively to the main distributary

downstream of the off-take, be got over by making the minor head like a

watercourse outlet, building it up to the proper size, removing the

regulating apparatus and abolishing the reading of the gauge, but in

this case the minor is not likely to be bigger than a large watercourse.

Such minors should not be constructed, and any existing ones should,

after the head has been treated as above, be made over to the people and

considered as watercourses.

11. =Outlets.=--The top of the head and tail walls of an outlet are

level with the F.S. levels in the distributary and watercourse

respectively. The steps in the head wall enable the cultivators to go

down either to stop up the outlet or to remove any obstruction. The

stepping is arranged so as to fall inside the side slope ultimately

proposed. It is usual, in some places, to have the entrance to the

“barrel” of the outlet made of cast iron. The cast iron pieces are made

of various standard sizes. This to some extent prevents the “barrel”

being built to a wrong size. A discrepancy between the size of the

masonry barrel and that of the iron would be noticed, but if the masonry

barrel is built too large the iron head does not always restrict the

discharge. The action is the same as in a “diverging tube” well known in

hydraulics.

For sizes up to about 50 or 60 square inches the barrel should be nearly

square. For larger sizes the height should exceed the width. Up to

about 100 or 120 square inches the width can be kept down to 7 or 8

inches so that an ordinary brick can be laid across to form the roof.

For larger outlets the height can be from 1·5 to 3 times the width, and

the roof can be made of large bricks, concrete blocks or slabs of stone

or of a flat arch of brickwork or by corbelling, but in this last case

there should be two complete courses above the top of the outlet. The

less the width the cheaper the roof, the easier the adjustment of size

and the less the tendency to silt deposit during low supplies. If pipes

are used they should be laid in concrete. If cast iron head pieces are

to be used there should be several sizes of one width and the widths of

the masonry outlets should be made to suit these widths.

A masonry outlet is not generally built till the watercourse has been

sometime in use. The exact position of the outlet should then be so

fixed that the watercourse shall run out straight or with a curve and

should not be crooked.

The width between parapets should be, for a driving road or one to be

made into such, 10 ft. (if the bank is wider, it should be narrowed just

at the outlet site) and for a non-driving road, 8 feet to 3 feet

according to the ultimate width of the bank. Earth backing should be

most carefully put in and rammed, otherwise a breach may occur and the

outlet be destroyed.

Various attempts have been made to provide gates or shutters for

outlets. The chief result has been trouble and increased cost. If

grooves are made and shutters provided, the shutters are soon broken or

lost by the people. Hinged flap shutters are objectionable because they

are often closed by boys or by malicious persons or by neighbours who

wish to increase the supply in their own outlet. The cultivator, when he

wishes to reduce the supply or to close the outlet, can easily do this

by obstructing the orifice with a piece of wood or an earthenware vessel

or a bundle of brushwood or grass.

As regards temporary outlets, wooden outlets if large (unless made of

seasoned wood and therefore costly) are liable to give great trouble.

Water escapes round the outside or through the joints. Pipes may do well

if laid in puddle but are brittle and costly if of large size. The

irrigators may interfere both with wooden outlets and pipes and they are

liable to be displaced or broken. A temporary outlet, if small, can be

made of bricks laid in mud. The joints can be pointed with lime mortar.

When the outlet is made permanent the same bricks are used again. But

all kinds of temporary outlets are liable to give trouble especially in

light or sandy soil. There is much to be said in favour of building

masonry outlets at the first, making a barrel only, _i.e._, omitting the

head and tail walls and taking the chance of having to alter the size.

The alteration is not very expensive. The head and tail walls are built

when the size has been finally settled. The adjustment can be made by

raising or lowering the roof. This should be done over the whole length

of the outlet but lowering can be done temporarily over a length of 3

feet at the tail end of the outlet. This can be done even when the

distributary is in flow. A reduction over a short length at the upstream

end of a barrel does not, as already remarked, necessarily reduce the

discharge much.

On inundation canals the rules regarding outlets have to be modified.

Great numbers of watercourses take off directly from the canals. In such

cases, especially near the head of a canal, the ground to be watered is

often 5 to 8 feet above the canal bed and it is wholly unsuitable to

place the outlet at bed level. The cost of the tail wall would be

excessive. The floor level in such cases must be at about the lowest

probable cleared bed level of the watercourse, say, in order to be safe,

a foot or half a foot below the usual cleared bed of the watercourse, so

that water need never be prevented from entering the watercourse. The

irrigators should be consulted as to the floor level and their wishes be

attended to as far as possible. For lift outlets the floor should be at

the bed level of the canal or distributary. If this bed is to be raised

in the course of remodelling, the floor should be at the old bed level

until the bed has actually been raised, unless there is a weir which

raises the water. It is necessary that lift outlets should work however

small the canal supply may be. In a distributary or small canal, the

head wall should be built up to F.S. level but in a canal with deep

water the head wall should reach up to just above the roof of the outlet

and be submerged in high supplies. The stepping of the head wall should

be set back if the channel is to be widened and should project into the

channel if the channel is to be narrowed. The centre line of the channel

near the outlet site must always be laid down and the outlet built at

right angles to it and also at the correct distance from it.

Occasionally there is a wide berm, say 20 ft. or even 50 ft., between a

channel and its bank. In such a case the outlet should be built to suit

the bank. The long open cut is however objectionable because the people

clear it and heap the spoil in Government land. Sometimes the bank,

especially if it is crooked, can be shifted so as to come close to the

channel at the outlet site. Sometimes the outlets on inundation canals

are large. For outlets of more than 2·5 square feet in area, grooves

should be provided so that the cultivators can use a gate if necessary.

12. =Masonry Works.=--The positions and descriptions of all the masonry

works of a proposed canal or distributary are of course shown on the

longitudinal section of the channel and from this the discharges and

water levels are obtained. The principles of design to be followed[19]

for bridges, weirs, falls, regulators and syphons, are discussed in

_River and Canal Engineering_. It is mentioned that there is no special

reason for making the waterway of a regulator exactly the same as that

of the stream, and that the waterway may be such as to give the maximum

velocity considered desirable, and that the foundations of a bridge

should be made so deep that it will be possible to add a floor, at a

lower level than the bed of the stream--with the upstream and downstream

pitching sloping up to the bed--so as to increase the waterway and so

save pulling down the bridge in case the discharge of the channel is

increased. It remains to consider certain points affecting Irrigation

Canals.

[19] So far as concerns their capacity for dealing with flowing water.

The span of a bridge, where there are no piers, is generally made as

shown by the dotted lines in Figure 14, so that the mean width of

waterway is the same as that of the channel. The arches, in Northern

India, used at one time to be 60° as shown by the upper curved line, but

in recent years arches of 90° as shown by the lower curved line, have

frequently been adopted, the springing of the arch being below the F.S.

level, so that the stream is somewhat contracted. The 90° arch gives a

reduced thickness and height of abutment. It causes increased

disturbance of the water, and this may necessitate more downstream

protection. An advantage of having the springing not lower than the F.S.

level is that this admits of a raising of the F.S. level in case the

channel is remodelled, and this arrangement is still common on

distributaries.

[Illustration: FIG. 14.]

When a fall and bridge are combined, the bridge is placed below the fall

as this gives a lower level for the roadway. The side walls of the fall

are produced downstream to form those of the bridge.

The roads in India are generally unfenced and the banks of canals close

to bridges, on both sides of the canal and both above and below the

bridge, are generally more or less worn down by cattle, which, when

being driven home in the evening and out to graze in the morning, go

down to the stream to drink. In order to prevent this damage the banks

are sometimes pitched, above the bridge as well as below it, but the

cattle generally make a fresh “ghát” further away. The best plan is to

allow a “ghát” on one bank either above or below the bridge and to

protect the other three places.

In the Punjab the widths of roadways between the kerbs and parapets of

bridges respectively have been fixed as follows:--

--------------+----------------+-------------------

KIND OF ROAD.| NEAR TOWNS.[20]|IN THE COUNTRY.[21]

--------------+------+---------+--------+----------

|Kerbs.|Parapets.| Kerbs. | Parapets.

--------------+------+---------+--------+----------

Provincial | 22 | 23·5 | 16 | 17·5

District | 18 | 19·5 | 14 | 15·5

Village | 14 | 15·5 | 8·5 | 10

--------------+------+---------+--------+----------

[20] The figures show the maximum. The general width should be the

same as for neighbouring bridges on the same road.

[21] The parapets should be whitewashed so as to be visible at night.

[Illustration: FIG. 15.]

Fig. 15 shows a head regulator for a distributary. The scale is 10 feet

to an inch. It has a double set of grooves for the insertion of the

planks with which the regulation is effected. Only one set of grooves is

ordinarily used, but when the distributary has to be closed for silt

clearance and all leakage stopped, both sets of grooves can be used and

earth rammed in between the two sets of planks. The floor is shown a

foot lower than the bed of the distributary. This reduces the action of

the water on the floor, and enables the bed of the distributary to be

lowered if ever the occasion for this should arise. This is a good

rule--in spite of the fact that in re-modellings the tendency is for the

beds to be raised--for all regulators or bridges, a raised sill being

added (in regulators) to reduce the length of the needles or the number

of the planks. Such sill should, where needles are to be used, be fairly

wide, especially if regulation is to be done while the masonry is

somewhat new. The distributary shown has a bed width of 10 ft. The span

of the two openings in the head might have been four feet each, but are

actually five feet, and this enables the distributary to be increased in

size at any time. The pitched portion of the channel tapers. Unless

needles are used, instead of horizontal planks, spans are not usually

greater than 5 or 6 feet. Longer spans would give rise to difficulties

in manipulating the planks. Sometimes distributary heads are built skew,

but there is seldom or never any good reason for this. A curve can

always be introduced below the head to give the alignment the desired

direction.[22] The small circles shown on the plan are “bumping posts.”

On the left is shown a portion of the small raised bank at the edge of

the road.

[22] The curve can be quite sharp (see CHAP. I., Art. 2), and can be

made, if necessary, within the length of the pitching.

[Illustration: FIG. 16.]

Figure 16 is a double regulator with needles. The scale is 30 feet to an

inch. The spans are 15 feet. The roadway is on arches, but the

regulating platform on steel beams. The needles are seen at the upstream

sides of the regulators. They are worked from the platforms to which

access is obtained through the gaps in the upstream parapets. The

regulating platform should generally be only just clear of the F.S.

level, and therefore lower than the roadway.

[Illustration: NEEDLE REGULATOR AND BRIDGE.

Needles lying on Bank.

_To face p. 85._]

Frequently the roadway of a bridge or small regulator is carried, not on

arches, but on steel beams. The railings may be of wood or of gas pipe

with the ends plugged, running through angle iron posts. In the case

of such a regulator the roadway is sometimes so light that camels are

not allowed to cross over. This causes unnecessary hardship. Bridges are

not too numerous. If the regulation is done by gates, both road and

platform are carried on arches.

The regulators on inundation canals, and some on perennial canals, are

not strong enough to admit of the flow of water being entirely stopped,

so that the depth of water would be perhaps 10 feet upstream and nil

downstream. This might cause the overturning of the piers, or the

formation of streams under the floor. In such cases a maximum

permissible heading up is decided on. Such orders are, in India, liable

to be lost sight of in course of time, and they are, at least on

inundation canals, where sudden emergencies often occur, hardly

reasonable. An engine driver is not told that he must never entirely

close his throttle valve. Regulators should be so designed that the

water can be completely shut off.

The following remarks show the chief points in favour of needles and

horizontal planks respectively.

_Advantages of Needles._ Needles can be placed or removed by one man.

Needles do not require hooks, etc., which are liable to be broken or

lost.

A needle regulator requires few piers, and is therefore cheap.

Water falling over planks throws a strain on the floor.

Regulation with needles is easy and rapid. A jammed plank, especially

if low down and not horizontal, may give great trouble.

_Advantages of Planks._ Floating rubbish is not liable to collect

above the Regulator because the water flows over the planks.

By means of double grooves and earth filling, leakage can be quite

stopped.

For large works the advantages are generally with needles, but for small

works, _e.g._ distributary heads and shallow water, with planks. Needles

14 feet long are not too long for trained men. Planks are more likely

than needles to arrest rolling sand, and this can be taken into

consideration in designing double regulators. See number 8 of Kennedy’s

rules, Article 5. When planks are used there should be two sets of

grooves. Planks are very suitable for escape heads which have only

occasionally to be opened, earth being filled in between the two sets of

planks.

[Illustration: FIG. 16A]

Regarding notched falls, in the case of small distributaries the notches

are so narrow that they are extremely liable to be obstructed either

accidentally by floating rubbish or wilfully by persons whose outlets

are upstream of them. Weirs are not open to this objection, and are

frequently adopted. There is not the least chance of their causing any

silting worth mentioning. A simple weir if made of the proper height for

the F.S. discharge, will cause a slight heading up with ³⁄₄ths of the

F.S. discharge, and this unfairly benefits any outlets for a

considerable distance upstream of the weir. This difficulty can be got

over by making the weir as in Fig. 16A.

[Illustration: BRIDGE AND NOTCH FALL.

In this case the usual practice of placing the bridge downstream of the

fall has not been followed.

The gauge well is seen on the left bank.

_To face p. 87._]

For cisterns below falls the usual rule for the depth is

K = H + ∛H √D

where H is the depth of water in the upstream reach, and D is the

difference between the upstream and downstream water levels. Another

rule for distributaries is

H + D

K = -----

the length of the cistern being 3 H and its width the bed width of the

channel.

At “incomplete” falls, i.e., where the tail water level is above the

crest, it is not unusual to construct a low-level arch, which forms a

syphon. The object is to allay the surging of the surface water.

The question of skew bridges has been dealt with in Art. 3. Another

question is that of the heights of bridges. Irrigation channels,

especially the smaller ones, are very frequently at a high level, and

bridges have ramps which are expensive to make and to maintain, and are

inconvenient. The lowering of distributary bridges in such cases, so

that they become syphons, or nearly so, has often been advocated and is

frequently desirable. The bed should slope down to the floor and up

again. The heading up can be reduced by giving ample waterway, but it

will not be necessary to do this if there is head to spare. The fall in

the water surface can be recognised and shown on the longitudinal

section. The structure becomes one of the incomplete falls above

described. The crown of the arch can, if desirable, be kept above F.S.

level, so that floating rubbish will not accumulate.

The width between the parapets of a regulator can be 10 feet in the case

of a driving road. It may be less, according to the width of the bank,

in other cases.

The upper layer of the floor of a bridge or regulator is of brick on

edge. Below this there is a layer of brick laid flat, and below this,

concrete of a thickness ranging from ·5 feet to 3 feet. The thicknesses

of piers range from 1·5 to 3 feet.

The bricks used for canal work in Northern India are 10 inches long,

4⁷⁄₈ inches wide, and 2³⁄₄ inches thick. The thicknesses of walls are

about ·83, 1·25, 1·7, 2·1, 2·5 feet, and so on.

The slopes of ramps should be about 3 in 100 for district roads, and 5

in 100 for village roads.

Railings should be provided along the tops of high walls and top of

pitching near to public roads or canal patrol roads. Bumping posts

should be provided for all parapets, and should not be so placed as to

seriously obstruct the roadway.

The quarters for the regulating staff should, when convenient, be in the

fork between the two principal branches. They may be on the bank--with

foundations on pillars carried down to ground level--but not in such a

position as to obstruct the road or any road likely to be made. Rests

consisting of two parallel timbers bolted to blocks of masonry reaching

up a foot from the ground, should be provided for the needles or planks.

The bolt head should be countersunk so as not to damage the needles and

planks when they are hurriedly laid down.

When two or more works are close together they should be made to

conform, and the whole site should be considered with reference to a

neat and suitable arrangement of works, ramps and roadways. If an outlet

is near to a minor or distributary head the parapets of the two should

be in line. If two masonry works of any kind are near together it is

often suitable to pitch the intervening space. If there are outlets or

distributaries on opposite banks they should be exactly opposite each

other. Where a road crosses a bridge or regulator, the bank should be at

the same level as the road, the bank being gradually ramped back to its

original level. The space in front of any quarters should have a slight

slope for drainage, but otherwise be at one level and be connected with

the road or bank by proper ramps. The berm or bank should be made at the

exact level of the top of any pitching or side wall which adjoins it.

Wing walls are frequently made too short, so that the earth at their

ends forms a steep slope and is worn away, and the bank or roadway is

cut into. The walls should extend to such a point that the earth at

their ends cannot assume a slope steeper than the slope of the bank.

It is obvious that for every masonry work there should be a large scale

site plan[23] showing all roads, ramps, and adjoining works, both

existing and proposed roads being shown for some little distance from

the work.

[23] It is, or was until recently, in some parts of India, the custom

to omit the preparation of site plans, and to leave the fixing of the

exact site of a work and the arrangement of ramps and other details to

the judgment of the assistant engineer who was building it. Much

unsightly work resulted. A chief engineer in the Punjab recently

issued some orders on the subject.

For each kind of masonry work there is usually a type design. A few of

its dimensions, which are fixed, are marked on it. The other dimensions

are variable. It would be a great advantage to add to the design a

tabular statement to show how these dimensions should vary under

different circumstances.

[Illustration: FIG. 17.]

[Illustration: FIG. 18.]

13. =Pitching.= The object of pitching upstream of bridges or regulators

or downstream of bridges where there may be little or no scouring

action, may be partly to protect the bank from damage by cattle or wear,

or to prevent sandy sides from falling in. In such cases there may be

pitching of the sides only, and it may be of brick on edge laid dry and

under this one brick flat resting on rammed ballast (Fig. 17).

Downstream of regulators or weirs and downstream of bridges if

contracted or having piers which cause a rush of water, especially if

the soil is soft, the side pitching may be as above, but with the bricks

over one-sixth of the area placed on end and projecting for half their

length. This “roughened pitching” tends somewhat to reduce the eddying.

The bed protection should be solid concrete or blocks of concrete or

masonry. Immediately downstream of regulators or weirs where there is

great disturbance, both side and bed pitching may consist of solid

concrete or of concrete or masonry blocks (Fig. 18).

[Illustration: FIG. 19.]

Three kinds of toe walls are shown in Figures 17, 19 and 20. The kind

shown in Fig. 19 contains, for a given depth below the bed, far more

masonry than the one shown in Fig. 17. It is also liable to be displaced

and broken if scour occurs.

[Illustration: FIG. 20.]

The earth should in all cases be carefully cut to the proper slope, so

that no made earth has to be added. If the slope has already fallen in

too much, well rammed earth should be added. The flat brick and rammed

ballast can be varied as the work proceeds, more being used in soft

places and less in hard.

In some parts of the Punjab, large bricks, the length, breadth, and

thickness being about twice the corresponding dimensions of an ordinary

brick, are made, and are extremely useful and cheap for pitching. Where

the soil is sandy such bricks can be burned without cracking.

Sometimes the curtain wall which runs across the bed at the downstream

end of the pitching is carried into the banks and built up so as to form

a profile wall (Fig. 21). This is not very suitable, because the

pitching of the sides is apt to settle and leave the profile wall

standing out. It is better to lay a row of blocks on the slope. If a

hole tends to form in the bed downstream of the curtain wall, blocks of

masonry or concrete can be laid and left to take up their own positions

(Fig. 22).

[Illustration: FIG. 21.]

[Illustration: FIG. 22.]

When scour of the bed or sides occurs downstream of pitching, it is

sometimes said that any extension of the pitching downstream is followed

by extension of the scour. This may happen if the cross section of the

stream downstream of the pitched section has become greater than the

pitched section. In this case there is eddying, due to abrupt

enlargement of the stream where the pitching ends. The increased width

and lowered bed level (not counting mere local hollows) of the stream

should be adhered to in the pitching. Where the masonry of the regulator

ends and the pitching begins, there will be an abrupt or tapered

enlargement, but the eddies--at very low supplies there may be a

fall--cannot do harm.

This principle of enlarging the pitched cross section can be followed,

even in a new channel, if the soil is light and scour is feared, and for

this reason the matter is mentioned in the present Chapter instead of

in Chapter III. It was once the custom to splay out the sides of a

channel, downstream of a regulator or weir, so as to form a sort of pool

in which the eddies exhausted themselves, but this gives curved banks

and requires extra land and is not a very convenient or neat

arrangement. Where scour of the sides is likely to occur, or has

occurred, immediately downstream of the pitching the latter may be

turned in as shown in Fig. 23.

[Illustration: FIG. 23.]

Pitching has constantly to be replaced or extended owing, generally, to

failure to pitch a sufficient length or to ram well the earth under the

pitching, or to use properly rammed ballast or flat brick, or to give

proper bed protection, or to the use of dry brick pitching when a

stronger kind is needed.

The side slopes of pitching should be 1 to 1. They can be ¹⁄₂ to 1 in

rare cases, _e.g._, when there is no room for 1 to 1, or in continuation

of existing ¹⁄₂ to 1 pitching. No absolute rule can be laid down as to

the length to be pitched, but in a Punjab distributary it is often about

5 times the bed width.

14. =Miscellaneous Items.= On Indian canals the chainage[24] is marked

at every thousand feet. Five thousand feet is called a “canal mile.”

The distance marks are often cast iron slabs, fixed in a cylindrical

block of brickwork about 2·1 feet in diameter and 1·5 feet high, the

upper edge being rounded to a radius of ·4 feet. The wedge-shaped bricks

for these blocks are specially moulded. The iron slab should project

about eight inches and have about a foot embedded in the brickwork.

[24] In India, instead of the simple word “chainage” the term “reduced

distance” is used. It is the distance reduced to a common starting

point as levels are reduced to mean sea level. The expression is

puzzling to non-professionals and new comers.

On a canal having a wide bank the distance mark is put at the outer edge

of the patrol bank, earth being added, if necessary, to increase the

width. On a distributary with a narrow bank the mark should be on the

opposite bank not the patrol bank. To enable the miles to be easily

distinguished the masonry block can be sunk only ·5 foot in the ground,

the others being sunk a foot. In all cases the masonry block rests on a

pillar, 1·7 feet square, of bricks laid in mud, carried down to the

ground level.

Profile walls (Fig. 21, page 92) used occasionally to be built at

frequent intervals along a distributary. They will not prevent scour

occurring, if the stream is tending to scour, unless very close

together. Such walls are of some use as showing whether the channel is

altering, but they are expensive and have to be altered if, as often

happens, the channel is remodelled. It is a much better plan to lay down

blocks--about 1¹⁄₄ foot cubes--of masonry or concrete, along the centre

line at every 500 feet, with their upper faces level with the bed. If

the bed scours they may be displaced but otherwise they are useful not

only for showing what silt, if any, has deposited, but for showing the

centre line of the channel. Without them the centre line is liable to be

altered in silt clearances or berm cuttings. To enable a block to be

readily found and to be replaced in proper position if displaced, there

should be two small concrete pillars exactly opposite to it and

equidistant from it, one on either bank of the channel. Such blocks and

pillars may with advantage be placed at quite short intervals on curves.

The rest houses for the use of officials on tour are generally at

intervals of about 8 to 14 miles. There is generally a rest house near

to a large regulator and frequently there is one near to a small

regulator. This facilitates inspection work and discharge observations

and it saves money, because the house can be looked after by one of the

regulating staff. Not infrequently the house is placed just too far away

from the regulator. Similarly if a rest house is near a railway station

it should be within a quarter of a mile of it--always provided that this

does not bring it too near to villages or huts--and not a mile or more

away as is sometimes the case. It is also a mistake to place a rest

house off the line of channel unless perhaps when it is on a district

road which crosses the channel.

CHAPTER III.

THE WORKING OF A CANAL.

1. =Preliminary Remarks.= A large canal is under a Superintending

Engineer and it often constitutes his sole charge. It consists generally

of three to five “divisions,” each under an Executive Engineer. A

division has two to four subdivisions, each under a Subdivisional

Officer. A subdivision is divided, for purpose of engineering work and

maintenance, into several, generally three or four, sections, each

consisting of some 20 miles of canal and some 40 miles of distributary,

and being in charge of a native overseer or suboverseer, and for

purposes of water distribution and revenue, into a few sections each

having, perhaps, some 30,000 acres of irrigation and being in charge of

a native zilladar. As far as possible the boundaries of divisions and

subdivisions are co-terminous with those of the branches of the canal. A

distributary is always wholly within a subdivision. At every regulator

there is a gauge reader, who, supplied when necessary with permanent

assistants, sees to the regulation of the supply. If there is a

telegraph office at the regulator the telegraph “signaller” may have

charge of the regulation. The zilladar has a staff of some ten or twelve

patwaris, who record in books the fields watered and who are in touch

with the people and know when the demand for water is great, moderate or

small, and for what kind of crops it is needed. In each division there

is generally a Deputy Collector who is a native official, ranking as a

Subdivisional Officer. His duty is to specially supervise the revenue

staff in the whole division. Both he and the Subdivisional Officer have

magisterial powers which are exercised in trying petty cases connected

with the canal.

Along a main canal and its branches there is nearly always a “canal dak”

or system of conveyance of bags containing correspondence for the

officials stationed on the canal or touring along it. Along the main

line, and most of the way down the branches, there is a line of

telegraph for the special use of the canal officials. The telegraph

offices are at the chief regulators, with tapping stations, for the use

of officials on tour, at the rest houses near to which the line runs.

However carefully a canal has been designed, alterations in the channels

from silting and scour soon take place and they go on more or less

without cessation. In a distributary, especially if the gradient has of

necessity been made somewhat flat, there is quite likely to be a deposit

in the upper reach. The deposit is generally greatest at the head and

decreases, in going downstream, at a fairly uniform rate. It may extend

for half-a-mile or less or more. Or a deposit may occur on the sides,

which grow out and contract the channel. This often occurs over a great

length of a distributary or even over the whole of it. Sometimes a

distributary scours its bed, or the sides may fall in somewhat.

Clearances of the silt and cutting of the berms are effected at

intervals. Falling in of the sides may be stopped by means of bushing,

and scour of the bed may be stopped by raising the crest of a fall or by

introducing a weir, but in the meantime the changes cause the discharge

tables for the distributary to become more or less erroneous. In many

cases silt deposits in the upper part of the distributary during the

summer months when the river water is heavily silted and scours away

again in the winter, the régime of the channel being, on the whole,

permanent. The changes which occur in the branches and main canal are

similar to the above and the remedies adopted are similar. On some of

the older canals the scour was so serious that many intermediate weirs

had to be constructed. The remarkable silting in the head reach of the

Sirhind Canal has been described in _River and Canal Engineering_,

Chapter V. The remedy consisted in keeping the gates of the

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.

[Illustration: FIG. 24.]

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

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 |

| +-----+---------+---------+------------+

| +-----+----+----+---------+-----+------+

|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

| +------------+-----+---------+---------+---------

| +------+-----+-----+----+----+----+----+----+----

|Date.| _G._ | _D._| _G._|_G._|_D._|_G._|_D._|_G._|_D._

| |------+-----+-----+----+----+----+----+----+----

| | | | | | | | | |

| 1 | | | | | | | | |

| 2 | | | | | | | | |

| 3 | | | | | | | | |

| * | * | * | * | * | * | * | * | * | *

| 29 | | | | | | | | |

| 30 | | | | | | | | |

| 31 | | | | | | | | |

--------------+-----+------+-----+-----+----+----+----+----+----+----

--------------------+------+-----+-----+----+----+----+----+----+----

--------------------+------+-----+-----+----+----+----+----+----+----

--------------------+------+-----+-----+----+----+----+----+----+----

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

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.

------+------------+------------+---------+------+------------------

+------+-----+------+-----+ to date.| date.|

| For |Up to| For |Up to| | |

------+------+-----+------+-----+---------+------+------------------

Octo- | 3255 | 3255| 31 | 31 | 6510 | 1·0 |

ber | | | | | | |

| | | | | | |

Novem-| 3390 | 6345| 27 | 58 | 9000 | 1·41 |Closed 3 days

ber | | | | | | |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.

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. |

| |--------+--------+---------+--------------------+

Name and | | | |Sectional+----------+---------+

------------+-------+--------+--------+---------+----------+---------+

|1902-03| | | | | |

Name |1903-04| | | | | |

|1904-05| | | | | |

Bank |1905-06| | | | | |

|1906-07| | | | | |

------------+-------+--------+--------+---------+----------+---------+

|1902-03| | | | | |

Name |1903-04| | | | | |

|1904-05| | | | | |

Bank |1905-06| | | | | |

|1906-07| | | | | |

------------+-------+--------+--------+---------+----------+---------+

Total } |1902-03| | | | | |

of } |1903-04| | | | | |

|1904-05| | | | | |

{Village |1905-06| | | | | |

{ Page |1906-07| | | | | |

------------+-------+--------+--------+---------+----------+---------+

Village ..................................

------------+-------+-------------------------------------------------

| | Working of outlet.

| |-------------------------------------------------

| | Area in acres. |

Name and | |----------+--------+-----------------+ Net

of outlet. | |Commanded |Remitted|------+----+-----+per cent of

------------+-------+----------+--------+------+----+-----+-----------

|1902-03| | | | | |

Name |1903-04| | | | | |

|1904-05| | | | | |

Bank |1905-06| | | | | |

|1906-07| | | | | |

------------+-------+----------+--------+-----------------+-----------

|1902-03| | | | | |

Name |1903-04| | | | | |

|1904-05| | | | | |

Bank |1905-06| | | | | |

|1906-07| | | | | |

------------+-------+----------+--------+-----------------+-----------

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

--------+------------+-----------+----+----+----+----+----+----+----

--------+------------+-----------+----+----+----+----+----+----+----

--------+------------+-----------+----+----+----+----+----+----+----

--------+------------+-----------+----+----+----+----+----+----+----

| | | | | | | | |

| | | | | | | | |

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.

[Illustration: FIG. 25.]

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.

If the discharge of a channel is increased, the waterways of bridges may

need increasing. This can often be done (Chapter II., Art. 12) by making

a floor at a low level. Or the waterway may be allowed to remain small,

the floor being added at the bed level and the bridge then becoming an

incomplete fall, (page 87). The fall in the water surface, though small,

can be recognised and shown on the longitudinal section.

In remodelling schemes, the longitudinal section should give all

possible information. It should show not only the levels of bed and

banks, but the F.S. levels (in blue figures) above and below all falls

or regulators, and the levels of floors and waterways of bridges. The

plan should show all watercourses and the “chaks” or areas assigned to

them.[34] On each chak the actual average irrigation can be shown in

blue figures and the proposed irrigation in red. The “draw-off” for each

proposed outlet can then be shown on the longitudinal section. The area

actually irrigated, as shown on the map, should in each case be the

mean of at least three years, and if possible of five years. The number

of years should be mentioned in a note on the map. Cross-sections of

channels should always be drawn to natural scale, and not with the

horizontal scale differing from the vertical.

[34] The field maps mentioned on page 101 are prepared to a very large

scale and show all watercourses. The maps should always be corrected

up to date by the patwaris. The chak maps which are on a smaller

scale--say 4 inches to the mile--can thus be kept correct.

7. =Remodelling of outlets.= When a channel is remodelled, the

remodelling of the outlets may consist in alterations of the number or

sites or in alterations of their sizes.

Regarding the former, a map should be prepared showing all watercourses,

chaks and contours.[35] On this map new lines for the watercourses can

be shown, the principles enunciated in Chapter II., Art. 9, being

generally followed, but in such a way as to utilise existing

watercourses and outlets as far as possible. The work often consists in

the abolition of a certain number of watercourses, when these are too

close together and run parallel to one another. There may, however, be

little gain in amalgamating two such watercourses if they serve two

different villages. There is nothing to prevent the people from dividing

the watercourse into two as soon as it gets away from the canal, and

they are likely to do this in many cases. When one branch has a flatter

slope than the other it would lose command if it took off further down.

The people on the steeper branch might not agree to using the flatter

one because of silt trouble, or increased height of embankment. In a new

project it is not difficult to get the people to do what is needed, but

when once irrigation has become established it is often difficult to get

suitable changes made. The advantages of amalgamating watercourses,

though appreciable, have been a good deal exaggerated. The chief

advantage is gained by reduction in the sizes of outlets. Then, however

many branches the watercourse may have, they can only run in turns and

not all together. It may happen that two watercourses, though taking off

near one another, run in different directions and that the chaks are of

suitable shapes and sizes. In such a case the only advantage of

amalgamating is that it saves an outlet in the canal bank. No saving in

the length of watercourse will be effected because there will be a

bifurcation as soon as the watercourse leaves the canal boundary. If

both outlets are of suitable design and proper size or require only

slight alteration, both can remain but otherwise amalgamation can be

effected. In some cases amalgamation might give a discharge greater than

that usually allowed for an outlet but this need form no obstacle. The

chief reason for limiting the discharge is the alleged inability of the

farmers to manage a large channel. This matter is exaggerated as already

stated (page 74). In the case under consideration it obviously makes no

difference whether there are two watercourses each discharging 5 c. ft.

per second, or one discharging 10 c. ft. per second, and immediately

dividing into two. Very small watercourses should, when possible, be

joined to others but if there is no other near enough they must

generally remain, however small they may be.

[35] In small remodelling schemes the lines of existing watercourses

show how the country slopes, and a contour plan is not a necessity.

Regarding the alterations in sizes of outlets, whether or not there are

alterations in their number and position, information as to the actual

duties on the watercourses should be obtained. The discharge of the

watercourses should be observed several times and added up and checked

with the discharge of the distributary. The areas irrigated are known

from the irrigation register. If the duties are abnormal the causes can

be gone into, and a judgement can be formed as to how far they will

remain in existence, and whether any watercourse is often kept closed.

If so the outlet is too large. The duties, modified so far as may seem

desirable, can be used for calculating the sizes of the remodelled

outlets. But alterations of the sizes after a year or two years’ working

will probably be necessary. The above procedure is also applicable to a

case where the old watercourses had no masonry heads but were merely

open cuts as on some inundation canals.

A common case is that in which the channel is not remodelled--or at

least its water level remains very much as before--but merely the

outlets are altered in number, position or size, or in any or all of

these. If the land irrigated by an outlet is high, the irrigation may be

far short of what was expected, and the size of the outlet may have to

be increased or its site shifted, generally upstream. This is often done

at the request of the people, and at their expense.[36]

[36] On some of the more modern canals the people are not allowed to

pay for outlets, so that no question of ownership can arise.

Old outlets should always be removed when superseded by others.

Otherwise they are apt to be reopened or claims set up regarding them.

Near the tail of a channel the discharge of an outlet may be an

appreciable fraction of that of the channel. In such a case the

adjustment of the size of the outlet, and that of the channel or of any

weir or fall in the channel, should be considered together, the

irrigation on the outlet and that on the channel downstream of it being

compared. And similarly as to the sizes of any two or more tail outlets.

Such outlets are sometimes left without masonry heads on the ground that

this injures no one. It may injure an outlet upstream of them by drawing

down the water. Tail outlets often need constructing or reducing in size

to raise the water level in the reach upstream of them.

Whenever the size of an old outlet is altered the design should be

altered if unsuitable. The parapets should be brought into proper line,

the roadway corrected, the floor level adjusted and any splayed wing

walls abolished. If the outlet is skew it should be made square. All

this should also be done to all old outlets or heads of minors even if

the sizes are correct, whenever remodelling of outlets on any channel is

undertaken.[37]

[37] Wherever an outlet is built or altered, a template, made to the

exact size of barrel required, should be supplied to the subordinate

in charge of the work.

It was stated in Chapter II. that the construction of masonry outlets on

a distributary is not usually a final settlement of the matter. In many

cases a proper proportion of water does not reach the tail. Even in such

a case matters have occasionally been left alone, or the old and

pernicious system of closing the upper outlets has been resorted to. In

such circumstances the irrigation of a group of tail villages will be

found to be less than that of a group higher up, the people to some

extent acquiescing in the old idea that a tail village must be a

sufferer. Government, or at least the Irrigation Department, has no

particular direct interest in the matter. The total area irrigated, will

probably be very much the same in any case. But an engineer who takes an

interest in this part of his work will not allow matters to remain long

in the state described. He will, of his own accord, adjust the outlets

and equalise, as far as possible, the irrigated percentages. The people

will disturb matters to some extent by enlarging watercourses, but there

is a limit to this and it can be met by an occasional reduction of an

outlet. A distributary, when once its outlets have been carefully

adjusted, attains to something approaching perfection in its working.

Any excess in the supply is taken partly by the upper outlets but part

of it gets to the tail. Similarly any deficiency in the supply is

distributed over the channel. The outlets which have a poor command and

small head are most affected in either case. On the whole they do not

lose or gain more than the others. The working of such a distributary

causes great satisfaction to the engineer and not the least ingredient

in this is the knowledge that he has wholly destroyed the power of his

native subordinate.

In an inundation canal division in the Punjab, some dozen

distributaries, varying in length from 5 to 28 miles, and with

discharges ranging up to 300 c. feet per second, were dealt with as

above in one season. The engineer in charge being specially desirous

that sufficient water should reach the tails, reduced the sizes of some

outlets too much. When an outlet of 1 or 2 sq. feet has to be reduced to

a small fraction of its size it is not easy to say what the fraction

shall be. Water reached the tails of all the channels in sufficient

quantity, in some cases in rather more quantity than was necessary.

When the irrigation register was examined, it was found that the general

results were entirely satisfactory. In a small proportion of cases

outlets had irrigated too little and had to be re-enlarged somewhat.

After a second season hardly any changes were needed. When any silt

clearance or berm-cutting seemed necessary the irrigation register again

came into play. If, for instance the tail outlets, as a whole, were

receiving too little water, enlargement of the upstream reaches was

effected with consequent lowering of the water level there.

In the case above described the channels flowed for only five months in

the year. Some of them silted a good deal but as this silting was

roughly the same every year, it did not greatly affect the question of

outlet sizes. On a perennial distributary of which the head reach silts

during part of the year and scours during the other part, a proper

distribution of supply by adjustment of outlet sizes alone may be more

difficult. If the silt was frequently cleared, this would cause needless

expense and interference with irrigation. In cases where the

distributary is not run constantly, something can be done by attending

to the regulation. When there is silt in the head reach, the discharge

can be reduced and the period of flow proportionately increased. The

lowered water level reduces the supplies of the upper outlets, and

increases the discharges of those lower down. Moreover the periodical

silting and scour are not always serious. Also it is not essential that

the supply to each watercourse should be exactly the same every year.

There are always good and bad seasons. It is sufficient if a watercourse

is not allowed to suffer on the whole, and is never allowed to suffer

much. There is no doubt that it is possible to deal satisfactorily in

the above manner with very many distributaries. It is frequently

reported that “difficulty is experienced in getting water to the tail.”

This is owing to timidity in reducing the sizes of outlets. The suitable

plan is to reduce them to such an extent as to cause a proper supply to

reach the tail and then, if necessary to enlarge some. It has been

already remarked that only a short length of the barrel need be altered.

The cost of this is very small. The real difficulty in the case is not

the impossibility of securing good results, but the impracticability, in

many cases, of securing the constant attention which the procedure

demands.[38]

[38] See also Chapter V. Art 3.

8. =Miscellaneous Items.= At the headworks of a canal there is a

permanent staff of men who work the gates and look after the works. They

assist in discharge observations and in reading the gauges, and they may

have to take soundings in the river to see what changes are taking

place. Some one is on watch day and night and reads the gauges at

frequent intervals. The officer in charge occasionally inspects the

works at night without notice. Detailed rules regarding the above

matters, and any others that are necessary owing to special local

conditions, are drawn up. Sometimes there is difficulty in getting the

staff to attend properly to the regulation of the supply in the canal at

night. Probably some “tell-tale” watches would be useful. They would at

least show the times at which the men concerned went to the gauges or

other points.

At the headworks, and at all important regulators, a stock of concrete

blocks should be kept ready for the execution of any urgent repairs.

Regarding the ordinary maintenance work on the channels, details are

given in Appendices B and C. Appendix D, reprinted from _Punjab Rivers

and Works_, contains rules for watching and protecting any banks or

embankments which require it.

Silt clearances and berm cutting of channels have been mentioned in Art.

1. Special attention should be given to the accurate ranging of the

centre line. Otherwise the channel may become crooked. The great defect

in the earthwork ordinarily met with in the banks of canals and

distributaries is that the clods are not broken. In consequence of this

new banks are extremely liable to breach, and much trouble and expense

result. Sometimes a dam is thrown across a new distributary, and the

channel upstream of it is gradually filled with water, the bank being

watched and leakages made good. The dam is then shifted to a place

further down. In this way the banks are consolidated.

When a distributary is closed for silt clearance or other work, if the

head regulator has planks and a double set of grooves, it is possible to

stop all leakage by filling in earth between the two sets of planks and

ramming it, but otherwise it is necessary to construct an earthen dam

just below the regulator. Upstream of the dam the water, owing to the

leakage through the planks, gates or needles, rises to the same level as

the water in the canal. Native subordinates have a remarkable aptitude

for allowing such dams to break while the work in the distributary is in

progress or before it is measured. Now and then the dam is wilfully cut.

The remedy is to make the dam of proper strength--the top should be 8

feet wide and a foot above the water,--and to have it watched day and

night.

At a bend in a channel there is often a silt bank next the convex bank,

and a hollow near the concave bank. The average bed level is probably

very much the same as in the straight reaches. Removal of the silt bank

is unnecessary, and if removed it quickly forms again.

Any length of channel in which the depth of silt to be cleared is small,

say ·50 foot in a large channel and ·40 foot in a small one, should not

be cleared, provided its length is considerable (say 1,000 feet), and

that it is not close to (say within 3,000 or 2,000 feet from) the head

of the channel. Estimates should be prepared accordingly, the shallow

digging being struck out. Clearing a small depth of silt merely gives

contractors a chance of cheating by scraping the bed.

If the watercourses at the tail of a distributary are silted, the people

should be pressed to clear them. Otherwise there will be heading up of

the water of the distributary, and silt deposit may result.

When a channel is scoured, any regulator in it can be kept partly closed

so as to reduce the surface slope in the reach upstream of the regulator

and encourage the deposit of silt. A table should, in such cases, be

drawn up giving the gauge readings to be maintained at the tail of the

reach corresponding to given readings at the head.

Various methods of protecting banks are described in _River and Canal

Engineering_, Chapter VI. The growing of plants on the inner slopes of

channels whose sides fall in, needs special attention. Some remarks on

this are given in _Punjab Rivers and Works_, Chapter II., Art. 3. A

specification for bushing is given in Appendix E of this volume.

When a distributary passes through land which is irrigated from wells,