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

"Irrigation Works" by E. S. Bellasis. Published by Good Press. Good Press publishes a wide range of titles that encompasses every genre. From well-known classics & literary fiction and non-fiction to forgotten−or yet undiscovered gems−of world literature, we issue the books that need to be read. Each Good Press edition has been meticulously edited and formatted to boost readability for all e-readers and devices. Our goal is to produce eBooks that are user-friendly and accessible to everyone in a high-quality digital format.

• Language: English
• Publisher: Good Press
• Release date: Dec 23, 2019
• ISBN: 4064066123772

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E. S. Bellasis

Irrigation Works

The Principles on Which Their Design and Working Should Be Based, with Special Details Relating to Indian Canals and Some Proposed Improvements

Published by Good Press, 2022

[e-mail]

EAN 4064066123772

Table of Contents

PREFACE

CHAPTER I. INTRODUCTION

1. Preliminary Remarks.

2. General Principles of Canal Design.

3. Information Concerning Canals.

4. Losses of Water.

5. Duty of Water.

6. Sketch of a Project.

CHAPTER II. The Designing of a Canal.

1. Headworks.

2. The Contour Map.

3. Alignments and Discharges.

4. Remarks on Distributaries.

5. Design of Canal and Branches.

6. Banks and Roads.

7. Trial Lines.

8. Final Line and Estimate.

9. Design of a Distributary.

10. Best System of Distributaries.

11. Outlets.

12. Masonry Works.

13. Pitching.

14. Miscellaneous Items.

CHAPTER III. The Working of a Canal.

1. Preliminary Remarks.

2. Gauges and Regulation.

3. Gauge Readings and Discharges.

4. Registers of Irrigation and Outlets.

5. Distribution of Supply.

6. Extensions and Remodellings.

7. Remodelling of outlets.

8. Miscellaneous Items.

CHAPTER IV. The Punjab Triple Canal Project.

1. General Description.

2. Areas and Discharges.

3. Remarks.

CHAPTER V. Proposed Improvements in Irrigation Canals.

1. Preliminary Remarks.

2. Reduction of Losses in the Channels.

3. Modules.

APPENDICES.

APPENDIX A. DIVIDE WALL ON LOWER CHENAB CANAL.

APPENDIX B. SPECIFICATION FOR MAINTENANCE OF CHANNELS.

APPENDIX C. SPECIFICATION FOR MAINTENANCE OF MASONRY WORKS.

APPENDIX D. WATCHING AND PROTECTING BANKS AND EMBANKMENTS.

APPENDIX E. SPECIFICATION FOR BUSHING.

APPENDIX F. ESCAPES.

APPENDIX G. GAUGES.

APPENDIX H. GIBB’S MODULE.

APPENDIX K. KENNEDY’S GAUGE OUTLET.

INDEX.

PREFACE

Table of Contents

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 20th, 1913.

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IRRIGATION WORKS.

CHAPTER I.

INTRODUCTION

Table of Contents

1. Preliminary Remarks.

Table of Contents

—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.

Table of Contents

—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.

Map

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.

Example

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