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.
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.