File:Principles of irrigation engineering, arid lands, water supply, storage works, dams, canals, water rights and products (1913) (14597700820).jpg

Identifier: cu31924073873089 (find matches)
Title: Principles of irrigation engineering, arid lands, water supply, storage works, dams, canals, water rights and products
Year: 1913 (1910s)
Authors: Newell, Frederick Haynes, 1862-1932 Murphy, Daniel William
Subjects: Irrigation Agricultural engineering
Publisher: New York : McGraw-Hill Book Company
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN

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al forordinary Ught earth. In some cases slopes may be made steeperthan 1/2 to i; in general, however, slopes steeper than this ex-cept in very firm rock have a tendency to slough, due to weather-ing, which results in a gradual filling of the channel. For earthen slopes, material is seldom encountered that willstand on a greater slope than i 1/2 to i. In that portion of thechannel forming the waterway, there is a tendency for the sidesto be gradually eroded or eaten away by the action of the water.The greatest erosion usually takes place a short distance below thesurface of the water and from this point the cutting graduallydecreases toward the bottom. The effect of this erosion is to forma rounded channel in which the sharp angle of intersection betweensides and bottom is eliminated. The general result is a flatteningof the sides of the entire bank, due to erosion and the weatheringof the material above where the erosion takes place. Banks con- 42 PRINCIPLES OF IRRIGATION ENGINEERING
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DESIGN AND CONSTRUCTION OF CANALS 43 structed with i 1/2 to i slopes after a few years are found to havebecome 2 to i or even flatter. When it is desired to maintain aroadway on the top of an embankment it is necessary to constructit somewhat wider than will be eventually required on accoimtof the reduction in width which follows the flattening of the slopes.Where the embankments are constructed with flat slopes the tend-ency for the top width to decrease is lessened. On the outer slopesof banks there is a less tendency to flattening, partly due to absenceof water against them and the consequent effects of erosion andsoftening of the material. In very light materials, however, windaction may have an important effect in reducing the outer slope.One of the dangers in too steep outer slopes, especially in new canals,is the tendency to slough or run when the bank becomes saturated.This danger may become serious in banks of considerable heightbuilt of light permeable material. The top widt

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