Index for River and Canal Engineering, the characteristics o

Summary:

"River and Canal Engineering" by E. S. Bellasis is a scientific publication written in the early 20th century. This work provides a comprehensive overview of the principles and practices involved in the engineering of streams that flow through open channels, tackling various aspects such as the hydraulic behavior of streams, the methods for controlling their flow, and strategies to combat issues like silting and scouring. The opening of the book sets the stage with a detailed introduction to River and Canal Engineering, emphasizing the importance of understanding open flowing streams. It outlines the structure of the work, which covers topics including rainfall statistics, the characteristics of stream behavior, methods of measuring discharge, and the effects of vegetation on water dynamics. The author stresses the need for accurate data collection concerning streams before undertaking any significant work, noting that variations in flow, sediment transport, and water levels play critical roles in stream management. This initial portion serves as a foundation for a deeper exploration of hydraulic engineering, providing valuable insights for engineers and students in the field. (This is an automatically generated summary.)

• The Project Gutenberg eBook ofRiver and Canal Engineering, the characteristics of open flowing streams, and the principles and methods to be followed in dealing with them.
• 8.Remarks.—Very much remains to be done in collecting and publishing information concerning the ratio of the discharges to the rainfall. By observing a fall of rain and the discharge of a stream before and after the fall, it is possible to ascertain the figures for that occasion, but they will not hold good for all occasions. Continuous observations are required. The chief obstacle is the expense. Not only have measuring weirs and apparatus for automatically recording the water-level to be provided, but the weirs would often cause flooding of land involving payment of compensation. The most suitable places for making observations are those where reservoirs for water-works exist or are about to be made.
• 5.A Canal with Headworks in a River.—In the case of a canal taking off from a river and provided with complete headworks, it is possible to do a great deal more. The case of the Sirhind Canal, already referred to (Chap. IV.,Arts. 5and6), is a notable example. The canal (fig. 6) is more than 200 feet wide, the full depth of water 10 feet, and the full discharge about 7000 cubic feet per second. In 1893 when the irrigation had developed, and it became necessary to run high supplies in the summer—July, August, and part of September—the increase in the silt deposit threatened to stop the working of the canal.In the autumn and winter, say from 25th September to 15th March, the water entering the canal is clearand much of the deposit was picked up by it, but not all. In the five years 1893 to 1897 inclusive, the following remedial measures were adopted. Increased use was made of the escape at the twelfth mile. This did some good, but there was seldom water to spare. In 1893 to 1894 the sill of the regulator was raised to 7 feet above the canal bed, and it was possible to raise it 3 feet more by means of shutters. This had little effect. The coarsest class of sand was ·4, and the velocity of the water, even of that part of it which came up from the river bed and passed over the sill, was over 2 feet per second, so that all sand was carried over. In 1894 to 1895 the divide wall, which had been only 59 feet long, was lengthened to 710 feet, so as to make a pond between the divide wall and the regulator,8but probably the leakage through the under-sluices was often as much as the canal supply, and the water in the pond was thus kept in rapid movement and full of silt. The canal was closed in heavy floods. This did some good, but probably the canal was often closed needlessly when the water looked muddy but contained no excessive quantity of sand. The above comments on the measures taken were made by Mr Kennedy when chief engineer. The above measures did not reduce the silt deposits, but the scour in the clear water season improved, probably because higher supplies were run owing to increased irrigation. The deposit in the upper reaches of the canal, when at its maximum about the end of August of each year, was generally more than twenty million cubic feet. From the year 1900 a better system of regulation was enforced, the under-sluicesbeing kept closed as much as possible, so that there was much less movement in the pond and much less silt in its water. By 1904 the deposit in the canal had been reduced to three million cubic feet, and no further trouble occurred.
• 4.Alteration of Depth or Water-Level.—When the width of a stream is altered, the depth of water—the gradient being supposed to be unchanged—must alter in the opposite manner. A narrowing of the channel by training necessitates an increase in the depth of water, and the same remark applies if an arm of the stream is closed. The increase in depth may be effected either by raising the water-level or by lowering the bed—as may be convenient—or both. If the bed is to be lowered and is of hard clay, it may be necessary to dredge it and, when this has been done, training may be unnecessary. If the bed is of soft mud, a dredged channel is likely to fill up again, and training alone will be the method to adopt. If the bed is moderately hard, say compact sand, it may be suitable to train the channel first and then to dredge if necessary. In any case, shoals of hard material may have to be dredged or rocks, whether these form shoals or lateral obstructions,to be blasted or otherwise broken up (Art. 2). In cases where it is desired to raise the water-level without any lowering of the bed, training is of course necessary. In any case in which the bed is likely to scour to a lower level than is desired, or if the bed is to be raised, the measures described inChap. V.,Art. 6, may be adopted, but they are hardly likely to be suitable and satisfactory in all cases.
• 5.Weirs with Sluices.—The long weirs built across Indian rivers below the heads of irrigation canals generally extend across the greater part of the river bed. In the remaining part—generally the part nearest the canal head—there is, instead of the weir, a set of openings or “under-sluices” (fig. 40) with piers having iron grooves in which gates can slide vertically. The piers may be twenty feet apart and five feet thick. The gates are worked by one or more “travellers,” which run on rails on the arched roadway. The traveller is provided with screw gearing to start a gate which sticks. When once started it is easily lifted by the ordinary gears. The gates descend by their own weight. The gate in each opening is usually in two halves, upper and lower, each in its own grooves, and both can be lifted clear of the floods. In intermediate stages of the river these gates have to be worked a good deal. (See alsoChap. V.,Art. 5.) Usually the weir has, all along its crest, a set of hinged shutters, which lie flat at all seasons, except that of low water in the river.
• 5.Prevention of Floods.—The extended use of field drains has, in recent years, done much to increase the severity of floods in England and other countries. One method of mitigating or preventing floods is the construction of reservoirs for storing the water. Reservoirs locally known as “washes,” formed by setting back the embankments, exist on the Fen rivers. One wash, on the Nene, below Peterborough, is 12 miles long and half a mile wide and is filled, in floods, to a depth of 7 feet and holds 1 inch of rainfall over the river basin, and this is found to be sufficient. Reservoir construction is, however, in most cases, impracticable owing to the expense. To store the water which is given by 1 inch of rain in the basin of the Thames, a reservoir would be needed 50 feet deep and covering about 7 square miles. It might cost £7,000,000.
• CHAPTER XIVTIDAL WATERS AND WORKS
• FOOTNOTES:
• THE FULL PROJECT GUTENBERG LICENSE
• Chapter 10

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