EMBANKMENT, a large body, mound, or bank of earth, constructed or thrown up in different ways, according to cir eumstances. Embankments are of various kinds, aceoyding to the purposes for which they are designed, as 1:Aitway EMBANKMENTS, which carry a line of railway over valleys and low ground at the elevation required for the level of the rails ; CANAL EMBANKMENTS, for confining the water of a canal or reservoir, or upon which a canal-or aqueduct is formed ; and EMBANKMENTS constructed with the view of guarding, protecting, and defending lands on the borders of the sea, rivers, and lakee, from being inundated and injured by them, and for reclaiming lands from the sea.
We shall treat first of the latter description of embank ments. These are of different kinds and forms, according to the nature of the situations and the materials of which they arc constituted. In embanking against the sea and large rivers, where the slopes next them are naturally gentle and easy, they are mostly of the earthy description, being well put together, and covered on the surf:tee with turf cut from the tough sward of the land in the neighbourhood ; but in cases where the banks, borders, and shores, are steep and bold, they are usually of a more bard and solid nature : as of stone, brick, gravel, sand, shells, and other similar sub stances, laid closel) in some sort of tenacions material, such as clay or mortar, and other matters of the sante quality. Timber is also frequently employed in their construction, in a variety of forms.
In works of this sort, very much depends upon the form in which they are constructed, and the nature and manage. meat of the materials made use of. In respect to the first it may be remarked, that banks of these kinds are com monly constructed with too narrow bases for the heights w hick are given them ; from which circumstance, the sides hich are opposed to the effects of the water become too steep and upright ; consequently, in cases of high tides or floods, they are utterly incapable of resisting their weight, which has equally a lateral and downright pressure. Besides this, there is another disadvantage attending this method of forming them, m hich is, that the floods, as well as the tides, in ebbing and flowing, have a more continued action on one part than would be the case, if the slopes were more gentle and gradual : consequently, they have a much greater tendency to break down and destroy the superficial parts of the banks. With some variations in the forms, most of the embankments in this country are, however, made in this way. They may succeed in some particular instances; hut, in general, it is found that breaches are frequently taking place in them, from the effects of the sea or floods, which are not capable of being filled up or repaired without considerable difficulty and trouble ; and which, if suffered to continue even for a short space of time, endanger the whole embankment.
The common form of embankment is shown at Figure 1, and the improved form pointed out at Figure 2.
The angles or slopes of these sorts of works are made very different in various cases ; but that shown in the above figure seems, in general, well calculated for the purpose of resisting the impression of heavy tides, or the waters of floods. The greater breadth they have, in proportion to their height, the more eflectual they must be in resisting the power of the waters which come upon them. In regulating the heights of embankments, it is necessary to ascot tain the greatest depth of water at the highest tides or floods ; making the summits of them about two feet higher than the points to which they rise at such times. By some, a less height than this above the highest mark of the tides or floods has, how ever, been considered sufficient ; but it is always proper to be on the safe side, as the consequences of an overflow are very serious.
In forming embankments with stones, or other similar materials, which, as has been seen, is essential in bold steep banks or shores, it is necessary that they be laid in proper materials. and he closely jointed next the sea, or the rivers, so as to be fully capable of resisting the entranee of water. Great care is requisite in doing this, or the hank mill not stand, for the water, insinuating itself between the openings, wid sink down among the stones, softening and loosening the clayey or earthy matters underneath, by which portions of them will be forced out and washed away. I lollows being formed in that way below, the stones naturally sink d()wn ; and the waters, rushing into the cavities with considerable impetuosity, quickly displaces others, and the whole embank ment is soon destroy ed. This very frequently takes place with the heads thrown across rivers, and such pay ed or cause wayed hanks as are formed with the view of protecting and preserving bold and open shores. Such shores are especially liable to be undermined and carried away by the washing operation of the waters which come against them. In order to render the embankments perfectly secure in such eases, they should be laid with good mortar, and be pointed with a strong cement. A good coat of gravel, in some cases of this kind, is even found far superior to paving with stones.