406 



THE FARMER'S MAGAZINE. 



RIVER EMBANKMENTS. 



An embankment is a mound, wall, or bank of earth, or 

 otlier materials, constructed for the purpose of protecting 

 lands from the inundations of rivers and water-courses, 

 and to confine streams of water within the bounds of a pre- 

 scribed channel. The term has been extended to fences of 

 any kind that are raised for the purpose of guarding low- 

 lands from being covered by floods of water, and the banks 

 of streams from being torn by currents and demolished by 

 the overwhelming force of waters. The two cases are most 

 common — protecting lowlands from being covered by inun- 

 dations, and the banks of rivers and streams from being 

 destroyed by the weight or rapidity of flowing and running 

 waters. 



Heavy falls of rain, and the melting of snows in hilly 

 and mountainous countries, produce an excess of water, 

 which enlarges the volume of rivers, rises above the banks 

 that contain the usual quantity, or overflows the adjoining 

 surface of grounds, and by remaining in stagnation on the 

 lauds, inflict a damage on the produce and value of the soU. 

 This damage equally ensues, whether the land be in an 

 arable condition, or used in a state of grass; for the 

 covering by water causes a low degree of temperature, which 

 continues for some time, and very much retards vegetation. 

 These grounds are mostly grazed by animals, during the 

 periods when the inundations of water are absent ; but in 

 many cases, the arable condition would be very profitable, 

 if the presence of the water could be averted. The low 

 position of the inundated grounds presents a formidable 

 barrier to the removal of tlie water, as the descent induces a 

 Bluggish motion, and retards the escape after the stream 

 has been directed into a proper channel. This obstacle has 

 exerted much influence on the operations of embanking, 

 and has very much perplexed the arrangements for the 

 purpose. When the fall of the ground aflbrds a quick de- 

 scent of the water, the process is comparatively very easy, 

 as it only remains to provide a proper channel, and to 

 direct the water into it. In other cases the channels are 

 overcharged, and burst by the bulk of the water, or are 

 always full, and throw back the water into the small 

 outlets. 



In order to prevent a superabundance of water from over- 

 flowing the flat grounds adjoining the course of rivers, the 

 first direction relieves the excess by providing a quicker 

 discharge into the ocean, which is the general receptacle of 

 all collections of water. This relief is prevented by the 

 flatness of the country permitting the waters of the ocean 

 to oppose a weight of opposition, by a deposit of mud 

 placed at the junction of the river and sea, and by the 

 tortuous course of the river producing a sluggish motion of 

 the waters — all produced by the level position of the 

 ground. The remedy being impossible in this way, the 

 next coiu-se provides a confinement for the waters within 

 certain bounds, till the bm-den is relieved by the gradual 

 discharge of outlet, after the cause has ceased from rains 

 and melted snows. A bank or fence is required for this 

 purpose. 



Embanking is based on very simple principles, but the 

 application of them requires both skill and experience. 

 The fundamental prmciple is, that a hquid presses on any 

 resisting soUd, not by any dimensions, or general proper- 

 ties of the fluid, but solely with a force proportionate to 



its depth. Hence when a perpendicular bank or wall is 

 opposed to a body of water, it has to sustain the pressure 

 of the depth of the body, and undiminished by any assist- 

 ance that can be given to it. This is a fixed law of fluids, 

 and carries along with it the simplest conviction of prac- 

 tice. It only remains to convert the deep pressure laterally 

 into a shallow depth vertically, and thus reduce the opposi- 

 tion from an impinging force into a rolling harmlessness 

 of motion. The force or weight of the water must roll 

 upon the bank or fence, and not impinge against it in depth ; 

 if water beats against any resistance, it will demolish it, 

 and cause an overwhelming destruction. It is a law both 

 of thecry and practice that the greater the slope of a bank 

 or fence, the more efiectually it performs the object of its 

 purpose, and its end as a resisting surface. There is no 

 precise rule for the degree of slope, because it depends on 

 the nature of the materials of the banks, and the degree 

 of exposure to the effects of water, This arrangement rests 

 with the judgment on special cases as they occur. 



Local experience will have ascertained in most cases 

 the height to which the greatest floods have been known to 

 ascend, and professional skiU and judgment will be re- 

 quired to determine the additional height that will be caused 

 by confining the overflowing water within a marked line of 

 boundary. It is a great blunder to confine a volume of 

 water within narrow bounds : water spread abroad is very 

 harmless; large collections, being confined and agitated, 

 burst all opposition, and sweep away eveiy obstacle in the 

 movements. At the same time an extent of ground may not 

 be wasted in giving room for water to flow : but a narrow 

 confinement must be avoided. 



The embankment or earthen mound that is raised in 

 order to confine waters from overflowing a level surface of 

 ground, must be directed in every possible case to throw 

 the volume of water into a mid- channel that tends to form 

 a straight line for the running stream. This line will be the 

 natural bed of the river when not swollen by an excess of 

 water, and into it and over it the volume must be directed. 

 The line of embankment must be directed, at every turn or 

 bending of its course to point the flow of the stream 

 into a mid-channel, narrowing for that purpose the space 

 that is allowed, but not so much as to throw a force of 

 water on the opposite bank, which would press on the em- 

 bankment, and overtop or demolish it. From both sides 

 of the river, the embankments must point the waters 

 into a mid-channel, by gradual narrowings and gentle 

 directions. 



The line of the mound or fence being determined by 

 local experience and professional skill, the erection of the 

 embankment is done with compacted clayey earth, rammed 

 hard in a moist condition, or made damp during the pro- 

 cess of being constructed. The front of the bank slopes 

 in three feet of base to one of perpendicular height, and 

 rises to a top of six feet in width, and of vertical height 

 that is at least one foot above the mark to which the floods 

 are calculated to lise. The back slope to the cultivated 

 lands is one foot or one-and-a-half feet of base to one of 

 vertical height, as it only forms a back support to the front 

 pressure, and does not sustain any direct opposition. The 

 front slope is made with great care, the damp materials 

 rammed into a compact hardness, and levelled with much 



