It has been remarked by 'Mr. Ileatson, whose observations on this subject we have heron/ noticed, that in the lakes or mires of the north, and the LO/IghS Scotland and Ireland, the business of embanking is both simple and easy. In these situations the waters generally subside during the summoner months, rising considerahly in m inter, and whenever the season is very wet. In particular eases the extent of surffice ti Inch is of erflowh in the w inter season, so for exceeds that which it covers during the summer, that it would be an object, and sometimes a considerable acquisition, to confine the water v. 'thin its summer boundaries, or to cut off some of its parts. To accomplish this the principal outlet must be carefully examined, and be considerably w ideued and enlarged : which will prevent the water from rising so high as was formerly the case. Where the levels will not admit of much depth Being had, or where the is of a rocky nature, and would of course be diffieult, and expensive to deepen, the breadth should be increased as much as possible, and all obstacles cleared away, that the water inay run freely in a shallow stream. \\ here it is required to ascertain with exactness, or, to fix with certainty, the future limits of the water, a section of the greatest quality running out during :1 flood should lie taken. :Suppose this section, for example, be 10 feet in width and I feet in depth, by making it -10 feet in width, the same quantity of water will not rise above 1 foot : consequently. by this me:ins alone, :; feet in height w ill be gained all round the lake, which. in case of embanking it, would he a great object. During the summer season, when water is lowest, is the most proper time for carrying on these, as well as other embankments. When, however, any materials are to lie brought from a distance, they may be laid down, or prepared at other seasons, with the exception of turf, which should always lie used as soon as possible after it is cut. The manner of conqrneting embankments of this kind may be sufficiently understood. from what has already heen said in the other description of embankments; observ ing, however, as a general ride, that when the materials on the spot will answer the purpose, they should invariably be made use of, although at the expense of digging a trench larger and deeper than would otherwise be neeessu•y. It should constantly be attended to, in executing all sorts of emhank ments, that time greatest care betaken to make them perfectly firm and solid, by continually beating them, and examining them carefully, during the whole of the time they are in a state of being formed.
The fidlowing, account of embankments on the Continent, is taken from the " Dictionary of Terms of Art," part of the very useful rudimentary treatises published by Mr.
"On the hanks of the Po. two si)rts of dykes are used to prevent the river from overflowing during the winter, or the flood season. They are called ' iu froldi,' w hen immediately upon the banks of the river, and 'in golcne,' when at any considerable distance, as it is sometimes found advisable to allow the river to spread over a large surf:ice of the adjacent valley, either for the purpose of admitting it to deposit the mud in suspension, or to allow it to lose its torrentaleharaeter,, The maintenance of the works of' these dikes is confided to the government engineers, who are under the control of a syndicate of the proprietors of the property most liable to be affected by inundations. 'When the river passes from one
state to another, as from Piedmont to Aludena, a mixed coin mission is charged with the joint superintendence.
" The Haarlem lake, besides the very remarkable steam engines described by Mr. Dempsey, merit: observation for the extensive works executed for the defence of the land, and ffi• the canals reserved for the navigation. The enclosure dike is 50,000 metres long, or rather more than 31 miles. It has two outfall dikes, which serve for the navigation, 0,000 metres, about 51, miles ; one half of which is '1))'" (1:11 feet' inch) wide at the bottom or floor line ; the other 43"' 20 (1,11 feet I() limbos.) The ordinary tides are at the flux, 2 feet 4 inches above the scale or dation line at Amsterdam ; at the rellnx feet inches below the same. datum : the difference between high and low water is then, on the average, about 5 feet. 'With violent winds from the N. \V., how ever, the tides rise some times ti feet 0 inches above the average. The tides of the 1', near the lake, are 4- 10' (or inches) and—" (o• 11 inches), giving a total variation of 1 foot 31 inches.
"The estimated cost of reclaiming the 1,5,000 hectares, was 5,000,000 of florins, or J:(167,000 Emdish, nearly about .C1:1 per acre. Previously to undertaking this colossal work, the 'Lied Plas, of 4,001) hectares superficial. (nearly 11,500 acres) 11:1,1 been reel tinted at a cost of :1,000.000 of florins, ur „f:250.000 ; not far from £•2 per acre. The heights. of the enclosure dike are -1- or — the datum line at Amsterdam, or the mean level of the sea in that port.
.Elli ha n kitt en I of the port of the A /nth"-, him and Ibla•lem railway.—The bottom part consists of treble ranges et Ihseines, tied down by Fades 1 metre apart from eentre to centre, :mil 0.•5' diameter; two double stakes at each end of the poles, and two ties in the intermediate distances. The interstices of the faseines and the spaee bet WI•el I the rows, are filled in with sand. The upper par, forming the encasement for the ballast. is made of three rows of treble •eseines, well staked and wattled together.
" A core of sand or clay, faced with step lascines, is made up to low-water mark. Upon this a bed of rushes, fastened down by stakes and wattles, is laid ; and the upper por tion of the bank is faced with litscines of a regular slope of I to I." Embankments against rivers may be divided into two kinds; namely, such as are tor preventing their encroaching on the adjacent lands, and for protecting those lands and the neighbouring level country from being overflown, when the water rises above its ordinary It may be remarked, that where the course of a river is it straight or nearly so, it hardly ever makes any encroachment upon its banks, unless, perhaps, in very large rivers, when they rise above their common level, either owing to an increase in the waters, or to their being, in sonic degree, affected by the tides. In case, the waves occasioned by a strong wind, where the river is wide, will moulder away the banks on that side upon which it blows, unless prevented in proper time. This may be done either by securing the bank properly with stones, or by driving a row of long piles pretty close together at a little distance from the shore, the piles being of such a length, and so driven, that their tops may be always above the highest rise of the water. It is surprising the effect that piles driven in this manner have in resisting the power of the waves in such situations.