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Title: Irrigation works
        the principles on which their design and working should be based, with special details relating to Indian canals and some proposed improvements

Author: E. S. Bellasis

Release date: December 3, 2017 [eBook #56113]
                Most recently updated: October 23, 2024

Language: English

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*** START OF THE PROJECT GUTENBERG EBOOK IRRIGATION WORKS ***

  Transcriber’s Notes:

  Text between _underscores_ and =equal signs= represent text printed in
  italics and bold face respectively; ^{text} represents superscript
  text; [·1] represents ·1 with a bar above. Small capitals have been
  transcribed as ALL CAPITALS.

  More Transcriber’s Notes may be found at the end of this text.




IRRIGATION WORKS


  _By the Same Author_

  RIVER AND CANAL ENGINEERING. The Characteristics of Open Flowing
  Streams, and the principles and methods to be followed in dealing with
  them. 72 illustrations, x + 220 pp., 8vo (1913).

  =8/6= net.

  PUNJAB RIVERS AND WORKS. Second Edition. 47 illustrations, viii + 64
  pp., folio (1912).

  =8/-= net.

  HYDRAULICS WITH WORKING TABLES. Second Edition. 160 illustrations, xii
  + 311 pp., 8vo (1911).

  =12/-= net.

  THE SUCTION CAUSED BY SHIPS. Explained in Popular Language. 2 plates,
  26 pp., 8vo, sewed (1912).

  =1/-= net.

  E. & F. N. SPON, LTD., LONDON


[Illustration: BRIDGE ON AN INDIAN CANAL.

_Frontispiece._]




  IRRIGATION WORKS

  THE PRINCIPLES ON WHICH THEIR DESIGN
  AND WORKING SHOULD BE BASED, WITH
  SPECIAL DETAILS RELATING TO
  INDIAN CANALS
  AND SOME PROPOSED IMPROVEMENTS

  BY

  E. S. BELLASIS, M.INST.C.E.

  RECENTLY SUPERINTENDING ENGINEER IN THE IRRIGATION BRANCH OF
  THE PUBLIC WORKS DEPARTMENT OF INDIA

  37 Illustrations

  [Illustration]

  London
  E. & F. N. SPON, LTD., 57 HAYMARKET, S.W.

  New York
  SPON & CHAMBERLAIN, 123 LIBERTY STREET

  1913




CONTENTS


                                                        PAGE
  PREFACE                                                vii


  CHAPTER I
  INTRODUCTION

  ARTICLE

  1. Preliminary Remarks                                   1
  2. General Principles of Canal Design                    2
  3. Information concerning Canals                        11
  4. Losses of Water                                      16
  5. Duty of Water                                        21
  6. Sketch of a Project                                  26


  CHAPTER II
  THE DESIGNING OF A CANAL

  1. Headworks                                            30
  2. The Contour Map                                      36
  3. Alignments and Discharges                            37
  4. Remarks on Distributaries                            45
  5. Design of Canal and Branches                         47
  6. Banks and Roads                                      53
  7. Trial Lines                                          58
  8. Final Line and Estimate                              59
  9. Design of a Distributary                             60
  10. Best System of Distributaries                       71
  11. Outlets                                             76
  12. Masonry Works                                       80
  13. Pitching                                            90
  14. Miscellaneous Items                                 93


  CHAPTER III
  THE WORKING OF A CANAL

  1. Preliminary Remarks                                  96
  2. Gauges and Regulators                               103
  3. Gauge Readings and Discharges                       106
  4. Registers of Irrigation and Outlets                 113
  5. Distribution of Supply                              118
  6. Extensions and Remodellings                         127
  7. Remodelling of Outlets                              131
  8. Miscellaneous Items                                 137


  CHAPTER IV
  THE PUNJAB TRIPLE CANAL PROJECT

  1. General Description                                 144
  2. Areas and Discharges                                147
  3. Remarks                                             156


  CHAPTER V
  PROPOSED IMPROVEMENTS IN IRRIGATION CANALS

  1. Preliminary Remarks                                 158
  2. Reduction of Losses in the Channels                 159
  3. Modules                                             162


  APPENDICES

  A. Divide Wall on Lower Chenab Canal                   169
  B. Specification for Maintenance of Channels           171
  C. Specification for Maintenance of Masonry Works      174
  D. Watching and Protecting Banks and Embankments       175
  E. Specification for Bushing                           178
  F. Escapes                                             180
  G. Gauges                                              183
  H. Gibb’s Module                                       186
  K. Kennedy’s Gauge Outlet                              193

  INDEX                                                  196




PREFACE


When _River and Canal Engineering_ was written it was decided to omit
Irrigation works and to deal with them separately because the subject
interests chiefly specialists.

The present book deals with the principles which govern the design and
management of Irrigation works, and it discusses the Canals of Northern
India--the largest and best in the world--in detail.

Some years ago a number of rules for designing distributaries were
framed, at the request of the Punjab Government, by the late Colonel S.
L. Jacob, C.I.E., R.E., and comments on these rules were obtained from
many experienced engineers and recorded. The author has had the
advantage of reading all these opinions. Generally the weight of opinion
on any point agrees with what most experienced engineers would suggest,
and direct conflicts of opinion scarcely occur. Important papers have
been printed by the Punjab Irrigation Branch on Losses of Water and the
Design of Distributaries, on the great Triple Canal Project, on Gibb’s
Module, on Kennedy’s Gauge Outlet, and on the Lining of Watercourses.
These papers are not always accessible to engineers, and the chief
points of interest in them are not, in most cases, discernible at a
glance. Such points have been extracted and are given in this book.

  E. S. B.

  CHELTENHAM, _May_ 20_th_, 1913.




IRRIGATION WORKS.




CHAPTER I.

INTRODUCTION


1. =Preliminary Remarks.=--The largest irrigation canals are fed from
perennial rivers. When the canal flows throughout the year it is called
a “Perennial Canal.” Chief among these are the canals of India and
particularly those of Northern India, some of which have bed widths
ranging up to 300 feet, depths of water up to 11 feet and discharges up
to 10,000 c. ft. per second. Other large canals as for instance many of
those in Scinde, Egypt and the Punjab, though fed from perennial rivers,
flow only when the rivers are high. These are called “Inundation
Canals.” Many canals, generally of moderate or small size, in other
countries and notably in the Western States of America, in Italy, Spain,
France and South Africa, are fed from rivers and great numbers of small
canals from reservoirs in which streams or rain-water have been
impounded. Sometimes water for irrigation is pumped from wells and
conveyed in small canals. In Australia a good deal of irrigation is
effected from artesian wells. Irrigation works on a considerable scale
are being undertaken in Mexico and the Argentine. In this book,
irrigation works of various countries are referred to and to some extent
described, but the perennial canal of Northern India, with its
distributaries, is the type taken as a basis for the description of the
principles and methods which should be adopted in the design, working
and improvement of irrigation channels and it is to be understood that
such a canal is being referred to where the context does not indicate
the contrary. Any reader who is concerned with irrigation in some other
part of the world will be able to judge for himself how far these
principles and methods require modification. The branches and
distributaries--all of which are dealt with--of a large perennial canal
cover all possible sizes.

CHAPTER II. of this book deals with the design of canals and CHAPTER
III. with the working of canals but as the two subjects are to some
extent interdependent, they will both be dealt with in a preliminary
manner in the remaining articles of the present Chapter. CHAPTER IV.
describes the Punjab Triple Canal Project.[1] CHAPTER V. deals with
certain proposed improvements in the working of canals.

  [1] The latest example of canal design.


2. =General Principles of Canal Design.=--The head of a canal has to be
so high up the river that, when the canal is suitably graded, the water
level will come out high enough to irrigate the tract of land concerned.
If a river has a general slope of a foot per mile and if the adjoining
country has the same slope and is a foot higher than the water level of
the river, and if a canal is made at a very acute angle with the river,
with a slope of half a foot per mile, the water level about two miles
from the canal head will be level with the ground.

The headworks of the canal consist of a weir--which may be provided with
sluices--across the river, and a head “regulator,” provided with gates,
for the canal. There are however many canals, those for instance of the
inundation canal class, which have no works in the river and these may
go dry when the river is low. They usually have a regulator to prevent
too much water from going down the canal during floods. If a canal is
fed from a reservoir the headworks consist simply of a sluice or
sluices.

A canal must be so designed as to bring the water to within reasonable
distance of every part of the area to be irrigated. Unless the area is
small or narrow the canal must have “branches” and “distributaries.” A
general sketch of a large canal is given in Fig. 1. On a large canal,
irrigation is not usually done directly from the canal and branches. It
is all done from the distributaries.

[Illustration: FIG. 1.]

From each distributary “watercourses” take off at intervals and convey
the water to the fields. A small canal, say one whose length is not more
than 15 miles or whose discharge is not more than 100 c. feet per
second, may be regarded as a distributary and the word distributary will
be used with this extended meaning.

It is not always the case that the whole tract covered by a system of
canal channels is irrigated. In the case of a canal fed from a river,
the land near the river is often high or broken and the main canal runs
for some distance before it reaches the tract to be irrigated. Again,
within this tract there are usually portions of land too high to be
irrigated. Those portions of the tract which can be irrigated are called
the “commanded area.”

The channels of a large irrigation system should run on high ground. In
the case of a distributary, this is necessary in order that the
water-courses may run downhill, and since the water in the canal and
branches has to flow into the distributaries, the canal and branches
must also be in high ground. Another reason for adopting high ground is
that all the channels should, as far as possible, keep away from the
natural drainage lines of the country and not obstruct them. Also a
channel in high ground is cheapest and safest. When a channel is in low
ground it must have high banks which are expensive to make and liable to
breach. Every tract of country possesses more or less defined ridges and
valleys. When the ridges are well defined, the irrigation channels,
especially the distributaries, follow them approximately, deviating
slightly on one side or the other from the very top of the ridge in
order to secure a more direct course. If any part of a ridge is so high
as to necessitate deep digging the channel does not necessarily go
through it. It may skirt it and return to the crest of the ridge further
on, especially if this arrangement shortens the channel or at least does
not lengthen it much. A channel also goes off the ridge sometimes when
adherence to it would give a crooked line. Of course all the
channels--canals, branches and distributaries--have to flow more or less
in the direction of the general slope of the tract being dealt with.

[Illustration: FIG. 2.]

The alignments of the channels do not, however, depend exclusively on
the physical features of the country. Centrality in the alignment is
desirable. It will be shown (CHAP. II. Art. 10) that a distributary
works most economically when it runs down the centre of the tract which
it has to irrigate. It is better to have short watercourses running off
from both sides of a distributary than long watercourses from only one
side. The same is true of a branch; it should run down the centre of its
tract of country. Again the angles at which the channels branch off have
to be considered. If branches were taken off very high up the canal and
ran parallel to and not far from it, there would be an excessive length
of channel. But neither should the branches be so arranged as to form a
series of right angles. In the case shown in Fig. 2 the size of the
main or central canal would of course be reduced at the point A. By
altering the branches to the positions shown in dotted lines their
length is not appreciably increased while the length A B is made of the
reduced instead of the full size. Moreover the course B C is more direct
than BAC and this may be of the greatest importance as regards gaining
the necessary command. When a channel bifurcates, the total wet border
always increases and there is then a greater loss from absorption. The
water is always kept in bulk as long as possible. If the alignment of a
branch is somewhat crooked it does not follow that straightening
it--supposing the features of the country admit of this--will be
desirable. It may increase the length of distributaries taken off near
the bends. It will be shown (CHAP. II. Art. 10) that a distributary
ought, when matters can be so arranged, to irrigate the country for two
miles on either side of it, and watercourses should be two or three
miles long. A distributary need not therefore extend right up to the
boundary of the commanded area but stop two or three miles from it.
Generally it is not desirable to prolong a distributary and make it
“tail” into another channel (CHAP. II. Art. 3). A distributary, like a
canal, may give off branches.

None of the rules mentioned in the preceding paragraph are intended to
be other than general guides, to be followed as far as the physical
features of the country permit, or to assist in deciding between
alternative schemes. It may for instance be a question whether to
construct one distributary or two, between two nearly parallel branches.
The two-mile rule may enable the matter to be decided or it may
influence the decision arrived at as to the exact alignments of the
branches. The flatter the country and the less marked the ridges the
more the alignment can be based on the above rules. Sometimes, as in the
low land adjoining a river, the ridges are ill defined or non-existent
and the alignment is based entirely on the above rules. The rule as to
following high ground need not be adhered to at the tail of any
distributary if all the land to be irrigated at the tail is low and if
there is a deep drainage line or other feature of the country such as to
preclude the possibility of an extension of the distributary. Possible
extensions should always be considered. In hilly districts an irrigation
canal may have to run in sidelong ground along the side of a valley.

In flat valleys, owing to the land nearest the river having received
successive deposits of silt in floods, the ground generally slopes away
from the river and a canal can irrigate the low land even if taken off
at right angles to the river. But to irrigate the high land near the
river and the land where it rises again towards the hills or watershed,
a canal taking off higher up the river is necessary. Of course much
depends on whether the canal is to irrigate when the river is low or
only when it is high, and whether or not there is to be a weir in the
river. In Upper Egypt, it is common for a high level canal taking off
far upstream, to divide into two branches, one for the land near the
river and one for the land towards the watershed, and for both branches
to be crossed--by means of syphons--by a low-level canal which irrigates
the low ground. Similar arrangements sometimes occur on Indian
inundation canals.

Regulators are usually provided at all off-takes of branches. In the
case of a channel taking off from another channel many times its own
size there is generally only the head regulator of the smaller channel
but in other cases there is a regulator in each channel below the
bifurcation. Thus, when the number of bifurcating channels is two it is
called a double regulator. Regulators, with the “falls”--introduced to
flatten the gradients when the slope of the country is too steep--and
drainage crossings and the bridges, provided at the principal roads,
constitute the chief masonry works on a canal. At a fall, mills are
often constructed or the fall may be used for electric power.

Regarding curves and bends in channels, it is explained in _River and
Canal Engineering_ that, as regards increased resistance to flow and
consequent tendency to silt deposit, curves of fair radius have very
little effect, that a curve of a given angle may perhaps have the same
effect whether the radius is great or small but that if the radius is
large a succession of curves cannot be got into a short length, that a
succession of sharp curves in a short length may have great effect,
amounting to an increase of N in Kutter’s co-efficient, that a single
sharp curve has not much effect, that the chief objection to such a
curve is the tendency to erosion of the bank, that at a place where the
channel has, in any case, to be protected, as for instance just below a
weir or fall, there is no objection to the introduction of a sharp bend
and that such bends, in fact right-angled elbows, exist without any evil
effects at many regulators when the whole supply is being turned into a
branch. It is remarkable that on perennial canals no advantage is ever
taken of the last mentioned fact. Cases undoubtedly occur, though
somewhat infrequently, in which the most suitable and cheapest
arrangement would be to give a canal an abrupt bend at a fall. In order
to reduce eddying, the bend need not be an absolute elbow but can be
made within the length of the pitching which would be curved instead of
straight. This is frequently done on inundation canals, without the
slightest drawback, even when there is no fall, the pitching at bridges
being utilised. A pitched bend can be made anywhere.

When a river floods the country along its banks as in parts of Egypt and
of the Punjab, it is generally necessary to construct marginal
embankments before irrigation can be introduced. The canal may take off
at a point where flooding does not occur or it may pass through the
embankment.[2] If it passes through at a point where flooding occurs, a
masonry regulator is constructed to prevent the floods from enlarging
the gap and breaking into the country.

  [2] For detailed accounts of such embankments and canals see _Punjab
  Rivers and Works_ (Spon) 1912.

A large canal is provided, so far as is practicable, with “escapes” by
means of which surplus water may be let out. Surplus water occurs
chiefly after rain. At such times the demand for water may suddenly be
reduced and if there were no escapes there would probably be serious
breaches of the banks before there was time for the reduction of water,
effected at the head of the canal, to take effect lower down. There is
usually an escape at some point in the main line, preferably at a point
where it divides into branches, and this escape runs back to the river.
There may also be escapes near the tails of the longest branches. These
escapes may discharge into drainages or into reservoirs formed by
running a low embankment round a large area of waste land.

The drainage of the whole tract irrigated by a canal must be carefully
seen to. The subsoil water level of a tract of country is nearly always
raised by an irrigation canal. The rise near to a canal or distributary
is due to percolation from the channel and is inevitable.[3] The rise at
places further away, if it occurs, is due to over-watering or to neglect
of drainage. Immense damage has been done by “water-logging” of the soil
when irrigation water has been supplied to a tract of flat country and
the clearance and improvement of the natural drainages has not been
attended to. Any drainages crossed by the banks of the irrigation
channels should be provided with syphons or aqueducts or else the
drainage diverted into another channel. Very frequently the main line of
a canal--whether great or small--in the upper reaches near the hills,
has to cross heavy drainage channels or torrents and large and expensive
works are required for this.

  [3] But see Chap. V. as to reduction of percolation.

Near the head of a canal and of every branch and distributary, there is
an ordinary gauge which shows the depth of water and is read daily. The
gauge near the head of a main canal is generally self-registering.

The principles sketched out in this article are those generally followed
in the designs of modern canals. They have by no means been followed in
all cases. In some of the older Indian canals both the canal and the
distributaries ran in low ground. Water-courses took off direct from the
canals, and the irrigation did not generally extend far from the canal.
In fact long distributaries were impracticable because they would have
run into high ground. The banks of the channels obstructed drainages and
caused pestilential swamps. Most canals of this type have been
abolished since the advent of British rule and replaced by others
properly designed. Some badly designed canals however, mostly of the
inundation class, still exist but in very dry tracts where drainages are
of little consequence.


3. =Information Concerning Canals.=--Nearly all canal irrigation is done
by “flow,” the water running from the water-courses onto the fields, but
a small proportion is done by “lift.” This is done in the case of high
pieces of land, the lifting being usually done by pumps or, in the east,
by bullocks or by manual labour.

Irrigation generally consists in giving the land a succession of
waterings, one previous to ploughing and others after the crop is sown,
each watering being of quite moderate depth. On inundation canals in
India the waterings for the summer crop are thus effected but for the
winter crop the land is deeply soaked during the flood season and is
afterwards ploughed and sown. In Upper Egypt this system is emphasised,
the water flowing into vast basins, formed by dykes, where it stands for
some time and, after depositing its silt, is drained off.

Until recent times the whole of the irrigation of Egypt was basin
irrigation. In Lower Egypt the construction of the Nile barrage led to
the introduction of canals which take off at a proper level and their
working is not restricted to the period when the river is in flood. In
Upper Egypt most of the irrigation is still basin irrigation but the
canals taking off above the Assiut barrage form a notable exception. By
means of the Assouan dam which crosses the Nile, the water during the
latter part of the flood season and after the floods are over, i.e. from
November to March, is ponded up and a vast reservoir formed and the
impounded water is let down the river in May and June.

In some of the older irrigation canals of India the velocity was too
high and the channels have since had to be remodelled and the crests of
weirs raised or new weirs built. The more recent canals are free from
grave defects of this kind but every canal undergoes changes of some
kind and finality has never yet been quite attained.

On some Indian irrigation canals made about 30 years ago, great sums of
money were wasted in making the canals navigable. There is nothing like
enough navigation to pay for the extra cost. The idea has now been quite
given up except as regards timber rafting from upstream. This requires
no curtailment of the velocity in the channels. The requirements of the
irrigation and navigation were always in conflict. The mere fact that
branches have to be worked in turns is enough to prevent navigation
succeeding.

In India the water used for irrigation is paid for, not according to the
volume used but according to the area irrigated. The volume used in any
particular watercourse is not known. The areas sown are measured.
Certain kinds of crops use up more water than others and the charges are
fixed accordingly.

In the canals which have their headworks among the mountains of Western
America there are frequent tunnels and syphons and the canals often run
in steep sidelong ground. There are great lengths of tunnel and syphon
in the Marseilles and Verdun Canals and there are long tunnels in the
Periyar Canal in Madras and in the Upper Swat Canal in the North West
Frontier Province of India.

The Tieton Canal, Washington, U.S.A., traverses steep sidelong ground
which would be liable to slip if a large cutting were made. The
cross-section of the channel is a circle, 8-ft. 3¹⁄₂-ins. in diameter,
with the upper part removed, so that the depth is 6 feet. It is made of
reinforced concrete 4 inches thick and the sides are tied together by
iron bars which run across the channel above the water. In the Santa Ana
Canal the channel consists for 2¹⁄₂ miles of a flume made of wooden
“staves.”

A canal constructed in Wyoming, U.S.A., after taking off from a river,
passes through a tunnel into another valley and is turned into another
stream which thus becomes the canal. This is said to save loss of water
by percolation. The stream is winding while a canal could have been made
straighter. There may, owing to the ground near the stream being
saturated, have been less loss of water at first than there would have
been in the artificial channel but, owing to the smaller wetted area,
there would probably have been an eventual saving in adopting the
latter. The real advantage of adopting the natural stream was probably a
saving in the cost of construction. (_Min. Proc. Inst. C.E._ Vol.
CLXII.)

Irrigation from canals which are supplied from reservoirs differs in no
respect from that from other canals. The principles on which reservoir
capacities should be calculated and earthen and masonry dams constructed
are given in _River and Canal Engineering_. Sometimes, as for instance
when a reservoir becomes seriously reduced in size owing to silt
deposit, the water is run off after the bed of the reservoir has been
soaked, and crops are grown on the soaked soil.

The distribution of the water of a canal as between the main channel and
the branches, is effected by means of the regulators at the
bifurcations. When the supply is ample and the demand great, the
channels may all be running nearly full. When the demand exceeds the
supply, the water may be reduced proportionately in each branch but this
may result in the water of a branch being too low to give proper
supplies to the distributaries or some of them, and in the water of a
distributary not commanding the higher ground. Moreover it violates the
principle of keeping the water in bulk as far as possible. It is more
usual to give each branch full supply, or a certain large fraction of
the full supply, in turn, and similarly with the distributaries.

The method of distribution from a distributary to the watercourses
varies. In many modern canals there is, at each watercourse head, a
sluice which is adjusted at frequent intervals according to the supply
and the demand. One method, which is excellent because it fulfils in the
highest degree the principle of keeping the water in bulk, is to have
very large watercourses and, by means of regulators which are built at
frequent intervals, to turn the whole of the water of the distributary
into a few watercourses at a time, beginning with those nearest the head
of the distributary and working downstream. But a system which seems
eminently suitable may be impracticable because of local circumstances.
In India, any such arrangement would need an army of officials and would
lead to unbounded corruption.

In India the water from a distributary enters the watercourses through
“outlets” which are small masonry tubes passing through the banks of the
distributary. There is no easy way of closing these outlets or at least
of keeping them closed if the cultivators choose to open them, but it is
easy to close a whole distributary and so regulate the supply. This is
the chief reason why watercourses in India do not usually take off
direct from the canals.

The presence of silt in the water of a river from which a canal is drawn
is often spoken of as being a great evil. If it is an evil at all it is
a very mixed evil. The deposits of silt in the channels have been
enormously reduced by the application of scientific principles of
design. The clayey silt which remains in the water and reaches the
fields, brings to them greatly increased fertility.

In India the fertility of the soil is often reduced or destroyed by the
formation on the surface of the ground of an efflorescence called “reh.”
It consists of various salts or compounds of sodium and occurs chiefly
where there is an impervious layer of subsoil. The salts exist as an
ingredient of the upper soil. This becomes saturated with rain or canal
water and as the water evaporates the salts are left on the surface.
Remedies are drainage, or flooding the soil and running the water off,
or deep tilling, or chemical treatment with lime or gypsum. (_Indian
Engineering, 8th Jan., 1910_).

The inundation canals of the Punjab have been described in _Punjab
Rivers and Works_. All descriptions and remarks in the present book
regarding Indian canals must be assumed to refer to perennial canals
unless the contrary is stated or implied.


4. =Losses of Water.=--When water flows or stands in an earthen channel
or tank, or is spread over a field, losses occur from evaporation,
percolation and absorption. Of these, absorption is by far the most
important and, unless the contrary is stated or implied, it will be
taken to include the others. The losses by evaporation are very small.
The loss by evaporation from the surface of the water, even in the hot
season in India when a hot wind often blows, does not exceed half an
inch in 24 hours and on the average in India is only about a tenth of an
inch in 24 hours.

[Illustration: FIG. 3.]

Percolation and absorption are described as follows by Beresford in
_Punjab Irrigation Paper_, No. 10, “The Irrigation Duty of Water.”
Percolation consists in flow through the interstices of boulders,
shingle, gravel or coarse sand. The flow is similar to that in pipes.
The water percolating into the soil from a channel, extends downwards
and spreads outwards as it descends. None of it goes upwards. In fine
sand and ordinary soil the interstices act like capillary tubes. The
water is absorbed as by a sponge and it remains in the soil by virtue of
capillarity. Owing to the combined action of capillarity and gravity the
water spreads in the manner shown by the dotted lines in Fig. 3. The
amount of absorption from a channel will be greater the greater the area
of the wetted surface. In a high embankment with narrow banks, the
absorption ceases when the water reaches the outer slopes, except in so
far as it is evaporated from the slopes. Moreover high embankments are
generally in clayey soil. If banks of sand are constructed on a layer of
clay (Fig. 4.) and well rammed, the absorption ceases as soon as the
banks are saturated and the channel then holds water as well as any
other except for evaporation from the outer slopes, but if the bed and
subsoil are also of sand the absorption of the water will be far
greater. Absorption ceases when the water extends nearly down to the
level of the subsoil water, i.e., to a point where the effect of
absorption from above plus gravitation is equal to the effect of
absorption from below minus gravitation. If a bottle is filled with
water and a small sponge jammed into the neck and the bottle turned
upside down, the sponge becomes saturated but no water will be given
out. But if a dry sponge is placed in contact with the wet one it will
absorb moisture until saturated.

[Illustration: FIG. 4.]

It is known that the loss of water is greatly influenced by the nature
of the soil. When water is turned into a dry channel or onto a field,
the loss is at first great. It decreases hourly and daily and eventually
becomes nearly constant, tending to reach a fixed amount when the water
extends down to nearly the level of the subsoil water. Observations made
by Kennedy on loamy fields near the Bari Doab Canal in India showed that
on a field previously dry the rate of absorption is given by the
equation

  _y_ = ·0891_x_^{·86.}

Where _y_ is the depth of water absorbed in feet and _x_ is the time in
hours. The observations extended over eight days. Denoting by _c_ the
depth of water in feet absorbed in one hour, it was found that on a
field on which no rain had fallen for two months, _c_ was ·04 to ·05 but
on the second watering of the crop about a month later _c_ was ·02 to
·03 and about the same on a third watering. It was found that at the
first commencement the rate of absorption was much affected by the state
of the surface of the ground but that the effect was only temporary. The
losses were found to be as follows:

  +------+--------------+---------------+
  | DAY. |LOSS PER DAY. | LOSS PER HOUR.|
  |      |              |     (_c_)     |
  +------+--------------+---------------+
  |      |       Feet.  |     Feet.     |
  | 1st  |       1·36   |     ·057      |
  | 2nd  |       1·13   |     ·047      |
  | 3rd  |       1·07   |     ·046      |
  | 4th  |       1·02   |     ·043      |
  | 5th  |        ·96   |     ·041      |
  | 6th  |        ·90   |     ·037      |
  | 7th  |        ·80   |     ·033      |
  | 8th  |        ·77   |     ·032      |
  |      | Total 8·01   |               |
  +------+--------------+---------------+

In the eight days the total loss was almost exactly eight feet.

The losses by absorption in the various channels of certain canals has
been estimated to be as follows:--

  ---------------+-------+----------+-------+-----------+---------------
     Channel.    | Nature|Mean depth| Value |  Loss per |   Remarks.
                 |  of   | of water |   of  |  Million  |
                 | soil. |    in    | (_c_) |square feet|
                 |       |  Channel.|       | of wetted |
                 |       |          |       |  surface. |
  ---------------+-------+----------+-------+-----------+---------------
                 |       |   Feet.  |       |   c. ft.  |
                 |       |          |       |  per sec. |
  Main Line Upper|Shingle|     6    |·035   |    9·7   }|
  Bari Doab Canal|and    |          |       |          }|
                 |Sandy  |          |       |          }|
                 |Soil   |          |       |          }|
                 |       |          |       |          }|Fairly reliable
  Main Line      |Sandy  |     7    |       |    9·0   }|estimates based
  Sirhind Canal  |Soil   |          |       |          }|on discharge
                 |       |          |       |          }|observations.
  Branches Upper |Loam   |          |·0079  |    2·2   }|
  Bari Doab Canal|       |          |       |          }|
                 |       |          |       |          }|
  Branches       |Sandy  |          |       |    5·2   }|
  Sirhind Canal  |Soil   |          |       |          }|
                 |       |          |       |           |
  Distributaries |Loam   |          |·012[4]|2·3 to 4·4}|
  Upper Bari     |       |          |       | (average }|
  Doab Canal     |       |          |       |   3·3)   }|
                 |       |          |       |          }|
  Distributaries |Sandy  |          |       |  5 to 12 }|
  Sirhind Canal  |Soil   |          |       | (average }|
                 |       |          |       |   8·0)   }|Somewhat rough
                 |       |          |       |          }|estimates.
  Watercourses   |Loam   |          |·015[4]| 3·3 to 20}|
  Upper Bari     |       |          |   to  | (average }|
  Doab Canal     |       |          |·045[5]|   9·4)   }|
                 |       |          |       |          }|
  Watercourses   |Sandy  |          |       | 7 to 60  }|
  Sirhind Canal  |Soil   |          |       | (average }|
                 |       |          |       |   22)    }|
  ---------------+-------+----------+-------+----------+----------------

  [4] When the channel was in continuous flow.

  [5] Maximum value when flow was intermittent.


Some information as to losses of water is also given in CHAPTER IV. Art.
2.

The relative losses of water in the channels of the Upper Bari Doab
Canal were as follows:--

                             Relative Loss.
  In main line and branches        20
  In distributaries                 6
  In watercourses                  21
  Used in the fields               53
                                  ---
                            Total 100

The reasons for the great variation in the value of _c_ are not properly
known. The depth of water is not likely to have much influence on it. It
is well known that the fine silt carried by the water tends to render
the channels watertight when it deposits. The canals and branches
receive either no deposits or deposits consisting chiefly of sand. The
distributaries, especially in their lower reaches, receive deposits of
fine silt which is only occasionally cleared away. The watercourses
receive similar deposits but they are very frequently cleared out by the
cultivators. This is perhaps the reason why the rate of loss of water in
the watercourses is nearly three times as great as the rate of loss in
the distributaries of the same canal. On the Sirhind canal the
distributaries have more branches than on the Bari Doab canal and the
watercourses are smaller. This accounts for the different relative
losses in the two cases. The sandy nature of the soil on the Sirhind
canal accounts for the general higher value of _c_ on that canal.

The following formula has been deduced as giving the loss by absorption
on a Punjab Canal.

                 WL
  P = 3·5 √d ---------
             1,000,000

Where P is the loss by absorption in c. ft. per second in a reach whose
length is L, width (at water level) W and depth d. According to the
formula the loss per million square feet is 10·5 c. ft. per second when
d is 4 ft. and 7 c. ft. per second when d is 2 feet, These figures do
not agree with those in the preceding table and it is clear that there
are not yet sufficient data from which to construct a formula.

The first steps taken on the Bari Doab Canal, and subsequently on other
canals, to reduce the losses of water, consisted in the reduction in the
number of watercourses. This will be referred to again (CHAPTER II. Art.
9). Further steps will be considered in CHAPTER V.


5. =Duty of Water.=--The number of acres irrigated annually by a
constant discharge of 1 c. ft. of water per second is called the “duty”
of water. In India on perennial canals the duty may be as much as 250 or
even 300 acres. On inundation canals which flow for only five months in
the year and are situated in tracts of scanty rainfall and light or
sandy soil, the duty may be only 70 acres. The duties of most existing
canals whether in India or elsewhere, are known only approximately. The
duty is calculated on the average discharge entering the canal at its
head less the water which is passed out at escapes. It thus includes all
losses of water. The duty varies not only as between one canal and
another but on the same canal from year to year. It depends on the
character of the soil, a sandy soil requiring more water than a clayey
soil. It also depends on the rainfall. A moderate amount of rain causes
the canal water to go further, but heavy rain may enable some crops to
do without canal water or may permit of the concealment of canal
irrigation. The duty also depends on the kind of crops grown, on the
losses in the channels by absorption and on the quantity of water
available. A liberal supply of water leads to carelessness in the use,
but a very restricted supply is largely wasted owing to the shortness of
the “turns” or rotational periods of flow in the different channels.

There is an obvious connection between the duty of water and the total
depth of the water, known in India as “delta,” given to the fields.
Calculations are much simplified, while still being accurate enough for
all practical purposes, by assuming that the number of seconds, (86,400)
in a day is twice the number of square feet, (43,560) in an acre.
Assuming this to be the case a discharge of 1 c. ft. per second for a
day gives 2 acre-feet, i.e., it will cover an acre of ground to a depth
of 2 feet in a day; and in six months it will cover 100 acres to depth
of 3·65 feet. In Northern India the year is divided into two halves in
each of which a crop is grown and the duty is calculated for each crop.
In this case, if the flow of a canal has been continuous, a duty of 100
acres per cubic foot of its mean discharge per second, corresponds to a
total depth of 3·65 feet over the area irrigated. Generally the flow in
the half-year has not been continuous. In other countries, and in India
on canals other than the perennial canals, the periods of flow vary a
great deal. The duty cannot be calculated from delta or _vice versa_
until the period of flow is stated.

The daily gauge-readings and daily discharges corresponding to them,
having been booked, the discharges are added up. The total, divided by
the number of days on which the canal has been running, gives the
average daily discharge. Suppose that during the “kharif” or summer crop
which is considered to last from 1st April to 30th September or 183
days, the canal was closed for 13 days and that the total of the daily
discharges on the remaining 170 days comes to 850,000 c. ft. per second.
The average daily discharge is 5,000 c. ft. per second. Suppose the
kharif area irrigated to be 500,000 acres, the kharif duty is 100 acres.
To find delta the total of the daily discharges has to be multiplied by
the number of seconds in a day and divided by the number of square feet
in an acre (these figures are, as already stated, very nearly in the
ratio of two to one) and divided again by the number of acres irrigated.
Thus, in the above case, delta is very nearly 850,000 × 2/500,000 or 3·4
feet. For comparing the results of one canal or one year with another,
delta is the more convenient figure to take. As soon as the areas
irrigated by the canals are known for any crop, the Chief Engineer of
the province issues a statement of the value of delta for each perennial
canal and compares them with those for previous years. The value of
delta for the Punjab canals ranges from 3 to 4 feet for the kharif and
from 1·8 to 2·1 feet for the “rabi” or winter crop. Individual canals
vary greatly, the worst having nearly twice as high a figure as the
best. The differences are due to the causes already mentioned.

Although the figures of duty take no account of the number of days a
canal was closed, they are the most convenient standard for judging
generally of the work likely to be done by a projected canal. It will
readily be seen that figures of duty are not exact and are only an
approximate guide. The delta figures are, on the perennial canals of the
Punjab, also worked out for each month of the crop, the volume of water
used from the beginning of the crop up to the end of the month being
divided by the area irrigated up to the end of the month. But when
irrigation is in full swing, some little delay occurs in booking the
fields. Moreover the same field is watered a number of times during the
crop and much depends on whether waterings have just been given or are
just about to be given. The figures are useful to some extent for
comparison. The figures for the rabi crop of 1908-09 were as follows,
the figure for March being the final figure for the crop.

  Up to end of                 Oct.,  Nov.,  Dec.,  Jan.,  Feb.,  March.
  Progressive value of delta.  1·69   1·34   1·29   1·47   1·71   2·05.

One great principle to be followed in order to obtain a high duty is to
restrict the supply of water. A cultivator whose watercourse is always
running full may waste great quantities of water, but if he knows that
it is only to run for a few days out of a fortnight he will use the
water carefully. It is not, of course, meant that the water kept back is
run into escapes and wasted. It goes to irrigate other lands. The
available supply of water should be spread over as large an area of land
as just, and only just, to suffice.[6] Other methods of improving the
duty are the reduction in the number of watercourses, the apportionment
of the sizes of outlets, watercourses and distributaries to the work
that they have to do, careful attention to the distribution of the water
and the prevention of wastage due to carelessness.

  [6] A system of lavish supply is in most cases likely to lead to harm
  by water-logging of the soil or its exhaustion by over-cropping or to
  raising of the spring level and injury to the public health.

The following information concerning duties is taken from Buckley’s
Irrigation Pocket Book:--

  +---------------------+-------------+-----------+
  |      PLACE.         | RABI DUTY.  |KHARIF DUTY|
  +---------------------+-------------+-----------+
  |                     |   Acres     |  Acres    |
  |                     |             |           |
  |Upper India          |135 to 237[7]| 49 to 120 |
  |(Punjab and          |             |           |
  |United Provinces)    |             |           |
  |                     |             |           |
  |Lower Chenab Canal[8]|133 to 134   | 47 to  88 |
  |(Punjab)             |             |           |
  |                     |             |           |
  |Bengal               | 56 to 130   | 57 to 113 |
  |                     |             |           |
  |Bombay               | 85 to 118   | 58 to 159 |
  +---------------------+-------------+-----------+

  [7] Occasionally as low as 98 or even 62.

  [8] The most recent canal.

The period of flow in each case would be six months or less.

The average rabi duties on the Lower Chenab and Upper Bari Doab Canals,
in the Punjab, calculated on the discharges at the distributary heads,
for periods of 3 and 5 years respectively, ending March, 1904, were 208
and 263 acres respectively, but in the latter case 11 per cent. of the
area received only “first waterings.” For the kharif the figures are 100
and 98 respectively.

In Italy the duty is 55 to 70 acres, in Spain from 45 to 205 acres, in
the Western States of America generally 60 to 150 acres. In South
California the duty is 150 to 300 acres, when, as is usual, surface
irrigation is employed, but 300 to 500 acres with subsoil irrigation,
the water being delivered in a pipe below ground level (CHAPTER V.)

In basin irrigation in Egypt the duty is 20 to 25 acres, but the period
of flow is only 40 days. The basins are flooded to about 3 feet in
depth.


6. =Sketch of a Project.=--The tract of country to be dealt with in an
irrigation project may be limited either by the natural features of the
country, by its levels, by the quantity of water available or by
financial considerations. If the tract is small or narrow, and
particularly if it is not very flat, it may be obvious that there is
only one line on which the irrigation channel can conveniently be
constructed but in any considerable scheme a contour plan of the whole
tract is absolutely necessary. The surveys for such a plan are expensive
and take time and it is desirable, as far as possible, to settle
beforehand the area over which they are to extend. This may be done to
some extent by the examination of any existing levels and of the tract
itself. Very high, sandy or swampy ground, whether occurring at the edge
of the tract or in the middle of it, may have to be left out. The
remainder, as already mentioned, is called the commanded area. When land
occupied by houses or roads or which is very much broken, or which for
any reason cannot be irrigated, has also been deducted, the balance is
the “culturable commanded area.”

Either before or after the culturable commanded area has been
approximately ascertained, the proportion of it which is to be irrigated
must be settled. This depends on local circumstances. In India the
supply of water is calculated on the supposition that a fraction,
generally from ¹⁄₃ to ³⁄₄, of the culturable commanded area will be
irrigated each year. The rest will be lying fallow or be temporarily out
of use or be used for crops which do not require canal irrigation. The
restriction of the area is necessary either because the supply of water
is limited or in the interests of the people. Too liberal a supply of
water tends, as already stated, to over cultivation, and exhaustion and
water-logging of the soil.

The next step is to estimate the duty and the discharge of the canal and
then to fix its main dimensions. In Northern India the duty in the rabi
is higher than in the kharif. It may be 200 acres in the rabi and 100
acres in the kharif. Local circumstances determine which crop has the
greater area. Suppose that it is estimated that both will be equal. Then
the total annual area for which water is to be provided must be divided
by two and this gives the kharif area. During the kharif there is
usually an ample supply of water and the kharif mean supply of the canal
is based on the kharif area and the kharif duty. The full supply is not
run all through the crop because the demand fluctuates, the demand being
greatest when all the crops have been sown and when there is no rain,
but from experience of other canals the ratio of the kharif full supply
to the kharif mean supply can be estimated. The ratio is generally about
1·25. On the kharif full supply depends the size of the channel, every
channel being constructed so as to carry a certain “full supply” or
maximum discharge and the top of the bank being made at such a height
that there shall be a sufficient margin or “free-board” above the “full
supply level.” The canal runs full provided that there is a sufficient
supply in the river or that the water level of the river is high
enough--this last condition referring to canals which have no weir in
the river--and provided also that there is a sufficient “demand” for the
water. At other times a canal runs with less than full supply. This
generally occurs throughout most of the rabi, the supply of water in the
river being then restricted. The distributaries are generally run full
or ³⁄₄ths full, some being closed, in turn, to give water to the others.
In the case of a country where there is only one crop in the year, the
average discharge of the canal can be found by dividing the area by the
estimated duty. The F.S. discharge can be assumed to bear such a
relation to the average discharge as may be found by experience to be
suitable. On some Indian inundation canals the F.S. discharge is taken
as twice the average discharge.

The F.S. discharge of the canal having been arrived at, the alignments
of the canal and branches are next sketched out on the contour plan and
certain tracts and discharges are assigned to each branch. The gradients
can be ascertained from the levels of the country and the cross-section
of the channel can then be sketched out. If the velocity is too great
for the soil “falls” can be introduced. The above procedure will enable
a rough idea to be formed of the cost of the earthwork of the scheme.
The cost of the headworks and masonry works and distributaries can be
best estimated by obtaining actual figures for existing works of similar
character, the distributaries being reckoned at so much per mile. The
probable revenue which the canal will bring in will depend upon the rate
charged for the water and the cost and maintenance, matters which can
only be determined by local considerations based on the figures for
existing canals.

The masonry works on a canal consist of the headworks and of bridges,
regulators and drainage crossings. The principles of design for such
works have been dealt with in _River and Canal Engineering_. It is of
course economical to make a bridge and fall in one. If the off-take of a
distributary is anywhere in the neighbourhood the fall should of course
be downstream of it. The positions of the falls should be fixed in
accordance with these considerations. If the longitudinal section is
such that the position of the fall cannot be much altered, it may be
feasible to divert a road so that the bridge may be at the best site for
the fall. In the case of a railway crossing, a skew bridge is often
necessary. In the case of a road crossing it may be feasible to
introduce curves in the road but here also a skew bridge is often
necessary.




CHAPTER II.

THE DESIGNING OF A CANAL.


1. =Headworks.=--In the design of head works no very precise rules can
be laid down. Some general ideas can however be given as to the chief
points to be attended to and some general and approximate rules stated.
In every case a large scale plan of the river is of course required and
also a close examination of it and study of its character. An attempt to
forecast its action is then possible. Gauge readings for several years
and calculations of discharges are of course necessary. If the bed of
the river, in course of time, rises upstream of the weir or scours
downstream of it, a large amount of protection to the bed and banks will
become necessary. Some description of headworks and weirs, with a plan
of the headworks of the Sirhind Canal, India, has been given in _River
and Canal Engineering_, CHAPTERS IV. and X. Remarks regarding the
collection of information for such works are given in CHAPTER II. of the
same work. It is also explained how, by keeping the gates of the
under-sluices closed, a “pond” is formed between the divide wall and the
canal head so that heavy sand deposits in the pond and does not enter
the canal. By closing the canal and opening the under-sluices the
deposit is scoured away.

The best site for the headworks of a canal depends on the stability and
general character of the bed of the river but in deciding between any
two proposed sites, the question of the additional cost of the canal, if
the upper site is adopted, has to be taken into account. Such cost may,
in rugged country, be considerable.

In the case of Indian perennial canals, the head is often close to the
hills where the river bed is of boulders and shingle and fairly stable,
but it is often at a distance from the hills and in such cases a gradual
rise in the bed of the river, even in the absence of a weir, is more
probable than scour. Such a rise may necessitate a raising of the crest
of the weir and of the bed of the canal.

[Illustration: FIG. 5.]

In the general arrangement of a headworks a great deal depends on local
conditions. Sometimes the river runs in a fairly straight and defined
channel and the weir can then be run straight across it. Sometimes, as
in the case of the Ganges Canal, there is a succession of islands and
various short weirs are required in the different channels. At the heads
of the Eastern and Western Jumna Canals, the river, on issuing from the
hills, widens out (Fig. 5.) and the weir is built obliquely and not in
a straight line. Its crest is higher at the east than at the west side.
There are under-sluices at both sides. The upstream end and west side of
the island are revetted. The old head of the Western Jumna Canal, as
shown in the figure, existed long before the advent of the British, and
a temporary weir, made of gabions filled with stones, was constructed
across the river every year during the low water period and swept away
during the floods. To have carried the weir along the line shown dotted,
the head of the Western Jumna Canal being of course brought up to it,
would apparently have been feasible and cheaper, but the off-take would
have been in shallow water because of the curve in the river, and there
would have been no current along the face of the head regulator of the
canal.

The level of the floor of the under-sluices is generally about the same
as that of the bed of the canal. The sill--made to exclude shingle and
sand as far as possible--of the canal head regulator may be 3 feet
higher and the crest of the weir 6 to 9 feet higher. The top of the weir
shutters is 1 to 2·5 feet above the F.S. level of the canal which may be
5 feet or more above the bed of the canal. If the weir is provided with
falling shutters the width of the waterway of the under-sluices may be
about ¹⁄₁₂th of the width of the waterway of the weir alone, otherwise
about ¹⁄₈th.

In nearly all cases the weir has a flat top and flat slopes both
upstream and downstream. In a case where the river bed is of sand, the
depth of water on the crest of the weir in floods may be 15 feet and the
velocity 14 or 15 feet per second. The downstream slope of the weir may
be about 1 in 15, and the upstream slope 1 in 6. Where the river bed is
of boulders the velocity may be still higher. The faces of the weir are
usually of hammer-dressed stone. A lock for the passage of rafts is
added if necessary.

Unless the banks of the river are high, it is necessary to construct
embankments to prevent the river water, when headed up by the weir
during the floods, from spilling over the country with possible damage
to the canal. If the river has side channels they have to be closed. The
stream may also have to be trained, by means of guide banks or spurs, so
as to remain in one channel and flow past the canal head and not form
shoals against it. Where the river is unstable, it may shift its course
so as to strike the weir obliquely and this may cause excessive heading
up at one side of the weir. In such cases it is usual to divide the weir
into bays or sections, each about 500 feet long, by “divide walls”
running at right angles to the weir.

The free-board or height of the masonry walls and tops of embankments
above H.F. Level is about 5 feet.

The span of each opening in the under-sluices is generally 20 to 35
feet. The piers may be 5 feet thick. It is usual to make each alternate
pier project upstream further than the others so that long logs coming
down the river during floods, broadside on, may be swung round and not
be caught and held against the piers.

[Illustration: FIG. 6.]

[Illustration: FIG. 6A.]

Figs. 6 and 6A show the headworks of the Upper Chenab Canal now under
construction (CHAPTER IV.) The site is in a low flat plain, but no
better site could be found. The weir consists of 8 bays of 500 feet
each. The crest is 10 feet above the river bed and the falling shutters
6 feet high. The slopes are 1 in 6 and 1 in 15. The bulk of the work is
rubble masonry in lime. The lower layer upstream of the crest is of
puddle; upstream of the second line of wells it is rubble masonry in
half sand and half lime; upstream of the lower line of wells it is of
dry stone and there is an intermediate layer of rubble masonry in lime
with the stones laid flat. Below the crest there is a wall of masonry 9
feet thick and on the crest there are two strips of ashlar between which
the shutters lie when down. The extreme upstream and downstream portions
of the bed protection are of dry stone and 4 feet thick while next to
the weir are concrete blocks 2 feet thick resting on dry stone. The
width of the crest is 14 feet, of the weir 140 feet, of the protection
70 feet upstream and 110 feet downstream. The guide banks have tops 40
feet wide and 18 and 14 feet above the crest of the weir in the upstream
and downstream lengths respectively, the side slopes being 2 to 1 and
the water slope being covered, up to H.W. level, by dry stone pitching 4
feet thick. The left guide bank runs upstream for 3,250 feet from the
centre line of the canal and the right 2000 feet from the line of crest
shutters. The under-sluices have 8 bays of 35 feet each and the canal
head regulator 36 openings of 6·5 feet each, the large openings shown in
the figure being sub-divided. The crest of the weir is no less than 10
feet above the river bed and the shutters add 6 feet to this. The floor
of the under-sluices is 4 feet higher than the river bed. There is thus
ample allowance for a possible rise in the river bed.


2. =The Contour Map.=--The contour map, besides showing the contours of
the country to be irrigated and of a strip of country, even if not to be
irrigated, which will be traversed by the main line, should show all its
main features, namely:--streams, drainages, railways, roads,
embankments, reservoirs, towns, villages, habitations, and the
boundaries of woods and cultivated lands. It should also show the
highest water levels in all streams or existing canals. A map showing as
many as possible of the above features should be obtained and lines of
levels run for the contours. In doing this, the points where the lines
of levels cut or pass near to any of the above features or boundary
lines, should be noted. It may be necessary to correct inaccuracies in
the plan or to supply defects in it. The greater the trouble taken to do
this the less will be the trouble experienced later on.

The heights of the contour lines will, in very flat country, have
eventually to be only 1 foot apart. This will necessitate running lines
of levels half-a-mile apart at the most, and preferably 2000 feet apart,
the pegs in each line being about 500 feet apart. In less flat country
the heights of the contour lines can be further apart than 1 foot.
Whatever distance apart is decided on for them, the survey should be
done once for all. On one of the Indian canals in flat country, the
lines of levels were at first taken 5 miles apart, the branches roughly
aligned and then further surveys made. This led to great expense and
delay and the procedure has not been repeated.

In making a contour survey, a base line, as centrally situated and as
long as possible, should be laid down, with side lines parallel to it
near the boundaries of the tract. The cross lines at half-mile or other
intervals should then be laid down. Some of them may run out beyond the
side lines. Circuits of levels should be run along the base line, the
side lines and the two extreme cross lines and be carefully checked. The
remaining cross lines should then be levelled. All the levels having
been shown on the map the contours should be sketched in. The scale of
the map for a large project may be two inches to a mile. If it is likely
that the survey will have to be extended, it will be easier to do this
by prolonging the base line and running more cross lines, than by
prolonging each of the cross lines already surveyed. This can be borne
in mind when selecting the base line.


3. =Alignments and Discharges.=--On the contour map the proposed
alignments of the canal, branches, distributaries, and escapes,
determined after careful consideration of all matters affecting them,
are shown. The tracts to be irrigated by each branch and each
distributary are now marked off, the “irrigation boundaries” following
approximately the valleys and lines of drainage. Any large tracts of
land which cannot be irrigated are of course shown and are excluded.
Forests or other lands which are not to be irrigated should be similarly
dealt with, otherwise confusion is likely to arise later. The commanded
area dependent on each distributary is now ascertained from the map. A
certain percentage being deducted for scattered unculturable areas the
culturable commanded areas are obtained. The proportion to be irrigated
(in India in the kharif) having previously been decided, the number of
acres to be actually irrigated by each distributary is arrived at.

The next step is to ascertain the discharges.[9] A general duty for the
whole canal having been estimated by considering the actual figures for
other canals the full supply of the canal at its head is arrived at.
(CHAPTER I, Art. 6). In Northern India it will be the kharif duty and
kharif full supply. Since some water is lost by absorption in the
channels, the duty of the water on a branch is higher than that of the
whole canal based on its head discharge, and the duty on a distributary
is higher still. In designing a canal, an attempt has to be made to
estimate the losses of water in the main canal and branches, so that the
duties of the branches and distributaries may be estimated and the
channels designed accordingly. On the Western Jumna Canal the figures
were estimated to be as follows:--

                                                           Kharif. Rabi.
  Average discharge at canal head (c. ft. per sec.)         3536   2755
  Duty based on the discharge (acres)                         98    138
  Estimated loss of water in canal and branches (c. ft. per
  sec.)                                                      400    300
  Average discharge at distributary head (c. ft. per sec.)  3136   2455
  Duty based on the discharge (acres)                        111    154

  [9] In this Article and in the rest of this Chapter it is assumed that
  the canal is a Northern Indian one. Any modifications necessary to
  suit canals in other countries will readily suggest themselves.

The question of duty is one which if not carefully considered, may cause
some confusion. A canal and branches, having been designed with certain
assumed duties and with discharges based on certain values of N in
Kutter’s co-efficient, have, let it be supposed, been constructed to a
greater or less extent. When the time comes for constructing the
distributaries, the engineers concerned may have different ideas, based
on later experience, as regards the probable duty and the most suitable
value of N. If they design the distributaries with a higher duty and a
lower value of N, it is obvious that they can provide more
distributaries than at first designed, or can increase their lengths. In
either case they would provide for an increased commanded area. If they
do not do this, they ought to adhere to the values at first proposed,
thus making the channels larger than, according to their ideas, would be
necessary. These larger channels will be able to do more irrigation, by
an increase, not in the commanded area, but in the proportion of it
which is irrigated. Any other course would result in the canal carrying
more water than could presumably be used by the distributaries. Again,
the question how the assumed duty was arrived at may need consideration.
It may have been arrived at by taking the duty figures of some existing
canal, based on discharge figures which were the result, not of observed
but of calculated discharges, and if the calculations were based on a
value of N which experience has proved to be wrong, a correction is
obviously needed. Many mistakes of the kinds indicated above have been
made, not perhaps in the case of a project which has been recently got
up and is then quickly carried out in its entirety, but in one which is
carried out slowly or after a long period has elapsed or in one which
consists of extensions of an existing system. So great, however, is the
elasticity of a channel--by which is meant its capacity for adapting
itself to varied discharges, a small change in the depth of water
causing a great change in the discharge--and so considerable has been
the uncertainty as to the real duty to be expected, that any mistakes
made have not usually resulted in any serious trouble.

[Illustration: BIFURCATION AT TAIL OF CANAL.

The Distributaries have Gates and Winches.

_To face p. 41._]

It has been stated (CHAPTER I, Art. 2) that it is not desirable to let
one channel tail into another. In old canals a distributary used
sometimes, after running parallel to a canal, to be brought back towards
it and tail into it. The advantage of this was that the distributary had
not to be made very small towards the tail and that, if the demand
abruptly ceased, the distributary was not likely to breach. The
principle was, however, essentially bad. The lower part of the
distributary was obviously too near the canal and not centrally
situated as regards the irrigated strip. The portion at the extreme tail
was superfluous. Again, whatever volume of water was carried through the
distributary and back into the canal, was needlessly detached instead of
being kept in bulk. Moreover the duty of water on such a distributary
cannot be ascertained without a tail gauge and the observation of
discharges at the tail. There are similar objections to one distributary
tailing into another. Each should be separate and distinct.

A major distributary is one whose discharge is more than 40 c. ft. per
second. It may be as much as 250 c. ft. per second. A branch, as soon as
it reaches a point where its discharge becomes only 250 c. ft. per
second should be considered as a major distributary. A minor
distributary is one whose discharge is from 8 to 40 c. ft. per second. A
minor distributary is nearly always a branch of a major distributary.
There are instances of “direct minors,” i.e., minors taking off from
canals or branches. Such a minor, unless its discharge is a large
fraction of that of the canal which supplies it--and this can seldom be
the case--is objectionable because the petty native official who has to
see to the regulation of supplies can manipulate the supply easily and
without detection, and the number of persons irrigating from it being
small, he can make private arrangements with them. On the Sidhnai Canal
there are some half-dozen distributaries each of which had one or two
minors which took off close to the head of the distributary. The people
who irrigated from the minors managed to get the heads shifted and taken
off direct from the canal, on the ground that, the water level in the
canal being higher than in the distributary, there would be better
command and less silt deposit. The irrigation on all these minors ran up
to a figure far in excess of what had been intended, to the detriment of
lands further down the canal. The minor heads have all been
retransferred to the distributaries, the difficulty as to command being
got over, as it should have been at first, by constructing weirs in the
distributaries. The fall in the water surface at the distributary head,
i.e., the difference between the water level in the canal and that in
the distributary downstream of its head but upstream of the weir, is
quite trifling or even inappreciable.

In some of the older Indian canals it was the custom to place the heads
of distributaries, not just above a fall but several hundred feet above
it, the idea being that the distributary then received less silt. This
practice has now been discontinued. There is no valid reason for
following it.

The question whether, when a channel crosses a road on the skew, a skew
bridge should be constructed or curves introduced into the road or
channel, is one which requires some consideration. As far as possible
the lines of channels should be fixed so as to cross important[10] roads
on the square or with a small angle of skew. In the case of main canals
or branches, the introduction of special curves is generally out of the
question, but if the road is not straight something can be done by
shifting the line one way or the other. In the case of “major”
distributaries, curves can to some extent be introduced. In the case of
“minor” distributaries it is often possible to curve the channel, with a
radius of say 500 feet, so that it will cross the road at right angles.
There is very little objection to a skew bridge if the angle of skew is
not great. The angle of crossing having been made as near to 90° as
possible, the bridge can be made skew though not necessarily so much
askew as the road. Slight curves can be introduced into the road. When
the road is made askew, a bridge on the square involves at least three
considerable curves (Fig. 7) and the taking up of extra land. It also
causes, in perpetuity most likely, a more or less inconvenient and
unsightly arrangement and one which, in most countries, would not be
tolerated. When the angle of skew is not great, it is best to introduce
no curve at all into the road. In the case of a “village” road, which
may be more or less undefined and liable to be shifted, the difficulty
about land may not be great, but even in this case the angle of crossing
should, if possible, be kept near to 90°, especially in the case of
minors, and where curves have to be introduced into the road they should
be suitable ones. Abrupt angles are not only unsightly but are unfair to
the cart drivers. The crossings of village roads by the minors of a
certain great modern canal have been stigmatised as “hideous.” Indian
canals can afford to do work properly.

  [10] In India “district” and “provincial” roads.

[Illustration: FIG. 7.]


4. =Remarks on Distributaries.=--Before a canal system can be properly
designed, it is necessary to determine certain points in connection with
the working of the distributaries. A distributary is intended to
irrigate a certain kharif area. Its average kharif supply is determined
from the assumed kharif duty. It generally runs full in the kharif but
not always. In a very dry tract such as the Montgomery district of the
Punjab, the demand is so great and so steady that a distributary
practically runs full through the greater part of the kharif. In such a
case the canal or branch must be so designed that it can keep all
distributaries full at the same time. Its F.S. discharge will be the sum
of all the F.S. discharges of the distributaries plus the losses of
water by absorption.

But in other cases, especially if the rainfall is considerable, a
distributary does not require its full supply, either all through the
kharif or for long at a time. An estimate must then be made of what it
will require. It may be estimated that its requirements will be met if,
during the period of greatest demand, it is closed for two days out of a
fortnight and receives full supply for the remaining twelve days. In
this case, since the various distributaries need not all be closed on
the same days, the canal or branch can be so designed that it will carry
a full supply equal (after deducting losses) to ⁶⁄₇ths of the aggregate
full supplies of the distributaries. In other cases the fraction may be
³⁄₄ths. It is likely to be lower the greater the rainfall of the
district. Even in the case when the distributaries run full through
nearly the whole of the kharif, there will be periods when they only run
with about ³⁄₄ths full supply. If full supply were run at such times,
many of the outlets would discharge more water than was required, the
cultivators would partly close them, and breaches in the banks of the
distributary might result. Thus the water level of a distributary must
always be so arranged that it will have a good “command” when it is
running with about three-fourths of the full supply discharge. The water
level with ³⁄₄ths full supply is generally ·5 to ·75 feet below the full
supply level but it should be calculated in each case. Generally it will
be correct to make the water level, when ³⁄₄ full supply is run, about 1
foot above the high ground traversed by the distributary, excluding any
exceptionally high portions of small area. A more exact method is given
in Art. 9. The greater the proportion of the culturable area which is to
be irrigated, the less should be the area of any high land which is
excluded. The F.S. levels of the distributaries at their off-takes must
be settled in accordance with the foregoing remarks, and these F.S.
levels must be entered on the plan. Neglect to thus fix the F.S. levels
of distributaries before designing the canals has frequently led to
trouble.

The head needed at a bifurcation in order to get the supply into a
branch or distributary is always small unless the velocity is high. For
a velocity of 3 feet per second the head required is only about ·16 ft.,
for 2 ft. per second ·1 ft.

On an Inundation Canal which has no weir across the river, the mean
supply downstream of the regulator (which is built a few miles down the
canal lest it should be damaged by the shifting of the river) is, as has
been mentioned, about half the full supply. The command in such canals
is not generally very good. A distributary can often obtain only mean
supply and it should be designed so as to command the country when it is
carrying mean supply. A detailed description of Inundation Canals in
Northern India, is given in _Punjab Rivers and Works_.

Let M, F, m, f, be the mean and full supply discharges at the heads of a
canal and of an average distributary on it and let the number of
distributaries be n. It has been seen (Chap. I. Art. 6.) that M = ·8F
about. Let k be the proportion of the supply lost by absorption in canal
and branches. Then n m = (1 - k) M = ·8 (1 - k) F. If the distributaries
all run with full supplies--at the time of greatest demand--for 4 days
out of 5, then,

  nf = 1·25 (1 - k)F

  f   1·25
  - = ---- = 1·56
  m    ·8

Since k depends on the wetted area, it is not likely to be so great for
F as for M, but the above gives a general idea of the ratio of the full
kharif discharge to the mean kharif discharge. On a large canal the
circumstances of the distributaries will not all be similar. Some will
run full for a greater proportion of their time than others. They can be
divided into groups and the ratio of the full to the mean supply
calculated for each group. The mean supply is, as above stated, obtained
from the area to be irrigated, and the duty as estimated at the
distributary head.

At one time a system was introduced of making distributaries of large
size with the idea of running them for short periods. One reason given
for abandoning this arrangement, was that there was a tendency to run
such a distributary for too long. This reason is not very intelligible.
It would be applicable to any distributary which was not intended to be
run without cessation. The result would be that some other distributary
would be kept short of water and this would imply extremely bad
management. The chief reason against such a distributary is the greater
cost of its construction. It would effect a saving of water. The ratio
of the discharge to the wetted area would be high, though this would be
to some extent neutralized by the greater frequency of closures, since,
when water is admitted to a dry channel, the absorption is at first
great. There would also be some difficulty in the distribution of the
water because of the short period for which it would remain open. It
will be seen (Chapter III. Art. 5), that it is desirable to open and
close always at the same hour of the day. An ordinary distributary might
run for 11 days out of 14. One of double the size could not conveniently
be run for 5¹⁄₂ days. A distributary can always be enlarged if
necessary, but if made too large it is extremely difficult to make it
smaller.

It was also, at one time, usual to make minors, when there were several
on a distributary, of large capacities so that they ran in turns. The
preceding remarks apply to this case. The system has been abandoned.


5. =Design of Canal and Branches.=--The apportioning of discharges to
the various channels having been effected as described in Art. 2, the
designing of the canal and branches is proceeded with. Rough
longitudinal sections of all the lines are prepared by means of the
contour map, the ground levels being shown at intervals of one foot--or
whatever the vertical distance between the contours may be--and the
horizontal distances obtained from the map by scaling.

On these longitudinal sections the lines proposed for the bed and F.S.
levels are shown reach by reach and also the mean velocities and
discharges.

The laws of silting and scouring and the principles on which channels
should be designed are fully gone into in _River and Canal Engineering_.
It is there explained that, for a channel of depth D, there is a certain
critical velocity, V₀, which just prevents the deposit of the silt,
consisting of heavy clay and fine sand, found in Indian rivers--this
silt enters the canal in such immense quantities that the canal silt
clearances would be impossible if much of it was deposited in the
channels--that sand of grades heavier than [·1] may deposit in the head
of a canal and well nigh threaten its existence, that the clear water
entering the canal in winter may pick up and carry on some of the sand
but that proper steps for preventing the deposit in the canal can be
taken at the headworks. This last question has been referred to in Art.
1. The following additional rules for designing canals in Northern India
are chiefly taken from those given by Kennedy in the explanatory notes
to his Hydraulic Diagrams, which are in use in the Irrigation Branch in
Northern India.

  (1) Near the hills where the bed is of shingle the velocity may exceed
  V₀. A few other soils will stand 1·1 V₀.

  (2) In ordinary channels any excess over V₀ will give much trouble
  lower down.

  (3) In the first four or five miles of a distributary, V₀ should be
  allowed and gradually be reduced to ·85 V₀ at the tail, the gradient
  being reduced if convenient, while a minor or branch distributary
  should have less than V₀ at its off-take and still less at the tail.
  The sand is drawn off by the outlets and in the lower part of a
  distributary it is often non-existent.

  (4) If there is efficient silt trapping at the head of the canal any
  figures arrived at by the preceding rules should be multiplied by ·9.

  (5) In the case of a canal having its head far from the hills, the
  sand is finer and any figures arrived at as above may be multiplied
  by, perhaps, about ·75, but further experience is needed to decide
  this.

  (6) If the soil is very poor, especially if the depth of water is more
  than 6 or 7 feet, the velocity should be less than V₀--say ·9 V₀--so
  as not to cause falling in of the banks. Depths of more than 9 or 9·5
  feet should, as far as possible, be avoided for the same reason.

  (7) At a bifurcation, one branch channel may have no raised sill, and,
  owing to its smaller depth, it may draw off no surface water and get
  an undue share of rolling sand. Its velocity should be greater than V₀
  and that of the other branch be less than V₀.

  (8) At such a bifurcation it may be necessary, during times of low
  supply, to head up the water in the main channel and some silt may
  temporarily be deposited in it. When the heading up ceases, the silt
  is scoured away but it mostly goes into the branch whose bed level is
  the lower. It is best to design such bifurcations so that the sill
  levels of the two branches are equal and, if possible, so that their
  bed levels are equal.[11] Otherwise the channel which is likely to get
  most silt should have the steeper gradient.

  (9) Any existing well established régime should not be tampered with.

  [11] Appendix A in _River and Canal Engineering_ deals with some
  instances of fallacies in questions concerning flow in open streams.
  An extract from it describing a remarkable divide wall recently
  constructed at the head of the Gagera branch, Lower Chenab Canal, is
  given in Appendix A of this book.

Experience shows that in designing Irrigation Channels in the plains of
India in accordance with Kennedy’s figures, the maximum ratio of bed
width to depth of water is as follows:--

  Discharge, c. ft. per second   10    25    100    200    500    1,000
  Ratio                         3·5     4    4·5     5      6       6

The actual gradients of the canals generally range from about 1 in 8,000
for a main canal to 1 in 2,000 for the tail of a distributary, but near
the head of a canal where the bed is of boulders and shingle, the
gradient may be as steep as 1 in 1,000.[12] The velocity in this last
case may be 5 feet per second but generally it is not more than 3 or 4
feet per second in canals and branches, and 1 to 2 feet per second in
distributaries.

  [12] On the Upper Jhelum Canal, 1 in 970.

In designing the channels, N, in Kutter’s co-efficient, may be taken as
·0225 or ·020, according to judgment. For new and smooth channels ·020
is generally correct. A channel generally becomes rougher by use but
sometimes it becomes smoother. Cases have occurred in which N has been
found to be ·016. This question is discussed in _Hydraulics_, Chap. VI.

The bed width of a canal is reduced, where a distributary takes off, in
such a way that when the canal and distributary are both running full,
the depth of water in the canal continues to be uniform and the flow to
be uniform. When the distributary is closed there is heading up in the
canal upstream of the off-take, but not enough to make any appreciable
difference unless the capacity of the distributary is a large fraction
of that of the canal and even then no harm is likely to result.

The preceding rules and principles being taken into consideration, the
channels are designed. The bed levels, gradients and depths are so
arranged as to give the velocities suited to the soil and to maintain
the proper relation of depth to velocity. The bed width is arranged so
as to give the proper discharge. The full supply level of the canal and
branches has also to be so arranged that it shall be higher, at each
distributary off-take, than the full supply level of the distributary.
It is desirable to be able to give a distributary its full supply even
when the canal is low. Generally the slope of the country along any line
is greater than would be suitable for the bed, and “falls” are
introduced. The off-take of a distributary is generally just above a
fall and there is generally an ample margin between its F.S. level and
that of the canal. The discharge of the canal during the greater part of
the rabi may be only about half the full supply. This discharge should
be estimated and the water level corresponding to it calculated and
shown on the longitudinal section. If possible the levels should be so
arranged that even with its least supply the water level in the canal
will enable full supply to be given to a distributary. If this cannot
otherwise be managed it may be necessary to construct a regulator in the
canal below the head of the distributary so that, during low supplies,
the water can be headed up. It has been stated in _River and Canal
Engineering_, Chapter IV., that such heading up, if temporary, is not at
all likely to cause silt deposit in the canal. The designing of the
distributaries is not proceeded with at this stage.

Since no irrigation is usually done directly from the canal and
branches, they are designed without any particular connection between
the level of the water and that of the country traversed. Dangerously
high embankments are of course avoided as far as possible. The bed is
designed at such a level that the excavation and embankment at any place
will be, as nearly as possible, equal. Land in India is cheap. When the
excavation exceeds the embankment the balance is made into a spoil bank.
When the excavation is less than the embankment the balance is got from
borrow-pits.

The side slopes of channels in excavation are generally 1 to 1, in
embankment 1¹⁄₂ to 1. The sides of channels of small or moderate size
usually become about ¹⁄₂ to 1, or even vertical, by the deposit of silt
on the slopes. This reduction of area is allowed for in the design i.e.
the bed width is so designed that the channel will carry the required
discharge, not with the side slopes as executed, but when they have
become ¹⁄₂ to 1. In large canals however the sides do not always silt up
but rather tend to fall in. When this is expected to occur the allowance
above described is not made. Berms are left so that if any part of the
sides fall in, the bank will not also fall in. The berms also allow of
the channel being widened if that ever becomes necessary. Type sections
are given in Figs. 8 and 9.


6. =Banks and Roads.=--Figs. 8 and 9 show the banks and spoil.

[Illustration: FIG. 8.]

[Illustration: FIG. 9.]

The scale is 6 feet to an inch. The depth of water, in this particular
case, is 7 feet, and the bank, excluding the small raised bank, 2 feet
above the water. The inside edge of the bank, where the small raised
bank is shown, is kept parallel to the canal for a considerable
distance. Its position is got by drawing a line, shown dotted, at,
generally, 1¹⁄₂ to 1. The embanked part of the slope is actually made at
1¹⁄₂ to 1, but the excavation is at 1 to 1, so that a berm is left. The
width of this berm of course varies as the depth of digging varies. If
there is likely to be much falling in of the sides the berm can be made
wider, the dotted line starting, not from the edge of the bed, but from
a point further in. On an inundation canal in sandy soil the berm may be
20 feet wide. In figure 8, the inside slope above the berm is supposed
to have silted up to a slope of 1 to 1. In cases where it is expected
the whole inside slope will silt to ¹⁄₂ to 1 the dotted line, to give
the edge of the bank, can be shifted towards the channel so that the
berm at the ground level when the channel is excavated will be very
small for the minimum depth of digging. There is no need for the inner
edge of the bank to run parallel to the canal for great distances. Its
position can be shifted whenever suitable and the width of the berm at
ground level varied. This prevents the occupation of a needlessly great
width of land. It used at one time to be not unusual to make a bank with
a berm on the land side, similar to that formed by the spoil in Fig. 8,
but at about the level of full supply in the canal. The principle is not
a good one. Salient angles are liable to be worn away. If earth has to
be added to a bank to strengthen it, the whole can be widened or the
rear slope flattened. The roadway is shown 18 feet wide, which is nearly
the maximum. For the drainage of rain water it has a transverse slope,
away from the canal, of about 1 in 50. The small raised bank on the
canal side is to give safety to wheeled vehicles. It is provided on the
patrol bank[13] on main lines and places where there is much traffic or
where there is plenty of width of bank to spare. When the ground level
is, for a considerable distance, above the proper bank level--which is
at a fixed height above the F.S. Level--so that the road and its
side-drain have to be cut out, much earthwork can be saved by allowing
them to be at a higher level and, in the case at least of the non-patrol
road, giving the road a reduced width.

  [13] A canal has an unmetalled driving road--called the “patrol road”
  or “inspection road” on one bank. This road is reserved for the use of
  officials. Otherwise, it would soon be cut up and worn away, and the
  cost of repairs would be excessive. The patrol road should be on that
  bank which is, in the morning (the time when inspections are usually
  made) in the shade of trees planted on the landward side. Trees are
  not usually planted near the water edge as they are sometimes blown
  down. In Northern India the canals generally flow in a southerly
  direction, so that the left bank is best for the patrol bank. On the
  other bank there is a bridle road which is open to the public. Near a
  rest house--unless there is a bridge actually at the place--the patrol
  road should be on the same bank as the rest house. It can if necessary
  cross at the first bridge. Frequently there is also on one or both
  sides of the canal a “boundary road,” which is open to the public,
  along the toe of the outer slope. Along a distributary there may be a
  boundary road on one side. It is generally the only road which can
  take wheeled traffic, and in this case it should be reserved for
  officials unless money is provided to keep it always in repair.
  Officials have to be on tour for weeks or months at a time, and in all
  weathers. Their baggage carts also have to precede and follow them.
  Anything which facilitates their touring about and seeing things for
  themselves is, in India, most desirable. At a watercourse crossing the
  boundary road along a distributary should be taken by a curved incline
  up on to the bank and down again. Thus not only is the cost of a
  culvert saved, but any touring official who is driving obtains a view
  of the channel which he cannot get from the boundary road.

[Illustration: FIG. 10.]

In shallow digging, the plan of setting back the banks (Fig. 10) and
letting silt deposit as shown by the dotted lines, is one which should
be followed much oftener than it is. It not only gives eventually a very
strong bank, but it enables the borrow pits, from which the earth for
the banks is got, to be dug inside the banks. Outside borrow pits,
besides being a source of expense, owing to compensation having to be
paid to those in whose land they are dug, cause great areas of hollows
which are not only unsightly, but are often full of stagnant water and
are thus a fruitful source of mosquitoes and malaria. Insufficient
attention has hitherto been paid to this matter.

In designing each reach of a canal or branch, type cross sections should
be drawn out for several different depths of digging, _e.g._, one for
very shallow digging, _i.e._, where the bed is little, if at all, above
the ground level, one for deep digging where the ground is higher than
the water level, and one for the “balancing depth,” where the area of
the channel excavation is equal to the earth required for the banks. In
calculating the earthwork the sectional area of the digging or of the
embankment is taken, whichever is the greater.

The proper width and height of bank for any channel depends partly on
the maximum depth of water in the channel, and partly on the discharge.
Given a depth of water of say 8 feet, a breach will obviously be more
disastrous with a great volume of water than with a small volume. The
following statement gives some figures suitable to the rather light and
friable soils of Northern India, but the question is largely one of
judgment. Generally a low and rather wide bank is preferable to a higher
and narrower one. If a road, with or without the small raised bank next
the canal, is required, special widths can, of course, be arranged for.
A 14-foot bank is required for a driving road.

  ------------+--------------+---------------+---------------
  Top Width of|Height of Bank|   Greatest    |   Greatest
     Bank.    | above F. S.  |  Admissible   |  Admissible
              |              |  Discharge.   |Depth of Water.
  ------------+--------------+---------------+---------------
      Feet.   |    Feet.     |C. ft. per sec.|    Feet.
       20     |     2        |    12,000     |     12
       18     |     2        |     8,000     |     12
       16     |     2        |     5,000     |     11
       14     |     2        |     3,000     |     10
       16     |     1·5      |     2,000     |      9
       14     |     1·5      |     1,500     |      9
       12     |     1·5      |     1,200     |      8
       10     |     1·5      |     1,000     |      7
        9     |     1·5      |       700     |      6
        8     |     1·5      |       500     |      5·5
        7     |     1·5      |       400     |      5
        6     |     1        |       300     |      4·5
        5     |     1        |       200     |      4
        4     |     1        |       100     |      3·5
        3     |     1        |        50     |      3
  ------------+--------------+---------------+---------------

The spoil in Fig. 8 is shown at a different level from the bank proper,
as it should be to give a neat straight edge to the bank. The width of
the spoil may vary every chain. In Fig. 9 the spoil is raised to avoid
taking up too much land. The spoil presents the best appearance when its
height is kept uniform for as long a length as possible, the width
varying according to necessity, When the height has to be altered, the
change should be made by means of a short ramp. When the spoil is higher
than the road, gaps in it are left at intervals so that rain water can
pass away. When the spoil is heavy for a very short length it can, in
order to avoid a short and unsightly heap, which would result from the
adoption of the section shown in Fig. 9, be placed as in Fig. 8, some of
it being led askew.

The small channel shown outside the bank in Fig. 8 is a watercourse for
enabling trees to be grown. It has, of course, to be graded, and it may
be in cutting or in embankment. If any silt clearances of the canal are
likely to be necessary, the watercourse must be set back to allow room
for the spoil. Such spoil, if sandy, is to a large extent washed down or
blown away and does not accumulate to anything like the extent that
would be expected.[14] Moreover the spoil can extend onto the
watercourse when the trees have grown big, and no longer need watering.
Outside the watercourse is shown the boundary road and the land boundary
pillar. The small channel in Fig. 9 is a drain for rain water. It can be
used as a plantation watercourse if the water is lifted.

  [14] This fact has been quoted (_The Pioneer Mail_, “Silt,” 8th March,
  1913) as showing that the silt supposed to be cleared is not really
  cleared. This may be the case to some extent, but shortage of spoil is
  little proof of it.

Where there is no spoil, some extra land, perhaps 20 feet on either
bank, is usually taken up for getting earth from for repairs.


7. =Trial Lines.=--The proposed lines of channel, determined as
explained in Art. 5 should next be laid down on the ground. A line
should consist of a number of straight portions. The curves should not
be put in. Trial pits should be dug at intervals. Some defects in the
line may at once become apparent because the contour map, owing chiefly
to the lines of levels having been taken a considerable distance apart,
is not perfect. A line may pass through a patch of very high or very low
ground or too near to some building or other object with which it is
desirable not to interfere. Alteration may be desirable at a drainage
crossing or at the off-take of a branch. The lines should be corrected
where necessary. Sometimes the corrections may be very considerable.
Allowance can be made for the alterations which will occur when the
curves are laid out. Where there is doubt as to which line is the best,
trial pits may be dug to obtain further information regarding the soil.

The line should now be levelled, careful checks being made, a
longitudinal section of it prepared and the proposed bed, bank and F.S.
level shown. The ground levels ascertained by levelling the line, are
certain to disagree, to some extent, with the contour lines. The latter
were got only by inference from the levels of points in the survey
lines, and they should be corrected in accordance with the fresh levels
now available. If the line does not seem to be the best that can be got,
a fresh line can be marked on the plan and the above procedure repeated.


8. =Final Line and Estimate.=--As soon as the best line seems to have
been found, a large scale plan of the country along its course should be
made by taking bearings or off-sets from points in it to the various
objects and noting where the line cuts them. On this plan will be shown
the exact alignment, the curves being put in and the straight portions
slightly shifted where necessary so that the line may pass at a proper
distance from any buildings or other objects. But before this procedure
is carried out, or while it is being carried out, the estimate for the
work can be prepared from the longitudinal section already taken. Such a
section is of course amply sufficient for a “project estimate,” in which
only approximate figures are given, and it is quite near enough for any
estimate. In the case of small works which have often to be executed
with great promptitude, lamentable delays have occurred owing to the
engineer deferring the preparation of his estimate till he had got the
line exactly fixed. Moreover there is a chance of the labour being
thrown away in case the sanctioning authority directs any change in the
alignment to be made.

In the case of a large scheme, a project estimate is prepared. In this
the earthwork and the area of land to be occupied are calculated pretty
accurately. Designs and estimates are also prepared for the headworks
and for the chief regulators. For works of which there are to be many of
one type--bridges, falls, distributary heads and small drainage
syphons--the cost is arrived at from lump sum figures, one drawing of
each kind being submitted as a type. The distributaries are
approximately estimated at mileage rates. In the case of a small scheme
everything is estimated in detail except perhaps the distributaries or
some of them.

[Illustration: CANAL WITH BRIDGE AND DISTRIBUTARY HEAD.

The Head has Gates and Winches.

_To face p. 61._]


9. =Design of a Distributary.=--A distributary is a canal in miniature
and, like a canal, it may have branches. It has masonry bridges, falls
and drainage syphons. It has, as already mentioned, a masonry regulator
at its head. At the off-take of any branch or distributary there is a
regulator in the head of the branch. If the branch takes off a large
proportion of the water there is a double regulator. A distributary
gives off watercourses as a canal gives off distributaries. The
watercourses belong to the people and not to Government and they are
cleared and maintained by the people. Each watercourse has a masonry
head known as an “outlet” (Fig. 11). The outlet is the point where
the water passes from the hands of Government officials to those of the
cultivators. The outlet is of masonry and its opening is not adjustable
but is fixed in such a way that its discharge, when the distributary is
full, bears, as nearly as can be arranged, the same ratio to the F.S.
discharge of the distributary as the area intended to be irrigated by
the watercourse bears to that intended to be irrigated by the
distributary.

[Illustration: FIG. 11.]

The floor of the outlet is level with the bed of the distributary. It
thus draws off rolling sand which might otherwise accumulate in the
distributary. Small outlets are made of earthenware pipes, about ·4 feet
in diameter, laid in concrete. Two pipes, or three, may be laid side by
side. If more than three would be required, a masonry opening is
adopted. The discharge through an outlet, is generally 2 to 5 c. feet
per second per square foot of outlet area, and the head ·1 to ·5 feet.

For the tract of country allotted to any distributary, a contour map is
prepared on a fairly large scale, say 4 inches to a mile. On the map
the line is laid down and a rough longitudinal section, showing the
ground level, is prepared as in the case of a canal.

It has already been stated (Art. 4) that a distributary is so designed
that its water level, when three-fourths of the full supply is run,
shall be well above the level of most of the ground along its course. In
other words it should have a good command. A good rule is to allow a
fall of ·5 feet from the level of the water in the distributary to that
in the watercourse, a slope of 1 in 4,000 for the water flowing along
the watercourse, and a fall of ·3 feet for the water at the tail of the
watercourse to the level of the ground. This last level is, like the
other ground levels, taken from the contour map. This procedure, in
short, consists in making the water level of the watercourse at its head
govern that of the distributary, just as the water level in the
distributary at its head was made to govern that in the canal.

The enlarged contour map of the distributary area shows, among other
things, the boundaries of the lands belonging to each village. Generally
a watercourse supplies water to only one village. When, however, a
village is far from the distributary, its watercourse has to pass for a
long distance through other villages and it would be wasteful of water
to have two separate watercourses. In such cases one watercourse may
serve two villages or more. When a village is near to the distributary
and its land extends for a long distance parallel to the distributary,
it may have several watercourses for itself alone. A watercourse can
generally be most conveniently dug along the boundary line of two
villages, or there may be some other line which the people particularly
desire.[15] Subject to, or modified by, these considerations a
watercourse is designed to run on high ground like a distributary.

  [15] They also frequently wish the “chak”--the area irrigated by a
  watercourse--so arranged that two men who are “enemies” shall not be
  included in the same “chak.” This condition can be complied with only
  up to a certain point. Arrangements may be modified but not in such a
  way as to upset the proper rules.

[Illustration: CONTOUR MAP (PART) AND LINE OF DISTRIBUTARY.

The scale is 1 inch to 2 miles. The contour lines at 1 foot intervals
are shown dotted, the roads by double lines. The line of the
distributary, in order to follow the ridge of the country, would have
gone more to the left of the plan near the village. The shifting of the
line to the right brings it nearer to the centre of the irrigated
tract--supposed to be the whole area shown--and enables a single bridge
to be built at the bifurcation of the two roads. Suitable lines for main
watercourses are shown in thin firm lines. It is assumed that the
command is sufficient to enable the watercourses to run off at the
considerable angles shown.

_To face page 63_]

The great object is to reduce the total length of channels, _i.e._,
minors and watercourses. No watercourse can be allowed to run alongside
of or near to another. It may run alongside a canal or distributary when
really necessary to gain command but not otherwise. The longer the
watercourse the larger the chak. The discharge of an outlet may be
anything up to 4 or 5 c. feet per second. This limits the size of a
chak. If a chak is too big it can be split up or a minor can be
designed. Very small chaks are to be avoided, but it is difficult to fix
a minimum size. The irrigation boundary of the distributary, as fixed in
the project, is shown on the map but in practice it will not be exactly
followed. For various reasons the boundaries of a chak may run somewhat
outside it or stop short of it.

Where a distributary gives off a minor and there is a double regulator,
watercourses should, as far as possible, be taken off from one or other
of the branch channels and not from upstream of the double regulator.
Otherwise, irregularities are likely to occur, both of the regulators
being partially closed at the same time--a thing which is never
necessary in legitimate distribution of the supply--in order to head up
the water and increase the discharges of the outlets.

A watercourse nearly always gives off branches and generally a system of
turns is arranged by the farmers among themselves, each branch in turn
taking the whole discharge of the watercourse for a day or part of a
day, the other branches being closed by small dams of earth. To irrigate
a field alongside the watercourse a gap is cut in its bank. For fields
further away, smaller channels run off from the watercourses at numerous
points. Several gaps and several field channels may be in flow at one
time, and there is a dam in the watercourse below the lowest one.

Occasionally, on an old canal, one watercourse crosses another, the
lands irrigated being at different levels, but such crossings do not
often occur in systems of watercourses laid out according to modern
methods. They are, however, quite legitimate.

The lines of the main watercourses are sketched on the map, their
irrigation boundaries shown on it, and F.S. discharges allotted to them
according to the areas which are to be dependent on them. In order that
this may conveniently be done the “full supply duty” or “full supply
factor” for the distributary is obtained. It bears the same ratio to the
ordinary duty that the mean supply bears to the full supply. The total
of the F.S. discharges of all the watercourses should, with an allowance
for loss by absorption in the distributary, be the same as the F.S.
discharge of the distributary. If the results are very discrepant it
shows that the sizes of the outlets need revision. Possibly they may all
be too large.

In “colonization” schemes where a canal is constructed to irrigate waste
lands--which are the property of Government and which are divided into
square blocks and given out to colonists--Government has complete
control of the watercourse system, and can arrange it exactly as
desired, but in other cases landowners often strenuously oppose the
passage of watercourses through their lands. Compulsory procedure
according to legal methods is tedious, but the practical rule is not to
let anyone have water until any watercourses which are to pass through
his land have been not only agreed to but constructed.

In ordinary cases Government possesses no power as to the precise line
on which a watercourse is dug. It fixes the site of the outlet and
assigns certain land to it, and sketches out the line of the
watercourse. If the people choose to alter the line they can do so, but
great alterations in the main watercourses are not generally feasible.

The positions of the outlets[16] having been settled after discussion
with the cultivators, a table is prepared showing the chainage of the
outlets, the probable head or difference between the F.S. level of the
distributary and of the watercourse, and the F.S. discharge. From this
the sizes of the outlets are calculated and shown in another column. If
the length of the outlet barrel is not more than 5 or 6 times the
diameter--in the case of a barrel whose cross section is not round or
square, the mean diameter--the discharge can be calculated as for a
“short tube,” but if longer the formula for flow in pipes should be
used, allowance being, of course, made for the head lost at the
entrance. The outlets generally consist at first of wooden “shoots” or
long tubes, rectangular in cross section. This is because, after they
have been tested by a year or two years’ working, the sizes nearly
always require adjustment and the cultivators often wish to have the
site shifted.

  [16] The positions can be slightly altered by the Engineers for any
  sufficient reason.

[Illustration: FIG. 11.]

The uncertainty as to the proper size of an outlet is due to several
causes. If the command is very good there may be a clear fall from the
outlet into the watercourse. In this case the discharge depends only on
the depth of water in the distributary, and is known pretty accurately.
But ordinarily the outlet is submerged, and its discharge depends on the
difference between the water levels in the distributary and in the
watercourse. The latter level is not fixed. The cultivators can lower
it, to an extent which depends chiefly on the distance of the fields
from the distributary, by deepening or widening the watercourse. In this
way the discharge of the watercourse is increased except when a dam is
temporarily made in it for the purpose of irrigating any comparatively
high land. This uncertainty as to the discharge can in some cases be got
over by building a cistern (Fig. 11). This has the same effect as
raising the level of the barrel, the real outlet being no longer
submerged, and the discharge depending on the depth of the crest of the
overfall below the water in the distributary. But such cisterns add
greatly to the cost of an outlet, and they can only be adopted when
there is good command. A great cause of uncertainty as to the proper
size of an outlet is the variability of the duty of the water on the
watercourse. The soil may be clayey or sandy, the watercourse may be
short or long, the crops grown may be ordinary ones or may be chiefly
rice, which requires three or four times as much water as most other
crops, and the cultivators may be careful or the opposite. Again, the
people may, if the outlet gives a plentiful supply, often keep it
closed, but there is no record of such closures nor would the people
admit that they occur. These causes may all operate in one direction--on
a whole distributary this cannot happen to the same extent--and thus
enormous differences in duty may occur. There is no way of arriving at
the proper size for an outlet except trial. Observations of the
discharges of the outlets are of very limited use. The discharge may
vary according to the particular fields being irrigated. Observations of
discharges will be useful in cases where the people complain, or when
the discharge is obviously much greater or much less than intended and
will in such cases enable temporary adjustments to be made, but by
placing a dam in a watercourse and turning the water on to a high field
near its head the people can make it appear that the discharge is only a
fraction of what it should be.

On any distributary there are generally some watercourses which have a
poor command, the head at the outlet being, say, ·1 ft. or even less.
Probably the irrigation is a good deal less than it should be. In such
cases the rules may be set aside and a liberal size of outlet given. The
size may be 2 or 3 times the calculated size. There is no harm in this.
The irrigation cannot increase much. Similar cases frequently occur on
inundation canals especially near the heads of canals or distributaries.

The construction of masonry outlets on a distributary is not usually a
final settlement of the matter. Further adjustments become necessary.
This matter will be dealt with in CHAPTER III.

On the older canals little or insufficient attention was given to the
question of the sizes of outlets. The sizes were far too great and, as
long as all the outlets in a distributary remained open, water could not
reach the tail. The distributary used to be divided into two or three
reaches and the outlets in the upstream reaches used to be closed
periodically. The closures had to be effected through the agency of
native subordinates and the system gave rise to corruption on a colossal
scale. The tail villages never obtained anything like their proper share
of water. The upper villages were over-watered and the soil was often
water-logged and damaged. Moreover, even if all concerned had the best
intentions, it was impossible to stop all leakage in the closed outlets,
except by making earthen dams in the watercourses, and great waste of
water resulted from this.

The water level of the distributary with ³⁄₄ full supply, designed so as
to be at least ·5 ft. above the water level in the watercourse heads--or
to be 1 foot above high ground if this simpler plan is adopted--is drawn
on the rough longitudinal section and also the line of F.S., falls being
introduced where desirable and the gradients, F.S. depths of water and
widths of channels being arranged, just as in the case of a canal, so as
to give the required discharges, velocities suited to the soil and a
suitable ratio of depth to velocity. The bed width of a distributary
decreases in whole numbers of feet. The decrease occurs at outlets but
not at every outlet. As the channel becomes smaller its velocity becomes
less and this necessitates, according to the laws of silting and scour,
a reduced depth of water. The height and width of the banks in the tail
portion of a distributary should be made rather greater than
elsewhere--regard being had to the depth and volume of the water--so
that breaches may not occur when the demand abruptly slackens. The
longitudinal section of a distributary should have horizontal lines for
showing the following:

  1. Datum         |5. Draw-off      | 9. Bank width   |13. Depth of
                   |                 |                 |    digging
  2. Bed gradient  |6. F.S. discharge|10. Height of    |14. Bed level
                   |                 |    bank         |
  3. Village       |7. Velocity      |11. F.S. depth   |15. Ground
                   |                 |                 |    level[17]
  4. Land width    |8. V₀            |12. Bed width    |16. Chainage[18]
  -----------------+-----------------+-----------------+----------------

  [17] Called “Natural Surface” in India.

  [18] Called “Reduced Distance” in India.

A specimen of a longitudinal section is shown in Fig. 12. It shows only
a few of the above items. In practice all would be shown, large sheets
of paper being used with all the lines and titles printed on them.

When a distributary is constructed the side slopes are made 1 to 1 in
excavation and 1¹⁄₂ to 1 in embankment. The sides usually silt up till
they are ¹⁄₂ to 1 or even vertical. The silting up to ¹⁄₂ to 1 is, as in
the case of a canal, allowed for in the designing. The berms are left so
that, if any part of the side falls in, the bank will not also fall in.
They also allow of widening of the channel. The remarks made in Art. 6
regarding the design of banks, apply to distributaries, especially large
ones.

On a distributary there is seldom much spoil. Where there is no spoil, a
strip of land, outside the bank and 10 feet wide, can be taken up on
either bank from which to obtain earth for repairs. On a minor the width
of the strip is sometimes only 5 feet.

[Illustration: FIG. 12.]

When a distributary passes through land which is irrigated from wells,
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 = -----
        3

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
register which the Subdivisional Officer has to inspect daily, is, in
any case, voluminous enough.

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

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

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

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

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

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


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

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

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

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

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

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

TABLE I--GAUGE AND DISCHARGE REGISTER.

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

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

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

Regarding the working out of delta month by month, not only are
discharges more or less doubtful, but the area irrigated is seldom
correct till near the end of the crop. However, the figures, towards the
end of a crop, may be useful. If delta on any distributary is higher
than is usual on that distributary, it may be desirable, if the supply
in the whole canal is short, to reduce the supply to that distributary
somewhat, but this remedy can be properly applied after the end of the
crop by altering the turns (Art. 5). Any steps in the direction of
altering outlets can only be taken after the end of the crop. Admitting,
however, that the working out of delta during the crop is useful, it can
be done by adding up the gauge readings for the month and taking the
average reading and the discharge corresponding to it. This is not quite
the same as the average of the daily discharges, but the difference is
small, and there would be a wholesale and most salutary saving in
clerical work. All the columns headed D could be omitted. The handiness
and compactness of the register would be vastly increased. The
discharges are only approximately known, and refinements of procedure
are unnecessary. The correction of the discharge table, by means of
observed discharges, once a month, can of course be effected without
booking the daily discharges.[27]

  [27] There should, in any case, be a special place in the gauge
  register for showing the discharge tables, with a note of the
  discharge observations from which the table was framed or in
  consequence of which it was altered.

Supposing the columns D to be retained the calculations of delta can be
made as shown in table II. the form being printed in the gauge book. To
facilitate the adding up of the discharges a line can be left blank in
table I. after each ten days, and the total for the ten days shown on
it. If the column D is not retained, the gauge readings can be added up.
The discharge corresponding to the mean gauge reading of the month,
multiplied by the number of days the distributary was in flow, gives the
figure to be entered in column 2 of table II.

The final working out of delta crop by crop is of course of the greatest
value. The point which needs attention is, as already remarked, greater
accuracy in the discharges. For reasons which have already been given
(CHAP. I., Art. 5, and CHAP. II., Art. 9) the values of delta on
different distributaries will never be the same, but the causes of high
values can always be investigated and, to some extent, remedied.

TABLE II.--CALCULATION OF DELTA FOR RABI, 1912-13, NANGAL DISTRIBUTARY.

  ------+------------+------------+---------+------+------------------
  Month.|  Total of  | No. of days|Irrigated| Delta|     Remarks.
        | discharges |  in flow.  | area up | up to|
        +------+-----+------+-----+ to date.| date.|
        | For  |Up to| For  |Up to|         |      |
        |month.|date.|month.|date.|         |      |
  ------+------+-----+------+-----+---------+------+------------------
        |      |     |      |     |  Acres  | Feet |
  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.          |
              |       |--------+--------+---------+--------------------+
              |       |        |        |         |Dimensions of barrel|
    Name and  |       |        |        |Sectional+----------+---------+
   description| Year  |Chainage|Material| area of |          |         |
   of outlet. |       |        |        | barrel. |  Width   | Height  |
              |       |        |        |(minimum)|          |         |
  ------------+-------+--------+--------+---------+----------+---------+
  Register no.|       |        |        |         |          |         |
              |1902-03|        |        |         |          |         |
      Name    |1903-04|        |        |         |          |         |
              |1904-05|        |        |         |          |         |
      Bank    |1905-06|        |        |         |          |         |
              |1906-07|        |        |         |          |         |
  Flow or lift|       |        |        |         |          |         |
  ------------+-------+--------+--------+---------+----------+---------+
  Register no.|       |        |        |         |          |         |
              |1902-03|        |        |         |          |         |
      Name    |1903-04|        |        |         |          |         |
              |1904-05|        |        |         |          |         |
      Bank    |1905-06|        |        |         |          |         |
              |1906-07|        |        |         |          |         |
  Flow or lift|       |        |        |         |          |         |
  ------------+-------+--------+--------+---------+----------+---------+
    Total }   |1902-03|        |        |         |          |         |
      of  }   |1903-04|        |        |         |          |         |
              |1904-05|        |        |         |          |         |
    {Village  |1905-06|        |        |         |          |         |
    {  Page   |1906-07|        |        |         |          |         |
  ------------+-------+--------+--------+---------+----------+---------+

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

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

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

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

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

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

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

  From.......................          To........................
  --------+------------+-----------+----------------------------------
  Name of |Commanded   |           |   Net Areas Irrigated in Acres.
  Village.|Culturable  | Detail.   +----+----+----+----+----+----+----
          |Area (Acres)|           |1902|1903|1904|1905|1906|1907|1908
          |            |           | -03| -04| -05| -06| -07| -08| -09
  --------+------------+-----------+----+----+----+----+----+----+----
          |            |  Kharif   |    |    |    |    |    |    |
          |            |  Rabi     |    |    |    |    |    |    |
          |            |  Total    |    |    |    |    |    |    |
          |            |Per cent of|    |    |    |    |    |    |
          |            |Culturable |    |    |    |    |    |    |
  --------+------------+-----------+----+----+----+----+----+----+----
          |            |  Kharif   |    |    |    |    |    |    |
          |            |  Rabi     |    |    |    |    |    |    |
          |            |  Total    |    |    |    |    |    |    |
          |            |Per cent of|    |    |    |    |    |    |
          |            |Culturable |    |    |    |    |    |    |
  --------+------------+-----------+----+----+----+----+----+----+----
          |            |  Kharif   |    |    |    |    |    |    |
          |            |  Rabi     |    |    |    |    |    |    |
          |            |  Total    |    |    |    |    |    |    |
          |            |Per cent of|    |    |    |    |    |    |
          |            |Culturable |    |    |    |    |    |    |
  --------+------------+-----------+----+----+----+----+----+----+----
          |            |           |    |    |    |    |    |    |
   Total  |            |           |    |    |    |    |    |    |
          |            |           |    |    |    |    |    |    |

The percentages of culturable commanded area irrigated by different
outlets will, as already explained, always show discrepancies. Any
special causes of low percentages, e.g. a large proportion of rice, can
be briefly noted in the register.

On inundation canals, and some others, the alignment and chainage are
liable to undergo alteration. In such cases it is best to adhere to the
original chainage until all the alterations in alignment have been
carried out.


5. =Distribution of Supply.= The question how the supply of a canal is
to be distributed when it is less than the demand, is not always very
simple. Suppose that the main canal, after perhaps giving off several
distributaries, divides, at one place, into three branches, A, B, and C,
whose full supply discharges are respectively 2,500, 2,000 and 1,500 c.
ft. per second. Suppose that the total discharge reaching the
trifurcation is expected to be, when at the lowest during the crop, only
2,200 c. ft. per second, instead of 6,000. It would be possible,
supposing the discharge tables to be fairly accurate, to keep all the
channels running with discharges proportionate to their full supplies,
but this would not be suitable. The water levels would not be high
enough to enable full supplies to be got into the distributaries, or at
least into some of them. Moreover, the running of low supplies causes
much loss by absorption. The plan usually adopted is to give each
channel full supply, or nearly full supply, in turn, and for such a
number of days that the turn of each branch will recur about once a
fortnight, that being a suitable period having regard to the exigencies
of crops, and having the advantage that the turn of each branch comes on
a particular day of the week, so that everyone concerned, and
especially the irrigating community, can remember and understand it.
Table V. shows how the turns in the above case can be arranged. The
figures show the discharges.

TABLE V.

  ---------+------+------+------
    DAY.   |   A  |   B  |   C
  ---------+------+------+------
     1     | 2,200|      |
     2     | 2,200|      |
     3     | 2,200|      |
     4     | 2,200|      |
     5     | 2,200|      |
     6     |      | 2,000|   200
     7     |      | 2,000|   200
     8     |      | 2,000|   200
     9     |      | 2,000|   200
    10     |      | 2,000|   200
    11     |   700|      | 1,500
    12     |   700|      | 1,500
    13     |   700|      | 1,500
    14     |   700|      | 1,500
  ---------+------+------+------
   Total   |13,800|10,000| 7,000
           |      |      |
  Correct  |      |      |
  discharge|12,800|10,300| 7,700
  according|      |      |
  to Full  |      |      |
  Supply.  |      |      |
  ---------+------+------+------

The orders given to the gauge readers in these cases are simple, namely
to give each branch full supply in turn, and to send the rest of the
water down the channel next on the list.

The number of days allotted to the larger branches are greater than to
the smallest because this will probably be simplest in the end, and also
because the number of distributaries on a larger branch is likely to be
greater, and the allotment to the distributaries is thus facilitated
somewhat. Each branch receives water in one period of consecutive days.
Any splitting up of the turn would be highly objectionable. It would
cause waste of water, and would give rise to much difficulty in
redistributing the supply among its distributaries. Each branch receives
its residuum turn before it receives its full supply turn. The advantage
of this is that water is not let into the channel suddenly. The total
supplies of A, B and C are in the ratio of 13·8, 10, and 7, and not, as
they should be 12·8, 10·3, and 7·7, but no closer approximation can be
got. If the number of days of full supply allotted to each branch is
changed, or if the residuum from C is given to B, instead of A, the
relative total discharges differ still more from what they should be.

If now the total supply is supposed to be increased to 2,700 c. ft. per
second, the discharges are as shown in table VI.

TABLE VI.

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

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

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

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

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

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

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

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

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

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

[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.

A Subdivisional Officer generally receives a steady stream of
applications from members of the irrigating community regarding--among
other matters--outlets or watercourses. Generally these applications are
made over to the zilladar to be reported on. In a large number of cases
the applicant states that the irrigation of his land or “holding” is not
satisfactory, or has fallen off, and sometimes he asks that it may be
transferred, wholly or in part, to another watercourse which he thinks
will give a better supply. In all such cases, and in some others, the
first requirement is a statement of the irrigation figures. The
irrigation register gives only the total for the watercourse. A printed
form should be prepared with spaces for showing the name of the
distributary, villages, watercourses, holdings and applicants concerned,
and the nature of the application. Below this is a form, prepared
somewhat as shown below. When this form is filled in, the state of
affairs can at once be seen and much trouble is saved. The zilladar
obtains the figures from the old field registers. The amount of detail
required as to the applicant’s lands depends on the nature of his
application. If it deals with only part of his land the other parts
should also be shown. He may for instance be giving a disproportionate
share of water to one part. If a transfer to another watercourse is
asked for, the figures for that watercourse are also required.

  -----------------+----------------------------------+--------+--------
   Areas in Acres. |      Applicant’s Holding.        |Total of|Total of
                   |-------+---------+---------+------| Water- |Distrib-
                   |       |         |         |Total.| course.| utary.
  -----------------+-------+---------+---------+------+--------+--------
  Culturable       |       |         |         |      |        |
  commanded.       |       |         |         |      |        |
                   |       |         |         |      |        |
  Net  {19...-19...|       |         |         |      |        |
  irri-{19...-19...|       |         |         |      |        |
  gated{19...-19...|       |         |         |      |        |
                   |       |         |         |      |        |
  -----------------+-------+---------+---------+------+--------+--------
                   |       |         |         |      |        |
  Total of 3 years |       |         |         |      |        |
                   |       |         |         |      |        |
  -----------------+-------+---------+---------+------+--------+--------
                   |       |         |         |      |        |
  Average          |       |         |         |      |        |
                   |       |         |         |      |        |
  -----------------+-------+---------+---------+------+--------+--------
                   |       |         |         |      |        |
  Per cent. of     |       |         |         |      |        |
  culturable       |       |         |         |      |        |
  commanded        |       |         |         |      |        |
                   |       |         |         |      |        |
  -----------------+-------+---------+---------+------+--------+--------

If an application refers to a whole watercourse, the Subdivisional
Officer can frequently, with the aid of an irrigation register and a set
of chak maps, both kept up to date, dispose personally of the case. A
good plan is to settle cases when on tour near the place concerned, the
applicant and the zilladar being present as well as any other persons
concerned. A certain number of cases have to come up again on the
following tour, but all are settled in less time than is occupied if the
papers go up and down between the Subdivisional Officer and the
zilladar, the “file” of papers in any particular case being constantly
swollen by reminders from the applicant.[39] Moreover, the applicants
know that their views are known to the Subdivisional Officer. If the
outlets on a channel need a general remodelling, such applications as
those under consideration receive attention in connection with the
scheme. Otherwise all the applications concerning one distributary can
be considered together. If, however, a case is pressing, or the steps to
be taken obvious, it can be settled without reference to any other case.

  [39] The plan of personal settlement is distasteful not only to the
  subordinates, but to the _munshi_ who has charge of the “vernacular
  files.” Ordinarily he can delay a case, or manipulate it to some
  extent.

The general arrangements for the “revenue” work or assessment of water
rates have been stated in Art. 1. In the Punjab the remissions for
failed crops are a source of trouble. In some districts the failed areas
are small, and no particular trouble arises, but in other districts such
areas are often very large. On perennial canals the crop inspection is
done by the zilladars, on most of the inundation canals by the
subordinates of the District Magistrate.[40] In both cases the amount of
labour involved is enormous, and the corruption to which the system
gives rise is also enormous. In the case of the inundation canals the
superior staff of the District Magistrate nominally make checks, but the
time at their disposal is wholly inadequate. In the case of the
perennial canals the Canal Engineers are able to exercise considerable
checks, but nothing like enough. In fact the state of a crop and the
proportion of the charge on it which should be remitted is a difficult
thing to judge, even if the subordinates were without guile. It is
understood that a new and statesmanlike system is now to be introduced,
the District Magistrate deciding, in consultation with the Executive
Engineer, whether the season is such as to call for any general
remission for each kind of crop, and, if so, to what extent. The
proportion to be remitted in that crop is then to be fixed, and it is to
be the same for every one.

  [40] Officially called the “Collector” in some provinces, and “Deputy
  Commissioner” in others.

It has been mentioned that some irrigation is effected by lift. The
simplest form of lift is a horizontal pole which rests, not far from its
thick end, on a support. From its thick end is suspended a bucket, and
from its thin end a weight. A man lifts the thin end so that the bucket
then dips into the water and is filled. Pulling down the thin end he
raises the bucket and empties it. A greatly improved lifting apparatus
is the Persian wheel which is vertical and has slung from it, like the
buckets of a dredger but moving vertically, a number of earthen jars,
which scoop up the water. As each jar passes over the top of the wheel
it assumes a horizontal position, discharges its water into a shoot, and
descends in an inverted position. The wheel is moved by a simple
cog-wheel arrangement actuated by a bullock which is driven round and
round in a circular track. The Persian wheel is used for lifts of any
height. The lift from a canal watercourse is a few feet, that from a
well may be 50 feet or more.

Most persons consider that a system of charging for water by volume
would be a very great advance on present methods. It has been said that
if the water were wasted it would be difficult for the cultivators to
bring home the responsibility to any individual. This objection does not
seem to have great force. Every individual would have a direct interest
in economising the water, and any cultivator who was habitually careless
would soon be detected by the others. In all probability the result
would be a great improvement in the duty of the water. But the justice
of any very rigid system of charging by volume is somewhat doubtful. The
great difference in the duty of water on different watercourses has been
mentioned more than once. Many of the causes of this are beyond the
control of the farmers, and it would probably be necessary to charge
reduced rates to some of them.




CHAPTER IV.

THE PUNJAB TRIPLE CANAL PROJECT.[41]


  [41] See Report on the Project Estimates of the Upper Jhelum, Upper
  Chenab, and Lower Bari Doab Canals.

[Illustration: FIG. 26.]


1. =General Description.= Fig. 26 shows part of the Punjab. The areas
marked L.J., L.C., U.B.D., and S.C. are already irrigated by the Lower
Jhelum, Lower Chenab, Upper Bari Doab[42] and Sirhind Canals. The areas
which it is considered very desirable to irrigate, and which are
provided for in the Triple Canal Project, are marked U.J., U.C., and
L.B.D., and the new canals are shown by dotted lines. Other areas
needing irrigation lie on the left bank of the lower part of the Sutlej,
partly in British territory and partly in Bahawalpur State, and one
area,[43] of scant rainfall and subject to occasional famine, lies
immediately South of the Sirhind Canal tract. There is also a very large
area between the Indus and the Jhelum, and it has been proposed to
irrigate it from the Indus, but on account of the presence of sand-hills
the project is not likely to be so useful as others, and it is held in
abeyance. Perhaps a small canal may be constructed, as a tentative
measure, to irrigate part of the tract.

  [42] Doab means “two waters,” or the tract between two rivers. The
  names of the three Doabs under consideration are formed from those of
  the rivers. They are called the Jech (Jhelum-Chenab), Rechna
  (Ravi-Chenab), and Bari (Beas-Ravi) Doabs.

  [43] It would be very expensive to bring water for this tract from the
  Beas and across the Sutlej.

The winter discharges of the rivers (available for the rabi crop) after
the existing irrigation has been supplied, are as follows:

  Indus,   9,434 c. feet per second (minimum)
  Jhelum,  6,800    „       „       (average)
  Chenab,   Nil
  Ravi,     Nil
  Beas,    4,000    „       „       (minimum)
  Sutlej,   Nil

In summer all the rivers have discharges (available for the kharif crop)
far exceeding any requirements. It was at one time proposed to supply
the Lower Bari Doab Canal from near the junction of the Beas and Sutlej,
and a project for this was prepared, but before it was sanctioned a
proposal was put forward to convey the surplus water of the Jhelum
eastward across the Chenab and Ravi. This valuable suggestion was made
by Sir James Wilson, who was then Settlement Commissioner of the Punjab,
and, independently, by the late Colonel S. L. Jacob, R.E., who had been
a Chief Engineer in the Punjab. The proposals were, however, to take off
the supply from the Jhelum lower down than as now arranged in the Triple
Project. This would have resulted in only a partial utilisation of the
Jhelum water, in mutilation or heavy alterations to the existing Lower
Jhelum and Lower Chenab Canals, in for ever debarring the Upper Jhelum
and Upper Chenab tracts from irrigation, and in a very costly scheme for
the Lower Bari Doab Canal.[44]

  [44] Colonel Jacob made his suggestion when in England after retiring
  from India, and when he had no levels to guide him.

The Triple Project as prepared by Sir John Benton, K.C.I.E., recently
Inspector General of Irrigation in India, gets over all the above
objections. The Upper Jhelum Canal is to irrigate the country which it
traverses, and in the winter, when the supply in the rivers is
restricted, it is to deliver into the river Chenab, above the weir at
the head of the Lower Chenab Canal, a discharge equal to that drawn out
higher up by the Upper Chenab Canal.[45] Thus the Lower Chenab Canal,
which at present draws off the whole of the water of the Chenab in
winter, will not be injuriously affected in any way. The Upper Chenab
Canal after irrigating its own tract is to deliver a large volume of
water into the Ravi. The water will be taken across that river by a
level crossing, and supply the Lower Bari Doab Canal. The water brought
into the Sutlej from the Beas will remain available for irrigation on
the left bank of the Sutlej, or possibly for the dry tract South of the
Sirhind Canal area. This fine scheme presented many difficulties and is
necessarily costly. The water has to be conveyed a great distance, and
there will be much loss by absorption. The Ravi crossing will be a very
heavy work. The Upper Jhelum Canal has to be taken by a circuitous
course round a range of hills, and to cross numerous heavy torrents. The
scheme will, however, prove remunerative in spite of immense
difficulties as to labour, caused by the outbreak of plague in the
Punjab a few years ago.

  [45] The Indus is at a higher level than the Jhelum. The latter river
  runs in a comparatively deep valley, and it is unfortunately
  impossible to convey the water of the Indus across this valley.


2. =Areas and Discharges.= The figures on which the discharges in the
Triple Project are based form a useful and interesting object lesson. In
order to obtain sufficient water in the winter, it is necessary to
reduce the rabi supply to the existing Lower Jhelum Canal. The figure
above given for the Jhelum indicates the supply available after the
reduction. More water will be supplied to the Lower Jhelum Canal for the
kharif, the canal being enlarged for this purpose, and its total
irrigation will be unaffected. The proportion of the culturable
commanded area to be irrigated in the new tracts is 75 per cent., but
from this the area irrigated by wells in the Upper Jhelum and Upper
Chenab tracts is deducted. On the Lower Bari Doab Canal there is little
well Irrigation, but there are some low-lying tracts near the rivers,
and of these only 50 per cent. will be irrigated. The kharif and rabi
areas are in all cases to be equal.

The areas to be irrigated in each crop are as below--

  Lower Jhelum Canal      383,091  acres
  Upper Jhelum Canal      172,480    „
  Upper Chenab Canal      324,184    „
  Lower Bari Doab Canal   441,264    „
                        ---------
                Total   1,321,019    „

The total, excluding the existing Lower Jhelum Canal, is 937,928 acres.
With an equal area in the other crop, the new annual irrigation amounts
to 1,875,856 acres.

The kharif duty is taken as 100 acres at the distributary heads, this
being about the figure actually obtained on the Lower Chenab and Upper
Bari Doab Canals, and the required kharif discharges at the distributary
heads are:

  Lower Jhelum                   3,821 c. feet per second
  Upper   „                      1,725    „       „
    „   Chenab                   3,242    „       „
  Lower Bari Doab                4,413    „       „
                                 -----
  Total, excluding Lower Jhelum  9,380    „       „

The losses of water in canal and branches have been found to be, on the
Upper Bari Doab Canal 10 c. feet per second, and on the Lower Chenab
Canal 8 c. feet per second, per million square feet of wetted area
respectively. The conditions of the latter canal most resemble those on
the new canals under consideration. The losses calculated on the wetted
areas of the channels, as designed, at 8 c. feet per second per million
square feet, are as follows, in c. feet per second:

  Lower Jhelum Canal      624}  1,288
  Upper Jhelum Canal      664}

  Upper Chenab Canal    1,161}  2,126
  Lower Bari Doab Canal   965}
                        -----
                 Total  3,414

But in dry years the canals will be worked in rotation during the rabi,
the Upper Chenab and Lower Bari Doab Canals being worked together, and
the Upper Jhelum and Lower Jhelum together.

When the Lower Jhelum Canal is closed, in course of rotation, the Upper
Jhelum Canal will still be flowing, and the loss in it, 664 c. feet per
second, has to be added to the figure (2,126) given above, thus bringing
up the loss to 2,790 c. feet per second.

In order to ascertain what the state of affairs will be in the rabi, the
statistics obtained on the Lower Chenab Canal were examined. These show
that the rabi duty at the distributary heads on that canal is 206 acres.
On the Upper Bari Doab Canal the duty at the distributary heads is 263
acres, but 11 per cent. of the area receives only “first waterings.” The
duty based on the remaining area is 234 acres. But the above duties are
only attained by running higher supplies in October and March than
during the intervening four months of the crop. The following remarks
and figures are taken from the Report on the Project Estimates:--

“The statistics of working of distributaries of the Chenab and Bari Doab
Canals give the average discharges shown in the following table for the
three years ending with 1903-04. The losses by absorption are calculated
on the wetted areas for the different rotational periods. The average
discharge less absorption is the supply which reached the heads of the
distributaries.

CHENAB CANAL.

  ------------------+--------------------------------------------+------
                    |                     PERIOD.                | AVER-
                    +------+------+-----+-----+-----+-----+------+ AGE.
     PARTICULARS.   | Octo-| Octo-| No- |  De-|Janu-| Feb-|March.|
                    |  ber |  ber | vem-| cem-|ary. | ru- |      |
                    | 1st- | 16th-| ber |  ber|     | ary |      |
                    | 15th |  31st|     |     |     |     |      |
  ------------------+------+------+-----+-----+-----+-----+------+------
                    |  Cu- |  Cu- | Cu- | Cu- | Cu- | Cu- |  Cu- |  Cu-
                    | secs.| secs.|secs.|secs.|secs.|secs.| secs.| secs.
  Average supply    |      |      |     |     |     |     |      |
  entering head of  |      |      |     |     |     |     |      |
  canal             |10,196|10,285|7,788|5,593|5,127|5,500| 6,603| 6,809
                    |      |      |     |     |     |     |      |
  Deduct absorption | 1,633| 1,633|1,250|1,053|1,032|1,171| 1,433| 1,262
                    +------+------+-----+-----+-----+-----+------+------
  Supply at distrib-|      |      |     |     |     |     |      |
  utary heads for   |      |      |     |     |     |     |      |
  1,155,685 acres,  |      |      |     |     |     |     |      |
  the average Bari  |      |      |     |     |     |     |      |
  area              | 8,563| 8,652|6,538|4,510|4,095|4,329| 5,170| 5,546
                    +------+------+-----+-----+-----+-----+------+------
  Proportional      |      |      |     |     |     |     |      |
  supply for        |      |      |     |     |     |     |      |
  1,164,595 acres   | 8,631| 8,721|6,590|4,576|4,128|4,364| 5,211| 5,591
                    |      |      |     |     |     |     |      |
  Add absorption for|      |      |     |     |     |     |      |
  new projects      | 3,414| 3,414|2,139|2,139|2,139|2,139| 3,414| 2,564
                    +------+------+-----+-----+-----+-----+------+------
  Supply required   |      |      |     |     |     |     |      |
  for new projects  |      |      |     |     |     |     |      |
  at heads of canals|12,045|12,035|8,729|6,715|6,267|6,503| 8,625| 8,155
  ------------------+------+------+-----+-----+-----+-----+------+------

“The average discharge given by the third line is 5,546, and the average
area being 1,155,685 acres, the duty at the heads of distributaries was
208.

“The area 1,164,595 is the perennial rabi irrigation of the new
projects, the area 156,424 acres, receiving only first waterings, being
omitted to admit of a fair comparison, and is only 1 per cent. under the
average attained on the Chenab Canal in the three years for which the
table is prepared.

“The absorption added for the two first periods is on the supposition
that all the canals are open throughout October and March, tatilling[46]
with an average absorption loss of 2,139 cusecs[47] being in force
during the other four months. The last line of the table shows the
average Rabi discharge required by the new projects at the heads of
canals, inclusive of all losses calculated on the Chenab Canal basis of
a duty of 208 acres per cusec obtained at the heads of distributaries.

  [46] “Tátíl” is the Indian word for rotational closure.

  [47] “Cusec” is used in India for c. ft. per second.

“The Bari Doab Canal statistics furnish the means of the adequacy of
available supply being gauged. The following table furnishes particulars
for the average supply of water entering the head of the canal for the
five years 1898-99, 1899-1900, 1901-02, 1902-03, 1903-04. The figures
for the year 1900-01 are omitted, as it was a very abnormal one of very
plenteous supply and heavy rainfall:--

“The average irrigation for the five years in question was 442,302
inclusive of 11 per cent. which only receives first waterings. This
divided by the average supply, 1,685, entering the head of a canal gives
a duty of 263 acres per cusec at the heads of distributaries.

BARI DOAB CANAL.

  ------------------+--------------------------------------------+------
                    |                     PERIOD.                | AVER-
                    +------+------+-----+-----+-----+-----+------+ AGE.
     PARTICULARS.   | Octo-| Octo-| No- |  De-|Janu-| Feb-|March.|
                    |  ber |  ber | vem-| cem-|ary. | ru- |      |
                    | 1st- | 16th-| ber |  ber|     | ary |      |
                    | 15th |  31st|     |     |     |     |      |
  ------------------+------+------+-----+-----+-----+-----+------+------
                    |  Cu- |  Cu- | Cu- | Cu- | Cu- | Cu- |  Cu- |  Cu-
                    | secs.| secs.|secs.|secs.|secs.|secs.| secs.| secs.
  Average supply    |      |      |     |     |     |     |      |
  entering head of  |      |      |     |     |     |     |      |
  canal             | 3,769| 2,896|2,170|1,755|1,622|1,916| 2,909| 2,284
                    |      |      |     |     |     |     |      |
  Deduct absorption |   599|   599|  599|  599|  599|  599|   599|   599
  ------------------+------+------+-----+-----+-----+-----+------+------
  Supply at heads of|      |      |     |     |     |     |      |
  distributaries    |      |      |     |     |     |     |      |
  (_a_)             | 3,170| 2,297|1,571|1,156|1,023|1,317| 2,310| 1,685
  ------------------+------+------+-----+-----+-----+-----+------+------
  Corresponding     |      |      |     |     |     |     |      |
  supply for new    |      |      |     |     |     |     |      |
  schemes 3 ×       |      |      |     |     |     |     |      |
  figures line (_a_)| 9,510| 6,891|4,713|3,468|3,069|3,951| 6,930| 5,055
                    |      |      |     |     |     |     |      |
  Add absorption for|      |      |     |     |     |     |      |
  new projects      | 3,414| 3,414|2,139|2,139|2,139|2,139| 3,414| 2,564
  ------------------+------+------+-----+-----+-----+-----+------+------
  Supply required   |      |      |     |     |     |     |      |
  for new projects  |      |      |     |     |     |     |      |
  at heads of canals|12,924|10,305|6,852|5,607|5,208|6,090|10,344| 7,619
  ------------------+------+------+-----+-----+-----+-----+------+------

“The rabi irrigation of the new projects is 1,321,019 acres,[48] and
this divided by 442,302 gives approximately the multiplier 3 referred to
at (_a_) in the above table.

  [48] Including the Lower Jhelum.

“The figures given in the above table and in the foregoing remarks
relate to the aggregate of the areas in the rabi which receives a
perennial supply and which only receives first and last waterings. On
the Upper Bari Doab Canal the rabi which receives perennial irrigation
is averagely 393,649 acres; the average supply of 1,685 cusecs gives on
this area a duty of 234 acres per cusec at the heads of the
distributaries.

“In the case of the three projects the aggregate _rabi_ area receiving
perennial irrigation as shown by the table, paragraph 21[49] _supra_, is
1,164,595 acres: this is 2·96 times 393,649; so that the proportional
supply required on this basis would be slightly less than that given by
the multiplier 3 in the above table.

  [49] Not printed. The area is the total rabi area less the area which
  is to receive only first waterings.

In explanation of the difference of the duties:--

  Lower Chenab Canal     208 acres per cusec,
  Upper Bari Doab Canal  234 ditto,

it may be stated that the Lower Chenab Canal is a comparatively new
work, and that the duty has been steadily rising and, with the perfect
watercourse system, may be relied on to reach the Upper Bari Doab Canal
234 acres per cusec in the course of time for water arriving at the
heads of distributaries.

       *       *       *       *       *

“27. =Summary of conclusions as to sufficiency of supply.=--The
following table shows all the foregoing results in a form readily
admitting of comparison:--

  ----------+----------------------------------------------------------+
  PARTIC-   |                          PERIOD.                         |
  ULARS.    +---------+--------+-------+-----+------+---------+--------+
            | 1st to  | 6th to | Novem-| De- | Janu-|  Febru- | March. |
            |  15th   |  31st  |  ber. | cem-|  ary.|   ary.  |        |
            | October.|October.|       | ber.|      |         |        |
            |         |        |       |     |      |         |        |
  ----------+---------+--------+-------+-----+------+---------+--------+
            | Cusecs. | Cusecs.|Cusecs.| Cu- |  Cu- | Cusecs. | Cusecs.|
            |         |        |       |secs.| secs.|         |        |
  AVERAGE   |         |        |       |     |      |         |        |
  SUPPLIES  |         |        |       |     |      |         |        |
  AVAILABLE.|         |        |       |     |      |         |        |
            |         |        |       |     |      |         |        |
  Very fa-  |         |        |       |     |      |         |        |
  vourable  |{ 21,400 | 15,150 |}11,850|8,626|11,200|{ 13,100 | 21,250 |
  years 1   |{(13.063)|(13,063)|}      |     |      |{(13,063)|(13,063)|
  in 4      |         |        |       |     |      |         |        |
            |         |        |       |     |      |         |        |
  Ordinary  |{ 13,900}| 11,850 | 10,000|7,400| 7,600|   9,100 |{16,500 |
  years 2   |{ 13,063}|        |       |     |      |         |{13,063 |
  in 4      |         |        |       |     |      |         |        |
            |         |        |       |     |      |         |        |
  Dry years |  10,150 |  9,100 | 7,275 |5,950| 5,610|   6,100 | 11,345 |
  1 in 4    |         |        |       |     |      |         |        |
            |         |        |       |     |      |         |        |
  Minimum of|   9,710 |  8,003 | 6,624 |5,810| 5,563|   5,163 |  9,791 |
  14 years  |         |        |       |     |      |         |        |
            +---------+--------+-------+-----+------+---------+--------+
  Require-  |         |        |       |     |      |         |        |
  ments on  |         |        |       |     |      |         |        |
  average of|         |        |       |     |      |         |        |
  Lower     |  12,045 | 12,135 | 8,729 |6,715| 6,267|   6,503 |  8,625 |
  Chenab    |         |        |       |     |      |         |        |
  Canal for |         |        |       |     |      |         |        |
  3 years   |         |        |       |     |      |         |        |
            |         |        |       |     |      |         |        |
  Require-  |         |        |       |     |      |         |        |
  ments on  |         |        |       |     |      |         |        |
  average of|         |        |       |     |      |         |        |
  Upper Bari|  12,924 | 10,305 | 6,852 |5,607| 5,208|   6,090 | 10,344 |
  Doab Canal|         |        |       |     |      |         |        |
  for 5     |         |        |       |     |      |         |        |
  years     |         |        |       |     |      |         |        |
  ----------+---------+--------+-------+-----+------+---------+--------+

  ----------+-------+-------+---------+-----------+-----------
  PARTIC-   |Average|Deduct |Supply at|Duty calcu-|Duty calcu-
  ULARS.    +supply |loss by|heads of | lated on  | lated on
            |  in   |absorp-|distribu-|1,321,019  |1,164,595
            | river.| tion. | taries. |acres, the |acres, the
            |       |       |         |gross rabi | perennial
            |       |       |         |   area.   |  area.
  ----------+-------+-------+---------+-----------+-----------
            |Cusecs.|Cusecs.| Cusecs. |           |
            |       |       |         |           |
  AVERAGE   |       |       |         |           |
  SUPPLIES  |       |       |         |           |
  AVAILABLE.|       |       |         |           |
            |       |       |         |           |
  Very fa-  |       |       |         |           |
  vourable  |}11,811| 3,414 |  8,397  |     158   |     139
  years 1   |}      |       |         |           |
  in 4      |       |       |         |           |
            |       |       |         |           |
  Ordinary  |} 9,946| 2,989 |  6,957  |     189   |     167
  years 2   |}      |       |         |           |
  in 4      |       |       |         |           |
            |       |       |         |           |
  Dry years |  7,651| 2,564 |  5,087  |     259   |     229
  1 in 4    |       |       |         |           |
            |       |       |         |           |
  Minimum of|  6,968| 2,458 |  4,510  |     293   |     258
  14 years  |       |       |         |           |
            +-------+-------+---------+-----------+-----------
  Require-  |       |       |         |           |
  ments on  |       |       |         |           |
  average of|       |       |         |           |
  Lower     |  8,155| 2,564 |  5,591  |     236   |     208
  Chenab    |       |       |         |           |
  Canal for |       |       |         |           |
  3 years   |       |       |         |           |
            |       |       |         |           |
  Require-  |       |       |         |           |
  ments on  |       |       |         |           |
  average of|       |       |         |           |
  Upper Bari|  7,619| 2,564 |  5,055  |     261   |     230
  Doab Canal|       |       |         |           |
  for 5     |       |       |         |           |
  years     |       |       |         |           |
  ----------+-------+-------+---------+-----------+-----------

“The 13,063 shown in brackets represents the parts of the available
supply which the canals can carry, the capacity being as follows:--

                      Cusecs.
  Lower Jhelum Canal   4,563
  Upper Jhelum Canal   8,500
                      ------
               Total  13,063
                      ------

“The average supplies and duty figures are based on the 13,063 cusec
maximum capacity and not on the larger available supplies written above
these figures where they occur.

“The above table goes to show the following:

  (_i_) In order to utilize the large supplies available in the Jhelum
  River in October and March every year and in some or all of the
  intervening months in other years, it is advisable to give the Upper
  Jhelum Canal the large capacity of 8,500 cusecs proposed.

  (_ii_) In favourable and ordinary years, that is, in 3 out of 4, the
  available supply will be ample, as shown by the low duties of 189 and
  167 compared with those obtaining on the Lower Chenab and Upper Bari
  Doab Canals.

  (_iii_) In dry years, that is, 1 in 4, it will be necessary to attain
  a duty almost exactly the same as that now obtaining on the Upper Bari
  Doab Canal.

  (_iv_) That an exceptionally dry year might occur once in 14 years,
  when the supply would be 10 per cent. short of that required by the
  average Upper Bari Doab Canal standard of requirements: such
  exceptional cases should be met by remissions, which will be far
  preferable to wasting the good supplies of 13 years out of 14.

  (_v_) That the occasional occurrence of dry years makes it inadvisable
  to attempt a greater proportion of rabi than half of the annual
  irrigation.”


3. =Remarks.= The Report on the Project estimates gives, for each tract,
remarks on its soil, rainfall, height of subsoil water, circumstances as
to existing irrigation from wells or small canals and liability to
floods. On a consideration of these matters the decision as to the
particular parts of the tracts which are to be irrigated and the areas
which are, in the rabi, to receive only restricted irrigation,
depends.[50]

  [50] It is not unusual, in tracts where the level of the subsoil water
  is high, say within 15 feet of the surface, to have some “kharif
  distributaries.” These are closed in the rabi. This tends to prevent
  water-logging of the soil. In the rabi the people lift water from
  wells. There may also be kharif distributaries in dry tracts if there
  is no water to spare in the rabi.

In calculating the sizes of the canals, N in Kutter’s co-efficient was
taken at ·020. In sharp curves the bed is paved on the side next the
concave bank. In high embankments where the soil is sandy the best
material is used as a core wall. The torrent works on the Upper Jhelum
Canal have been mentioned in _River and Canal Engineering_, Chapter XII.

Regarding the effect of the new canals on the inundation canals which
take off, lower down, from the Chenab below its confluence with the
Jhelum, it has for long been the policy to gradually shift the heads of
these canals upstream in order to obtain better supplies, or rather to
counteract the effect of the abstraction of water for the recently
constructed Lower Chenab and Lower Jhelum Canals. Any such abstraction
of water has not much effect on the floods, but it has much effect in
April and May, when the rivers have not fully risen, and in September,
when they are falling.

In order to estimate the effect on the water level of the Chenab--below
its junction with the Jhelum--it was necessary to observe discharges of
the river, not only in the winter when it is low, but in the summer when
it is high. The depth of the water was in some places 40 feet, and the
stream 2,000 feet wide. Fortunately the Subdivisional Officer was a
native of India and did not much mind the sun. A discharge curve (_River
and Canal Engineering_, Chapter III. Art. 5,) having been prepared, it
was possible to construct a diagram with periods of time as the
abscissas, the ordinates representing the average known gauge readings
on the different dates and another set of ordinates representing the
probable discharges. By deducting the discharges which it was intended
that the new perennial canals should draw off, it was possible to draw
fresh ordinates representing the diminished river discharges and the
reduced river gauge readings corresponding to them. It was found that
the water level would be lowered by about 1·3 feet in April and May, and
by about 1·5 feet in September. It was, however, shown that by shifting
the heads of the inundation canals upstream--the gradients of the canals
being flatter than that of the river--the effect of the lowering of the
water level could, as heretofore, be nullified.




CHAPTER V.

PROPOSED IMPROVEMENTS IN IRRIGATION CANALS.


1. =Preliminary Remarks.=--The chief improvements which have been under
consideration during recent years are three in number. The first is
increased economy of water in its actual use in the fields; the second
is reduction of the losses by absorption in the channels; and the third
is distribution by means of modules.

Regarding the first, it has long been known that the ordinary methods of
laying on the water are more or less wasteful. In California, when the
water instead of being applied to the surface of the ground, is brought
in a pipe and delivered below the ground level, the duty is increased
from 250 to 500 acres. In India a field is divided, by means of small
ridges of earth, into large compartments. The water is let into a
compartment and gradually covers it. By the time the further side is
soaked the nearer side has received far too much water. Frequently the
water for a compartment, instead of being carried up to it by a small
watercourse, is passed through another compartment and this adds to the
waste. Also the number of waterings given to a crop is often 5 or 6,
when 4 would suffice. Experiments made on the Upper Bari Doab Canal, by
Kennedy, showed that the water used in the fields was nearly double what
it might have been. The 53 c. ft. shown in Chapter 1, Art. 4, as
reaching the fields, were used up when 28 c. ft. would have sufficed. It
is not certain that the waste is generally quite as much as the above.
It is possible that the restricted supplies might have given smaller
yields of crops. More recent experiments made by Kanthack on the same
canal give the needless waste as about 25 per cent. The field
compartments ought, according to Kennedy, to be 70ft. square, the small
branch watercourses being 140ft. apart. It would be better to have still
smaller compartments, but this would be rather hard on the people.

At one time Government issued orders, in Northern India, that
compartments of 1296 square feet were to be used, and that, otherwise,
increased water rates would be charged, but the orders were never
enforced. They were thought to press too hardly on the people. Extreme
measures for enforcing economy in the use of water in any country are
likely to be introduced only when they become absolutely necessary owing
to the supplies of water being otherwise insufficient.


2. =Reduction of Losses in the Channels.=--For several years experiments
have been going on in the Punjab as to the effect of lining watercourses
with various materials. The following conclusions have been arrived
at[51]:--

  [51] _Punjab Irrigation Paper_ No. 11 C. “Lining of Watercourses to
  reduce absorption losses. Experiments of 1908-1911.”


I. ORDINARY UNLINED TRENCHES.

  (_a_) The rate of absorption varies greatly, and this is due probably
  to unequal fissuring of the upper layers of the soil.

  (_b_) The rate of absorption in the three hottest months averaged
  ·0571 feet per hour, or more than double the rate (·026) in the three
  coldest months. The difference is ascribed to the greater viscosity
  of the water when cold.

  (_c_) The average losses with canal water were ·0315 feet per hour, or
  8·75 c. feet per second per million sq. feet.[52] With well water the
  figures were ·1096 and 30·5. The conclusion is that the silt in canal
  water reduces the losses by more than two-thirds.

  [52] This loss of 8·75 c. ft. per second was in water only about a
  foot deep. This confirms the conclusion arrived at in Chapter I, Art.
  4, that the depth of water is not a factor of much importance.

  (_d_) With canal water the average loss decreased by 40 per cent.
  (from ·0491 to ·0293) in about four years. This was no doubt due to
  the effect of the silt. With well water the loss at the end of four
  years (·2293) was nearly four times as great as at first (·0591). This
  may have been due to removal of the finer particles of soil by the
  water, but the experiments were made at only one place, and were not
  conclusive.


II. LINED TRENCHES.

  (_e_) With trenches lined with crude oil ¹⁄₁₆ inch thick, or with
  Portland cement ¹⁄₁₆ inch thick, or with clay puddle 6 inches thick,
  the “efficiency ratios,” as compared with unlined trenches, are
  respectively about 4·0, 5·7 and 5·7, the age of the lining being four
  years. The efficiency ratio is the inverse of the loss. Thus with an
  efficiency ratio of 3 the loss in the lined trench is 33 per cent. of
  that in the unlined trench.

  (_f_) The efficiency ratio in the case of oil may diminish at the rate
  of 10 per cent. per annum, but in the case of cement and clay puddle
  it tends to increase rather than to decrease.

Assuming that the efficiency ratios are only 3·0, 4·5 and 4·5, and that
the loss in an unlined channel is 8 c. feet per second per million sq.
feet, the saving in water by using channels lined with oil, cement and
puddle respectively would be 5·33, 6·25 and 6·25 c. feet per second. The
average duty of the water at the canal head is about 242 acres, and the
average revenue per acre is Rs 3·93. The revenue from 1 c. ft. of water
at the canal head is thus Rs 950. Only about half the water reaches the
fields (Chapter I., Art. 4), and the revenue from 1 c. ft. of water
which reaches the fields is about Rs 1900. The mean of the above two
sums is Rs 1425. If 6 c. ft. of water per second could be saved the
revenue would be increased by Rs 8,550 per annum.

The cost of lining a million square feet of channel with oil, cement and
puddle is estimated at Rs 30,000, Rs 27,500 and Rs 35,000 respectively.
Allowance has to be made for the fact that watercourses flow
intermittently, and that a lined channel gives no saving when it is not
in flow, also that extensions of canals might have to be undertaken in
order to utilise the water saved. After making these allowances it is
estimated, in the paper above quoted, that the saving effected by lining
a million square feet with oil, cement or puddle represents the interest
on a capital sum of Rs 69,300, Rs 81,250 and Rs 81,250 respectively, or
2 or 3 times the sums sunk in constructing the linings.

Hitherto the experiments have been carried out on a moderate scale, but
extensive operations are now being undertaken on the Lower Chenab
Canal, and possibly on others.

In cases where it is not desired to incur much expenditure, it may be a
good plan to construct watercourses to a cross section somewhat larger
than that ultimately desired. The silt deposited on the bed and sides
forms, in most cases, a more impervious lining than the original soil.
The same plan can be adopted in the tail portion of a distributary. In a
larger channel there would be less certainty that any deposit would take
place unless short lengths, at frequent intervals, were excavated to the
true or ultimate section, so as to form weirs and spurs; and even these
might not stand.

In Italy, in cases where the water naturally contains lime in
suspension, the beds of canals have become gradually watertight by the
deposit of lime in the channel.[53] In some cases lime has been
artificially added. It appears that a considerable period of time is
necessary for the process.

  [53] Min. Proc. Inst. C. E. Vol. CXVI.


3. =Modules.=--A module is an appliance which automatically gives a
constant discharge through an aperture, however the water level on
either the upstream or downstream side of the aperture may fluctuate. In
an old and simple form of module there is a horizontal orifice in which
works loosely a tapering rod attached to a float. The water passes
through the annular space surrounding the rod. If the water level rises,
the rise of the float brings a thicker part of the rod to the orifice
and reduces the annular space. In another kind of module the water is
discharged through a syphon. If the water level alters, the syphon moves
in such a way that the head, or difference between the levels of its
two ends, remains the same. The great objections to modules are that
they are liable to get out of order or to be tampered with. A module
recently invented and patented by Gibb[54] has no movable parts, and is
not liable to these objections.

  [54] For description see Appendix H.

A few years ago the question of the desirability of using modules for
the outlets of distributaries in India was raised. The opinions of a
large number of the senior canal engineers were called for and
considered, and since then the subject has been thoroughly discussed.
There are certain inherent difficulties in the way of moduling the
outlets of a distributary. Owing, for instance, to rain further up the
canal, or to the closure of a distributary owing to a breach in it, the
canal supply may increase, and it may be necessary to let more water
into the distributary under consideration. Under the present system any
excesses of water are automatically taken by the outlets. If all outlets
were rigidly moduled they would discharge no more than before the excess
supply came in, and the excess supply would all go to the tail of the
distributary, and, most likely, breach the banks. To get over this
difficulty, the module has to be so arranged that when the water level
in the distributary rises to a certain “maximum limit” the module ceases
to act as such, and the discharge drawn off from the distributary
increases as the water level rises. Again, the discharge of the
distributary may at times be considerably less than its full supply. In
order that, in such a case, the outlets towards the tail of the
distributary may not be wholly deprived of water, it has to be arranged
so that when the water level in the distributary falls below a certain
“minimum limit” the modules cease to act as such, and draw off supplies
which are less the lower the water level. Such supplies are not in
proportion to the full supplies of the outlets. It will, however, be
shown presently that low supplies need seldom be run. When a
distributary, say the upper reach, contains silt, the water level
corresponding to a given discharge is higher than before, and care has
to be taken that the maximum limit is high enough. At the same time the
minimum limit must be so low that it will not be passed when the silt
scours out. The difference between the maximum and minimum limits is
called the “range” of the module.

In Gibb’s module the above conditions can be complied with. The module
is placed outside the bank of the distributary. The water is drawn off
from the distributary by a pipe, whose lower edge is at the bed level of
the distributary, and delivered from the module into the watercourse
through a rectangular aperture at a higher level than that of the pipe.
It is possible that, owing to the high level of the aperture, some
rolling silt which would otherwise have passed out of the distributary
may remain in it. The height of the aperture also prevents the
watercourse from drawing off any water at all when the water level of
the distributary falls below a certain level, but this objection is not
important. An escape weir or notch is provided so that when the water
level in the distributary rises to the maximum limit some water
overflows into the watercourse. On the whole it appears that all
difficulties can be got over, though a good deal of care and precision
is necessary in fixing the exact height of the maximum and minimum
limits.

The difficulties under consideration will all be reduced if some of the
outlets on a distributary are left unmoduled, and this is desirable on
other grounds. When the supply is normal, _i.e._ between the maximum and
minimum limits, and all modules are working, the supply entering the
distributary must be regulated with great precision. The outlets draw
off a certain supply. If less than this enters the distributary the tail
outlets must go short. If more enters there will be a surplus at the
tail, though it can probably be disposed of, because the tail water will
rise above the maximum limit. For short periods, say an hour or two, no
trouble arises because the distributary acts as a reservoir, the water
level rising to take in any excess supply, and falling to allow for a
deficiency. At the tail the rise and fall may be hardly perceptible. But
if the supply were deficient for a whole night the tail outlets would
certainly go short. This could theoretically be remedied to some extent
by letting in an excess supply for a short time and causing the water
level at the tail to rise above the maximum limit, but in practice no
such system of compensation could be worked. The very fact of the tail
outlets having gone short for a night would not be known. The proper
method of preventing any such troubles as those under consideration is
to leave some of the outlets on the distributary un-moduled.

It has been more than once mentioned that there are periods when a
distributary is run, not full, but about three-fourths full. If that
were done in the case of a distributary whose outlets were mostly
moduled, the water level would probably be below the minimum limit, and
the modules would not be acting as such. The outlets would not, under
these circumstances, obtain their proper proportionate supplies. This
difficulty can, no doubt, be got over by running the distributary full
for short periods at a time instead of three-fourths full for longer
periods. The people, when once they understood the case, could arrange
to use the water in greater volume for two days instead of in smaller
volume for three. If this arrangement comes into force it will not be
necessary to design distributaries--see Chapter III, Art. 4--so as to
have a good command when three-fourths full supply is run.

On nearly every distributary there are some watercourses whose command
is bad, and it has been stated (Chapter II, Art. 9) that in an ordinary
unmoduled distributary the sizes of the outlets in such cases should be
extremely liberal. To module any such outlet would cause a lowering of
the water level in the watercourse and would interfere with the
irrigation. Such outlets should not be moduled. Again, there are some
few outlets which are not submerged, _i.e._, there is a free fall into
the watercourse. The discharge does not depend on the water level in the
watercourse, and it is not affected by any enlargement or clearance of
it. It depends only on the water level in the distributary. This water
level, if most of the outlets are moduled, will be fairly constant. Such
outlets need not be moduled, and they should not be moduled unless the
other unmoduled outlets in the reach concerned are sufficiently
numerous, and perhaps not even then, because moduling involves some
expense.

A distributary generally has some falls which divide it into reaches.
Immediately upstream of a fall the water level for a given discharge is
not affected by the silting or scouring of the channel. Any outlets near
to and upstream of the fall are less subject than others to variation in
discharge, and are suitable for non-moduling in case a sufficient number
of unmoduled outlets is not otherwise obtainable.

Regarding the watercourses at the extreme tail of a distributary it has
been pointed out (Chapter III., Art. 7) that in an ordinary case they
should not be left without masonry outlets, because they may then lower
the water level and so unfairly reduce the supply of any watercourse,
even though upstream of them, which has such an outlet. But any outlets
near the tail of a distributary can suitably be left unmoduled because
of the difficulty of ensuring that the supply at the tail shall be
exactly what is needed.

Gibb’s modules have been tried on various distributaries in the Punjab
and found to give good results. It is believed however that in only one
case has a whole distributary been moduled. The distributary is a large
one, its length being 35 miles. It appears that the discharge reaching
the tail of the distributary is not constant but varies, as was to be
expected, when the head discharge varies for any length of time. The
command on the distributary is good. There is nothing to show that
matters would not have been improved, and money saved, by leaving some
of the outlets without modules.

It has been remarked above, that at the downstream end of a reach ending
in a fall, the F.S. level of a distributary is not affected by silt. At
the upstream end of the reach it is affected. There are thus two
gradients, one flat, and one steep. It appears to have been decided in
one case in the Punjab, that the minimum limit of supply for the module
should be about half an inch below the flat line and the maximum limit
·3 feet above the steep line. In many cases a greater range would be
required,[55] say a foot.

  [55] It is understood that a range of a foot can easily be arranged
  for, and that ranges of 3 or 4 feet can be introduced at slightly
  increased cost.

In Chapter III. Art. 7, the case of a distributary without modules but
with the outlets carefully adjusted, was considered. The question to be
decided in each case is whether such an arrangement is preferable to
moduling some of the outlets. This turns largely on the amount of
attention which would be bestowed on the case. In view of the difficulty
of securing such attention and of the trouble of constantly making
alterations in a certain number of outlets, it is probable that moduling
will in many cases be considered preferable.

The question of moduling the heads of distributaries has also been
considered in the Punjab. For minor or small distributaries modules are
feasible. For a large distributary a module would be expensive and it
appears that the present system of regulating is preferable.

Kennedy’s “Gauge Outlet,” which is a kind of semi-module is described in
Appendix K. It is being tried in the Punjab.




APPENDICES.


APPENDIX A.

DIVIDE WALL ON LOWER CHENAB CANAL.

(See page 50, first footnote.)

[Illustration: FIG. 27.]

The Gagera branch of the Lower Chenab Canal--the left-hand branch in
fig. 27--was found to silt. It was proposed to make a divide wall (fig.
27) extending up to full supply level. The idea is unintelligible. The
silt does not travel by itself but is carried or rolled by the water. As
long as water entered the Gagera branch, silt would go with it. The
authorities, who had apparently accepted the proposal, altered the
estimate when they received it, and ordered the wall to be made as shown
dotted and of only half the height. This was done. The idea seems to
have been that the wall would act as a sill and stop rolling silt. This
is intelligible, but such sills do not always have much effect on
rolling silt. Moreover, there was a large gap, A B, in the wall. The
work is said to have proved useless, and proposals have been made to
continue the wall from A to B. In this form it is conceivable that it
may be of use.


APPENDIX B.

SPECIFICATION FOR MAINTENANCE OF CHANNELS.

(See page 138.)


I. ROADS AND BANKS.


1. =Filling Holes.=--Holes to be all dug out and thoroughly opened and
inspected, then to be filled in with rammed earth. Never to be filled in
a hurry or without digging out.


2. =Dressing.=--Heavy soil to be dressed even. Light sandy soil to be
disturbed as little as possible, and grass in such soil not to be
removed except when in large tufts. When dressing is done, the road to
be given (as far as possible) a transverse slope from the canal side of
about 1 in 50.


3. =Trees.=--Branches to be lopped so as not to obstruct riders. Great
care is needed to see that the men do not lop needlessly high. Roots, if
projecting on road, to be covered up or cut out.


4. =Petty Repairs.=--Settlement or wearing down, if slight, should be
made good on maintenance estimates, otherwise on special estimates.
Cracks should be dug out and filled in and rammed. Old “dead men” or
walls of earth should be utilised or at least levelled down.


5. =Sand or “Reh” Soil.=--Can be dug out to a depth of 9 inches and
removed to a distance, and (the places having been inspected by the
Subdivisional Officer) replaced by good soil got from pits or berms, the
places being selected with care. If the lead is slightly askew, the
stuff removed can be put in the same pits from which earth is got.


6. =Laying long coarse Grass on Road.=--This can be done in cases where
the removal of sand or “reh” is not practicable or has proved
ineffective. The grass is laid crosswise to prevent wheels sinking in.


II. JUNGLE AND TREES.


1. =Jungle.=--To be cut close to the ground or to be dug out by the
roots when ordered. To be burned as soon as dry. Dead branches, twigs,
etc., to be burned or removed to rest-houses, and not left about on
canal land. Precautions to be taken against damage by fire to forests,
etc. Clearance to include the channel[56] and both roads, and any jungle
on the slopes of the spoil which obstructs the roads.[57]

  [56] Jungle on inside slopes not to be cleared where banks fall in or
  where channel is too wide.

  [57] When an embankment runs parallel to an inundation canal, a chain
  or so distant, the intervening space need not be cleared, nor need the
  top of a bank be cleared if it is so uneven that it is not a road.


2. =Trees.=--Trees which fall into a channel or across a road to have
their branches cut away at once. The trunk to be removed so far as is
possible. Trees which are dead or broken off should be felled, also
those which have been blown into inclined positions, unless bad gaps
will be caused. Trees (unless required for stock) to be sold as they lie
and removed, including the parts below ground, by purchasers, within a
fixed time. Logs, etc., not to be left lying about on canal land.
Stumps, etc., to be made into charcoal and the holes filled up.

_Note._--The above works (Parts I. and II.) to be done immediately after
the rains (repairs to roads and removal of trees, branches, etc., being
also done during the rains or whenever necessary) and finished at latest
by 31st October.


III. CATTLE CROSSINGS OR GHÁTS.


1. =Repairs.=--Gháts to be dressed, strengthened, and kept neat, the
bank being thrown back and curved so as to give a long inner slope, and
lumps, etc., levelled off.


2. =Closures.=--To be closed (by order of Subdivisional Officer and no
one of lower rank) only when very near to a bridge or near to another
ghát.[58] If closed, to be staked up and bushing to be added. Not to be
closed by loose thorny branches. Not to be allowed close to any
milestone, outlet, etc.

  [58] Regarding gháts at bridges, see Chap. II., Art. 12.


3. =Small Gháts.=--Gháts where only foot-passengers cross, can run
diagonally up the slopes or as may be convenient. They should be dressed
and kept in order.


4. =Canal Road at Gháts.=--At all gháts care must be taken that the
canal road, especially if used for driving, is not cut up and is kept in
proper order.


IV. MISCELLANEOUS ITEMS.


1. =Rubbish or Obstructions in Bed of Channel.=--To be removed from the
channel when it is laid dry, and not left till it is about to be
reopened.[59] Old stakes, etc., to be sawn off when crooked or too high.

  [59] Where the bed is too low, no rubbish clearance should be done
  except in the case of very large snags, etc.


2. =Temporary Aqueducts or Damaged Wooden Bridges.=[60]--To be removed
before water is expected (but not sooner than is necessary) and the
banks repaired and made good.

  [60] This applies to inundation canals.


APPENDIX C.

SPECIFICATION FOR MAINTENANCE OF MASONRY WORKS.

(See page 138.)


1. =General Repairs.=--Masonry, plaster, pitching, etc., to be kept in
repair. Pitching, where defective or out of line, to be made right.
Bumping posts to be fixed in proper positions. Earth to be added to
ramps, etc., where needed. Metalling to be regularly seen to. Needles,
planks, hooks, railings, winches, lamp-posts, lamps, etc., to be kept in
order and complete. Bricks, bats, etc., to be properly stacked. Needles,
etc., to be neatly stacked on rests or with bricks under them. All
surplus and useless needles, etc., to be removed. Huts to be kept in
repair. Extra mud walls or screens not to be allowed when unsightly. All
verandah openings to be edged with a 6-inch band of whitewash.


2. =Jungle.=--All masonry to be kept free from jungle growth, and all
piers free from caught jungle. For this purpose long bamboo weed-hooks
to be supplied.


3. =Dressing, etc.=--Rubbish, lumps of earth, logs, etc., to be cleared
away, pits and holes filled up. Banks, slopes, etc., of main and branch
channels in the neighbourhood of the work to be specially levelled and
dressed.

_Note._--All works should be specially seen to in October, and
everything be in order by 31st October.


APPENDIX D.

WATCHING AND PROTECTING BANKS AND EMBANKMENTS.[61]

(See page 138.)

  [61] This is reprinted from _Punjab Rivers and Works_. It was drawn up
  for inundation canals and flood embankments.


1. =Watching.=--Every watchman employed to have a fixed headquarters and
a fixed beat. If there is no permanent hut on or near the bank, grass
huts should be erected by the men at the places fixed. The presence or
absence of the men to be frequently tested by the mate and suboverseer.
The suboverseers tests to be recorded in a book and to form the subject
of frequent inquiry by the Subdivisional Officer, who will also record
his remarks and take proper action in case the suboverseer is in fault.


2. =Gauge Readers, Regulating Establishment, Bungalow Watchmen,
etc.=--To be made to assist whenever possible. The allotment of a beat
to each such man has been separately ordered.


3. =Employment of Men on Repairs.=--The men, when not otherwise
occupied, to do petty repairs, etc., within their beats, but not to be
put on miscellaneous duties and sent about as messengers, nor to act as
orderlies or khalassies.


4. =Strength of Establishment.=--Should generally be greater for one
and a half months in July and August than at other times. Care to be
taken as to this and as to dismissing men when no longer needed.


5. =Stakes and Mallets.=--To be collected beforehand, if necessary, at
suitable places, to be accounted for at end of flow season and balance
taken care of.


6. =Breaches.=--The Establishment to be trained by the Subdivisional
Officer to report every breach to all officials with the greatest
possible speed. The mate, daroga, and suboverseer to remain there till
the breach is closed and to promptly send a report on the prescribed
form to the Subdivisional Officer.


7. =Serious Breaches.=--In case of serious breaches of main channels the
Subdivisional Officer to himself reach the spot as soon as possible.


8. =Breach Reports.=--See printed form M[62] attached. To be promptly
submitted for each breach to the Executive Engineer. The report contains
a column for cost of closure. This means the stoppage of the flow and
not the complete making up of the banks. The column for remarks of the
Executive Engineer should be filled in and the report promptly returned
to the Subdivisional Officer, who will, in the meantime, be making up
the banks and preparing a requisition or estimate.

  [62] Not printed.


9. =Progress Report.=--With the Executive Engineer’s monthly progress
report a list of breaches will be submitted, canal by canal, with
columns showing date of occurrence and cost of closure. The return
should be on the attached form G.[63] The Subdivisional Officer should
also submit this form to the Executive Engineer.

  [63] Not printed. The form differs slightly from a form prescribed by
  the Chief Engineer for general use in the Province.


10. =Estimates.=--The cost of breaches is not to be charged to
maintenance estimates. At the close of each month the Executive Engineer
should submit or sanction an estimate, accompanied by the breach
reports, for closing any breaches which have occurred and making up the
banks.


11. =Breaches in the Flooded Area near Canal Heads.=--These may be of
special importance. It may be impossible to do any good and money may be
uselessly spent. In any such cases the Subdivisional Officer should at
once proceed to the spot and the case should be reported by wire to the
Executive Engineer and, if necessary, to the Superintending Engineer.


12. =Breaches in Flood Embankments.=--The Subdivisional Officer must at
once proceed to the spot and the case be reported by wire to the
Executive Engineer and Superintending Engineer. The Breach Report forms
can be submitted partially filled in at the earliest possible moment and
a complete form afterwards.


APPENDIX E.

SPECIFICATION FOR BUSHING.

(See page 139.)

1. The object of bushing is to form a silt berm and thus prevent or stop
the falling in of the banks.

2. The branches must be thickly packed in order that the water among
them may become still, and also in order that they may not be shifted by
the stream. If thickly packed, the pegs required will also be fewer.
Most of the branches should be leafy and freshly cut, but, mixed with
these, there may be a proportion of kikar or other leafless branches.
Frequently it is possible to utilise jungle trees of small value,
bushes, scrub jungle, or even long grass.

3. Except when the bushes are to be very small or the length to be
bushed very short, the proposed line for the edge of the berm should be
marked out by long stakes driven in the water at fairly close intervals.
Otherwise the work may be badly done and the berm formed imperfect and
out of line.

4. As the berm formed is not likely in any case to be perfectly
straight, and as subsequent additions to it will be difficult, while
trimming it will be easy, the bushes should extend slightly beyond the
line of the proposed berm. Care should be taken that the lower branches,
which cannot be seen when once submerged, are long enough.

5. The branches should be piled up to above water-level, so that, as
they settle, they will assume the position desired, but to lay them high
above full-supply level on the slopes is useless and wasteful. If the
pegs have to be driven at a high level, the branches should be attached
to them by thin ropes or twine. Long pegs standing up high above the
ground are also wasteful. The pegs should as far as possible be kept in
line and their heads at one level.

6. If bushing is begun during low supply, it need not, at first, extend
up to full-supply level. More branches, freshly cut, can be added as the
supply rises. In any case it is generally necessary to make some
additions to bushing from time to time, and this should be explained to
contractors and others when fixing the rates.

7. If the trees from which branches are cut are in desirable places, the
branches should be cut with judgment; but where trees are in places
where they should not be (_e.g._, on the inside slopes of the channels),
all the branches may be cut off. The trunk may be left temporarily in
order to supply more branches.


APPENDIX F.

ESCAPES.

(See page 9.)

There are no definite rules regarding the capacity of the escapes to be
provided on a canal. On some canals in dry tracts of country the
discharging power of the escapes is a mere fraction of that of the
canal. In other cases it is about half that of the canal. In a district
liable to heavy rain an escape, say at a point where a canal divides
into branches, should be able to discharge about half of the main canal
supply. On branches, escapes, if provided at all, usually discharge into
reservoirs, and their period of working is very limited: it may be only
twenty-four hours.

On distributaries, escapes are seldom provided. It has been suggested,
in connection with modules, that the people irrigating from each
watercourse should be responsible for disposing, by means of it, of a
certain quantity of surplus water. This would be too rigid a rule. On
some watercourses there is much waste land or land under rice
cultivation; in such cases surplus water can be passed off without
damage. The canal subordinates are fully cognisant of such cases, and
they arrange accordingly. In other cases surplus water would do some
damage; but on nearly every distributary the full supply, even when
there is no demand for water, can be got rid of for a few hours, or even
more, without a breach occurring.

Escapes at outlets, in connection with modules, can be arranged by means
of waste weirs or by means of Gregotti’s syphons (_sifoni
autolivelatori_). The following is an abridged translation of part of a
pamphlet by Gregotti:--

  The figure represents one of the syphons installed in the “Centrali
  Milani.”

  A is the supply basin of the “Centrali,” which ends in the syphon B.
  The latter is constructed with mouthpiece of rectangular section _a_,
  which is submerged in the basin A. A weir divides the mouthpiece of
  the syphon from the descending branch, _c_, of the same, also
  rectangular in section. The weir crest is at level _dd_, from 2 to 7
  cm. below the maximum level of water surface which it is desired not
  to exceed in the supply basin.

[Illustration: FIG. 28.]

  The descending branch, _c_, has at its base a small tank _e_, which
  forms a water seal. The syphon is completed by a tube _f_, which is
  attached to the intake branch of the syphon and which ends at a level
  of 2 to 7 cm. above the previously mentioned surface _dd_.

  As soon as the water surface in the supply basin tends to rise above
  the plane _dd_, a filament of water, in falling over the weir _b_,
  pours down the descending branch _c_, and when the water has risen
  from 2 to 7 cm. above the crest of the weir, the thickness of the
  falling stream has become such that it is able, by lapping, with a
  wave-like course, the wall _gg_, to extract the air that has become
  enclosed in the syphon, and which cannot be replaced because the space
  in which the stream acts is closed at its base by the water in the
  tank _e_; and at the top also the aeration tube is closed by the rise
  in the water surface of the supply basin. From this point the syphon
  action quickly becomes fully established and begins to give its full
  discharge.

  The discharge that is given is equal to that of an orifice in a thin
  partition if certain limitations are allowed for between the fall used
  in the syphon and the height of the arch, that is, the distance from
  the crest of the weir to the inside roof of the syphon.

  The discharge is given by the formula

  Q = μA√(2_g h_).

  Q = discharge of syphon in cubic metres per sec.

  μ = a coefficient of reduction of discharge which varies between wide
  limits.

  A = the minimum cross-sectional area of the syphon in square metres.

  _g_ = value of acceleration due to gravity.

  _h_ = the fall, or the difference of level in metres between the water
  surfaces in the supply basin A and in the small tank _e_.

  As soon as the supply basin surface falls, the opening of the aeration
  tube becomes uncovered and air is drawn into the syphon. But until the
  surface has fallen some centimetres the supply of air is not
  sufficient to cause the syphon action to stop completely, and thus the
  escape varies gradually from the maximum discharge to zero as the
  water surface falls a few centimetres till it reaches its original
  level.

  In certain cases it is possible to do without the aeration tube,
  especially when the fall used in the syphon is not great and when it
  is possible to arrange matters so that the velocity of the water
  flowing past in front of the syphon is small.

  The syphon with a width of 3 metres escapes 8 cubic metres per sec. of
  water.


APPENDIX G.

GAUGES.

(See Chap. III., Arts. 2 and 3; also see _Hydraulics_, Chap. VIII., Art.
5, and Appendix H.)

1. The gauge should be placed on that bank and facing in that direction
which enables it to be most conveniently read by the gauge reader and by
officials passing the place.

2. The gauge should be of enamelled iron secured by copper screws to a
post of squared and seasoned wood which is either driven beforehand[64]
into the channel or spiked to a masonry work. Even in the deepest
channel a long enough post can be arranged for. A masonry pillar is not
necessary. The post may be rectangular in cross-section, with upstream
and downstream edges cut sharp. This prevents, or greatly reduces, the
heaping up of water at the upstream side and the formation of a hollow
downstream. If the “Ward” gauge of two vertical planks is used, the
planks should meet at an acute angle, not a right angle, and not be
wider than 7 inches each.

  [64] Driving after the gauge is attached may loosen or break the
  screws.

3. The top of the gauge should be slightly above the highest probable
water-level. The post should extend up to the top of the gauge.

4. If ever the graded bed of the channel is altered the zero of the
gauge should be altered. There may be some risk of confusion at first,
but it can be avoided by exercising due care and making notes. The
levels of the old and new zeros should be recorded.

5. A gauge at a distance from the bank is objectionable. It collects
jungle, cannot be properly read, and is liable to be damaged by floating
logs or boats. A gauge should be as near as possible to one bank or the
other. If the bank is vertical, the gauge should be quite close to it.
If, owing to silt deposit, the gauge is dry at low supply, the deposit
can be removed by the gauge reader.

6. Every regulator should be given a name, generally that of a
neighbouring village and not that of a channel, and the gauge book
headings should be drawn up in an intelligent and systematic manner.
Each main channel should be entered in order, and each regulator on the
channel--together with the head gauges of all channels which take off
there--should be entered, commencing from upstream. A specimen is given
on page 109. Thus the head gauge of any branch appears in the register
of the main channel from which it takes off, other gauges on the branch
appearing in the register for the branch. And similarly as regards a
distributary which has gauges other than the head gauge.

7. Each gauge reader should be supplied with a register, each page
having, besides the counterfoil, as many detachable slips--marked off by
perforations--as there are officials--usually the Subdivisional Officer,
zilladar and suboverseer--to whom daily gauge reports are to be sent.
The titles and addresses of these officials are printed on the backs of
the respective slips. The slips and counterfoil have printed on them a
form--similar to part of the specimen shown on page 109--showing the
names of all the gauges read by that particular gauge reader, so that
he has merely to fill in the date and readings, tear off the slips and
despatch them. The posting of the register in the subdivision is
facilitated if each gauge has a number and if the corresponding numbers
are printed--besides the names--on the gauge slips. If the gauge reader
does not know English, the headings of the slips are printed in the
vernacular. If the gauge readings are telegraphed, there may be only one
slip--besides the counterfoil--which is sent to the telegraph
signaller.


APPENDIX H.

GIBB’S MODULE.[65]

(See p. 164.)

  [65] This description has been supplied by Glenfield & Kennedy,
  Kilmarnock. The modules can, it is understood, be obtained from them.

The attributes of a perfect module are many and varied, but in Gibb’s
module they have all been successfully embodied in what is probably the
simplest piece of apparatus of its kind ever devised. The following
summary of the characteristics of Gibb’s module is, therefore,
equivalent to an enumeration of the attributes of a perfect module:--

  Gibb’s module

  Cannot be tampered with,                }
  Cannot get out of order,                } since it has no moving
  Silt or other solid matter in the water } parts, and because of its
  cannot affect its action,               } extreme simplicity.
  Requires no attention,                  }

  It is accurate,                     } being designed on scientific
  Works with very small loss of head, } hydraulic principles.

  It is portable, and can be erected at any desired site very simply and
  easily.

  It is strong and durable.

  The range of variation of both up- and downstream water-levels through
  which the discharge remains constant is more than sufficient to meet
  all the requirements of irrigation canals.

  The sufficiency of the delivery can be ascertained at a glance.

  The water can be drawn from any desired depth in the parent channel.

  When desired, means are provided whereby the supply can be closed or
  opened at will.

  Means are provided, if desired, for a sudden increase of discharge
  when the upstream water-level exceeds a certain limit, so that surplus
  water, which might endanger the safety of the canal, is allowed to
  escape into the branch whenever the danger limit is reached. The
  upstream water-level at which escapement begins can be fixed in
  accordance with the requirements of each site, and the action of the
  escape notch is independent of the opening and closing of the module.

  No designing or calculations are required. These have already been
  worked out. Known the discharge required, the module is supplied
  complete and ready for setting in position in the canal bank.


HYDRAULIC PRINCIPLE.

The entire absence of moving parts is the chief feature of Gibb’s
module; the water simply regulates itself by using up all the excess of
energy over and above that required to discharge the correct supply of
water. The way in which this takes place will be understood from the
following analogy:--

We all know that when we stir tea in a cup so as to make it spin, the
liquid rises at the rim of the cup and curves down into a depression in
the middle, and the greater the spin the more marked this effect is. It
is, we know, the centrifugal force produced by the spin that makes the
tea remain high at the rim of the cup. If, while the tea is thus
spinning, a teaspoon is held so that it dips slightly below the surface
of the liquid near the rim, it will obstruct the flow of the outer
portion of the liquid, which will fall in towards the depression in the
middle. The reason for this, of course, is that the centrifugal force is
absorbed when we interrupt any part of the spin with the teaspoon; hence
the liquid must fall, and we know that when liquid falls it uses up
“head” or energy.

In Gibb’s module a similar action is made to take place in a steel
chamber, semicircular or spiral in plan, through which the water flows
in a semicircular path instead of circulating round and round as in the
teacup. The surface of the stream, however, assumes the same form as it
does in a cup, because it flows under the same conditions. Across the
chamber are fixed a number of vertical steel diaphragm plates which take
the place of the teaspoon in the above analogy. The lower edges of these
plates are of such a shape, and they are fixed at such a height from the
bottom of the chamber, as to allow a stream of just the correct required
discharge of water to flow under them without interference. But if,
owing to an increase of head caused by a rise in the upstream
water-level, the water tends to rise higher at the circumference of the
chamber, then the water at the surface of the stream strikes against the
diaphragm plates, and its centrifugal force being absorbed, it will fall
in towards the centre just as happened in the teacup when the spoon was
used in place of these plates. In this way the excess head that caused
the additional rise of water at the circumference is used up by the fall
back towards the centre. The full capacity of the semicircle or spiral
for using up excess head or energy in this way is made available by the
use of a sufficient number of diaphragm plates fixed at suitable
intervals. When the range of head to be dealt with is not large, then a
semicircular chamber is sufficient; but for large ranges of head the
chamber is made of spiral form so as to lead the water round a complete
revolution or more, as may be necessary.


STRUCTURAL DETAILS.

Fig. 29 shows the general form and structure of the type of module
suitable for irrigation. Fig. 30 is from a photograph.

The working chamber or shell A is constructed of mild steel plating
securely riveted to a framework of angle steel, and the semicircular
form of the shell with the rigid diaphragm plates B B riveted to the
walls makes a very strong structure, and ensures durability.

The “leading-in” bend C is of cast iron strongly bolted to the steel
shell, and is so designed as to deliver the water into the module
chamber in a completely established vortex condition.

The socket D on this “leading-in” bend is made so as to allow of
considerable latitude in the vertical alignment of the straight
leading-in pipe, so that the water can be drawn from any desired depth
in the parent channel, and the proportion of silt drawn off is thus
brought under control.

[Illustration: -- END ELEVATION. --

-- PLAN. --

-- FRONT ELEVATION. --

FIG. 29.--Details of Gibb’s Patent Module.]

Grooves E E and a shutter F, as illustrated, for closing off the flow
through the module, are provided, if required, but all modules are not
fitted in this way, because many irrigation authorities consider it
undesirable to provide the consumers with unrestricted facilities for
closing off their supplies without previously giving notice of such an
action.

[Illustration: FIG. 30.--The Completed Module (Open Type for Low
Heads).]

An escape notch H is provided in the position indicated when desired. It
may, however, be found difficult to determine beforehand the upstream
water-level at which it is necessary to allow this escape of surplus
supply, so that it is generally more satisfactory to cut the escape
notch after the modules have been installed and actual experience has
indicated a suitable level for the notch crest.

In the standard type of module for irrigation purposes the top of the
module chamber is completely open, as shown, and this is the type
generally recommended, as it is found that consumers have greater
confidence in an apparatus which hides nothing from them. To meet the
needs of special cases, however, a second type is also made in which the
chamber is completely closed and considerably reduced in height, being
thus specially suitable for sites where space is confined.

Pipes I, of diameter suitable for all sizes of modules, are also
supplied. These may either be welded steel or cast iron, as desired. An
18-feet length of pipe is usually found sufficient to bring the supply
through the canal bank to the module.

All modules supplied are treated with anti-corrosive paint, which
ensures the protection of the metal.


APPENDIX K.

KENNEDY’S GAUGE OUTLET.[66]

(See p. 168.)

  [66] See _Punjab Irrigation Branch Paper No. 12_, “Results of Tests of
  Kennedy’s Gauge Outlet.”

FIG. 31 shows a bell-mouthed orifice discharging into an air-space. The
jet springs across the air-space and traverses a gradually diverging
tube. Let _a_, A be the sectional areas of the stream at the air-space
and the downstream end of the tube respectively, and let V, _v_, and
P_ₐ_, P₁ be the corresponding velocities and pressures. Let resistances
be neglected. Since the pressure in the air-space is P_ₐ_,

  V = √(2_g h_₀)

or the discharge through the tube depends only on _h_₀ and not on _h_₁.

[Illustration: FIG. 31.]

By Bernouilli’s theorem,

   V²    P_ₐ_   _v_²   P₁
  ---- + ---- = ----- + --
  2_g_     W    2_g_    W

or

  P₁ - P_ₐ_   V² - _v_²
  --------- = ---------.
      W          2_g_

This quantity (since _v_ is small) is not much less than _h_₀ or
V²/2_g_. In other words, the water levels of two cisterns with an
air-space between them differ only a little, or _h_₁ is small.

The above case (two cisterns and air-space) is mentioned in
_Hydraulics_, Chap. V. The principle is simply that the velocity head at
the air-space is reconverted into pressure head by passing the stream
through a gradually diverging tube. In the absence of such a tube the
velocity head would be wasted by causing eddies in the downstream
cistern.

If the downstream cistern is a watercourse whose water-level is
considerably lower than that of the upstream cistern or distributary, V
is obviously unaffected. Also P₁ is obviously reduced. Therefore, by
Bernouilli, _v_ is increased, or the stream does not fill the expanded
tube and there are eddies in the tube. The water-level in the
watercourse may even be lower than the end of the tube. The discharge is
unaffected.

In practice there are, of course, resistances, but this fact does not
affect the general conclusions stated above. The minimum working head
(difference between the two water-levels) which gives a constant
discharge is greater than would be the case in the absence of
resistances. This “minimum working head for modularity” has been found
to be ·21 foot, ·42 foot, and ·61 foot, the corresponding values of the
“depression,” _h_₀, being respectively 1 foot, 2 feet, and 3 feet. When
the working head is less than the above, the discharge is less and it
depends on the working head. The depression should, according to
Kennedy, be about 1·75 feet, but it may be more.

The chief difficulty in using the gauge outlet as a module is that the
air vent can be stopped up. This converts the apparatus into a compound
diverging tube (_Hydraulics_, Chap. III., Art. 17). The discharge is, of
course, increased, and it becomes dependent at all times on the working
head. Another difficulty is that any rise or fall in the water-level of
the distributary (and such rises and falls may occur owing to silting or
scour, however carefully the discharge may be regulated) alters the
discharge somewhat, though not to the same degree as in an ordinary
outlet with a working head of, say, ·5 foot. In short, Kennedy’s gauge
outlet, or “semi-module” as it is sometimes called, can modify but not
do away with the variations of the discharges of outlets.




INDEX.


  Absorption, 16, 159.
  Alignment, principles of, 4.
  Alignment, centrality in, 5.
  Alteration in line, 59.
  Assiut Barrage, 11.
  Assouan Dam, 11.

  Banks, construction of, 138.
  -- protection of, 139, 175, 178.
  -- width and height of, 56.
  Banks and Roads, 53.
  Basin Irrigation, 11.
  Berms, 53.
  Bifurcations, 47.
  Bifurcation, head needed at, 45.
  Borrow pits, 55.
  Branches of Canals, 3.
  Breaches in Banks, 176.
  Bricks used for canal work in India, 88.
  Bridges, 8, 80, 87, 130.
  -- Skew, 29, 42.
  Bushing of banks, 178.

  Canal and branches, 20, 47.
  Canal, bed width of, 51.
  -- supplied from reservoirs, 3, 13.
  -- inundation, 1, 45, 79, 127, 156.
  -- perennial, 1.
  Capillarity, 16.
  Cattle Gháts, 81, 173.
  Cement for lining channels, 160.
  Chainage, 93, 118.
  Channels, alterations in, 97.
  -- enlargement of, 97, 139.
  -- gradients of, 50.
  -- side slopes of, 52.
  Colonization Schemes, 64.
  Command, 2.
  Commanded area, 4.
  Contour lines, 37.
  -- plan, 26, 36, 63.
  -- survey, 37.
  Crops, failure of, 103, 142.
  -- kinds of, 101.
  Culturable commanded area, 26, 113.
  Curves and bends in channels, 8, 139.

  “Delta,” 22, 110.
  Deputy Collector, 96.
  Designs and Estimates, 60.
  Design of canals, 2, 26, 30, 47, 147, 156.
  Discharge of canal during rabi, 52, 118.
  Discharge observations, 107.
  Discharges of Punjab rivers, 145, 157.
  Discharge tables, 106.
  -- through an outlet, 61.
  Distance marks, 93.
  Distribution of water, 14, 118, 125.
  Distributaries, 3, 20, 44, 46.
  -- best system of, 71.
  Distributary, bed width of, 68.
  -- design of, 60.
  -- height and width of banks, 68.
  -- kharif, 156.
  -- longitudinal section of, 69.
  -- major and minor, 41.
  -- off-take of, 51.
  -- remodelling of, 128.
  -- side slopes of, 69.
  -- strip of land for, 69.
  -- with three fourths full supply, 45, 68, 166.
  Divide Walls, 33, 169.
  Divisions, canal, 96.
  Drainage, 10.
  Drainage Crossings, 8, 156.
  Duty of water, 21, 25, 39, 148, 153, 154.
  Duty, improvement of, 24, 102, 158.

  Eastern Jumna Canal, 31.
  Efflorescence called “Reh,” 15.
  Egypt, irrigation in, 11.
  Embankments, 9, 33, 156.
  Escapes, 9, 100, 180.
  Estimates for work, 59.
  Evaporation, 16.
  Executive Engineer, 96.
  Extensions of canals, 127.
  Extra land, 58.

  Falling Shutters, 32.
  Falls, 8, 81, 87.
  -- incomplete, 87, 130.
  -- notch, 86.
  Field book, 101.
  -- map, 101.
  -- register, 101.
  Final line, 59.
  Flow and lift, 11.
  Full supply duty, 64.
  Full supply factor, 64.

  Ganges Canal, 31.
  Gauges, 10, 103, 104, 183.
  Gauge reader, 96, 98, 105, 184.
  Gauge reading, 105, 121.
  -- register, 105, 106, 108, 111.
  Gibb’s module, 164, 186.
  Guide banks, 35.

  Head for distributary, 82, 83.
  Headworks, 2, 30, 98, 99, 137.

  Indents for water, 98, 108, 110.
  Inundation canals, 1, 45, 79, 127, 156.
  Irrigation boundaries, 33, 129.
  -- in various countries, 1.
  -- registers, 113.
  -- unauthorised, 101.

  Kennedy’s gauge outlet, 168, 193.
  -- Rules for channel design, 48.
  Kharif or Summer Crop, 23.
  Kutter’s co-efficients, 51.

  Lift irrigation, 11, 142.
  Lime for making channels watertight, 162.
  Longitudinal section, 69, 130.
  Losses of water in channels, 16, 38, 159.
  Low supplies, 118, 123.
  Lower Chenab Canal, 25, 144.
  Lower Egypt, 11.
  Lower Jhelum Canal, 144.

  Maintenance work, 138, 171, 174.
  Marginal Embankments, 9.
  Masonry works, 29, 80, 89.
  -- -- large scale site plan, 89.
  -- -- type designs, 89.
  Mills, 8.
  Minors, question of desirability of, 75.
  Modules, 162, 186.

  Navigation, 12.
  Needles and horizontal planks, 85.

  Oil for lining channels, 160.
  Older Indian canals, 10, 68, 98.
  Outlet, discharge of, 61.
  -- registers, 113.
  Outlets, 15, 61, 66, 67.
  -- applications regarding, 140.
  -- design of, 76.
  -- on inundation canals, 79.
  -- on older canals, 68.
  -- positions of, 65.
  -- remodelling of, 131.
  -- register of, 113.
  -- size of, 114, 134.
  -- temporary, 78.
  -- variability of duty on, 66.

  Parapets, width between, 77.
  Patwari, 96, 101.
  Percolation, 16.
  Perennial Canals, 1.
  Pitching, 90.
  Plan, large scale, 59.
  Postal system, 97.
  Profile walls, 91, 94.
  Project, sketch of, 26.
  Proportion of land to be irrigated, 27, 156.
  Puddle for lining channels, 160.
  Punjab, projects for canals in, 144.
  Punjab rivers, 145, 147.

  Quarters for regulating staff, 88.

  Rabi or winter crop, 23.
  Railings, 88.
  Rain, 9, 22, 100.
  Ramps, 88.
  Ratio of bed width to depth, 50.
  Reduction in size of channel, 128.
  Registers, irrigation, 113.
  Regulation of supply, 103, 121, 127.
  Regulators, 7, 80, 84, 184.
  -- permissible heading up, 85.
  Remodellings of channels, 127.
  -- of outlets and watercourses, 131, 134.
  Rest Houses, 95.
  Reservoirs, 13.
  Rules for designing canals, Kennedy’s, 48.

  Scheme, cost of, 28, 59.
  Sides, falling in of, 139.
  Sidhnai canal minors, 41.
  Silt, clearance of, 97, 138, 139.
  -- deposit, 15, 97.
  -- trapping at Headworks, 47.
  Silting and scouring, 15, 48, 98, 139.
  Sirhind Canal, 19, 144.
  -- -- silting in the head reach of, 98.
  Soil, water-logging of, 10, 24, 102.
  Spoil Banks, 52, 57.
  Subdivisions, canal, 95.
  Subdivisional officer, 96.
  Suboverseer, 96.
  Superintending Engineer, 96.
  Supply carried, 100.
  -- distribution of, 14, 118.
  -- mean and full, 27, 46, 122.
  -- regulation of, 103, 104, 106, 127.
  Syphons, 7, 71, 87, 181.

  Tailing of one channel into another, 40.
  Telegraph, line of, 97.
  Training of rivers, 33.
  Trial lines, 58.
  Trial pits, 58.
  Triple canal project, 144.
  Tunnels, 13.
  Turns, or rotational periods of flow, 14, 118.
  Type cross sections, 56.

  Under-sluices, 32.
  Upper Bari Doab Canal, 19, 144.
  -- Chenab Canal, 33, 144.
  -- Egypt, 11.
  Upper Jhelum Canal, 50, 144.

  Velocity, 12, 50.
  Village lands, 62.

  Watching banks, 175.
  Water, payment for, 12, 100, 102, 142, 143.
  Water level, fluctuation in, 100, 124.
  Watercourse, limit of size of, 74.
  Watercourses, 4, 20, 65.
  -- applications regarding, 140.
  -- for trees, 58.
  -- remodelling of, 131.
  -- with poor command, 67, 133, 166.
  Waterings, 11, 24.
  Water-logging of the soil, 10, 24, 102.
  Wave, travel of, down a channel, 124.
  Western America, canals in, 12.
  -- Jumna Canal, 31, 39.
  Wing Walls, 89.
  Works, arrangement of, 89.
  -- two or more close together, 89.
  -- urgent repairs of, 137.

  Zilladar, 96.


Harvey & Healing, Printers, Manchester Street, Cheltenham.




  Transcriber’s Notes


  The inconsistent use of periods after Roman numerals has been
  retained; other inconsistencies (spelling, hyphenation, formatting and
  lay-out) have been retained as well, except when mentioned below.

  Depending on the hard- and software used and their settings, not all
  elements may display as intended. Some of the tables are best viewed
  in a wide window.

  Page 21: The equation does not agree with the calculations given.

  Page 66, Fig. 11: There are two illustrations labelled Fig. 11, the
  hyperlinks point to the appropriate illustration.


  Changes made

  Obvious typographical errors have been corrected silently. Footnotes
  and illustrations have been moved out of text paragraphs. Some tables
  have been re-arranged or split; in several tables, the data alignment
  has been standardised.

  Page 18, table, Total of second column: 8·93 changed to 8·01
  Page 39: Kutters changed to Kutter’s
  Page 93: marked out changed to marked at
  Page 69: 3 Depth of digging changed to 13. Depth of digging
  Page 109, first average ·1 changed to 4·1
  Page 117: Net Areas Irrigated in Areas changed to Net Areas Irrigated
  in Acres
  Page 150: Cusecs. added as in similar tables
  Index: Cattle Ghats changed to Cattle Gháts; Line for making ...
  changed to Lime for making ...; Lower Chenal Canal changed to Lower
  Chenab Canal.







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