E MB

380

EMB

mouth (which opens into the Western Ocean,) than in anyother part, and in its whole extent is extremely exposed tothe winds. It was proposed to construct here three embank-ments, the first 1,100 yards, the second 1,133 yards, and thethird 633 yards in length. The position of these banksj being fixed by careful measurements and soundings, the pro-i posed method of formation was as follows :j Each bank was to be 4 feet in perpendicular height abovethe highest spring-tides, which here rise to 18 feet ; and tohave a slope on the sea-face of 3 to 1, except in the giostexposed part, where the slope was to be 4 to 1. The materialsavailable for the work were stone, clay, earth and gravel,taken from the adjoining lands, and the banks were to befaced with rough stones on both sides, laid as close as possiblewith the edge outwards, in courses not exceeding 4 feet inheight. In the centre of each bank was to be built aj culvert of masonry, with proper sluices and flood-gates.These culverts were to rest on a foundation made bydriving piles into the soil, which from its alluvial character, could not be depended upon in itself. The sluices being self-acting, the drainage would be effected in the following manner,i At high water, it being supposed that the whole of the slobj (as it is termed in Ireland, ) is covered on the receding of the! tidal water, the sluices would shut of themselves, retainingI the water within the banks. When the flood-tide came on,the pressure on the sluice-gates from within, would preventi their opening to admit it, and the retained water would soonI evaporate, leaving the rich slob dry, and to be in a short timefit for agricultural purposes.

j The extent of the slob thus enclosed by these three wallswould be about 2,000 acres, and the value of it may bei estimated by the fact that a large quantity of land has alreadybeen reclaimed near this part of the Lough. This land now; lets at £5 per acre, and is considered the richest soil in theneighbourhood. Indeed, in every case, where a proper| selection of land has been made, and the works performedi judiciously, similar success has been the result.

| It has been remarked by Mr. Beatson, whose observations| on this subject we have before noticed, that in the lakes ori mires of the north, and the Loughs of Scotland and Ireland ,the business of embanking is both simple and easy. In thesesituations the waters generally subside during the summermonths, rising considerably in winter, and whenever theseason is very wet. In particular cases, the extent of surfacewhich is overflown in the winter season, so far exceeds thatwhich it covers during the summer, that it would be an object,and sometimes a considerable acquisition, to confine the waterI within its summer boundaries, or to cut off some of its parts.To accomplish this, the principal outlet must be carefullyexamined, and be considerably widened and enlarged ; whichwill prevent the water from rising so high as was formerlythe case. Where the levels will not admit of much depthbeing had, or where the ground is of a rocky nature, andwould of course be difficult and expensive to deepen, thebreadth should be increased as much as possible, and allobstacles cleared away, that the water may run freely in ashallow stream. Where it is required to ascertain withexactness, or to fix with certainty, the future limits of thewater, a section of the greatest quantity running out duringa flood should be taken. Suppose this section, for example,be 10 feet in width and 4 feet in depth, by making it 40 feetin width, the same quantity of water will not rise above 1foot : consequently, by this means alone, 3 feet in height will! be gained all round the lake, which, in case of embanking it,

| would be a great object. During the summer season, wheni the water is lowest, is the most proper time for carrying onj these, as well as other embankments. When, however, any

■ be

laid

materials are to be brought from a distance, they may ^down, or prepared at other seasons, with the excep a f ter itturf, which should always be used as soon as possibl e ^is cut. The manner of constructing embankmentskind may be sufficiently understood, from what has a ^ gerV .been said in the other description of embankments : | Jfl

ing, however, as a general rule, that when the materia s ^

spot will answer the purpose, they should invariably 0 ^

use of, although at the expense of digging a trenchand deeper than would otherwise be necessary. 11 i,.

constantly be attended to, in executing all sorts ol e |yments, that the greatest care be taken to make them P er - n ; n gfirm and solid, by continually beating them, and exathem carefully, during the whole of the time they arestate of being formed. t'nenb

The following account of embankments on the Lon j jgis taken from the “ Dictionary of Terms of Art,” pa(t overy useful rudimentary treatises published by Mr. ” ‘ , (0“ On the banks of the Po, two sorts of dikes are usprevent the river from overflowing during the winter, te ]y

Aa/i/I caaoArt Tltow orn Aollod < in fmlili 9 wflfiTl 101^^ ^ .«»

at

“ On the banks of the Po, two sorts of dikes are

he winter

flood season. They are called ‘ in froldi,’ when immupon the banks of the river, and ‘in golene,’ when - (0

considerable distance, as it is sometimes found a< ^ v,s ?. ce ntallow the river to spread over a large surface of the a J‘ ^valley, either for the purpose of admitting it to depo ^mud in suspension, or to allow it to lose its torrental cha , (0The maintenance of the works of these dikes is con ^the government engineers, who are under the contrsyndicate of the proprietors of the property most liab 0 , ieaffected by inundations. When the river passes n° ^state to another, as from Piedmont to Modena, a mixemission is charged with the joint superintendence. . alB -“The Haarlem lake , besides the very remarkable ^engines described by Mr. Dempsey, merits observati ^the extensive works executed for the defence of * ' g ] oSl jreand for the canals reserved for the navigation. Theen ^dike is 50,000 metres long, or rather more than 3 .^jon.It has two outfall dikes, which serve for the j* aV1 ? 4 Qf°9,000 metres, about 51 miles ; one half of which 1(131 feet 2 inch) wide at the bottom or floor line ; tae43 m 20 (141 feet 10 inches.) abo ve

“ The ordinary tides are at the flux, 2 feet 4 inches ^ e tthe scale or datum line at Amsterdam ; at the reflux, j,8 inches below the same datum : the difference betweeand low water is then, on the average, about 5 feet- ^violent winds from the N.W., however, the tides rlS ® j e3 of

times 6 feet 6 inches above the average. The_g 3 c

the Y, near the lake, are +16' (or 6 £ inches) an(or 9 inches), giving a total variation of 1 foot 3^ nic 1 .^eS,“The estimated cost of reclaiming the 18,000 ^ ^utwas 8,000,000 of florins, or £667,000 English , near y ^ i 0 l -p,£13 per acre. Previously to undertaking this colossathe Zind Plas, of 4,000 hectares superficial, (nearly ’ j n s,acres) had been reclaimed at a cost of 3 , 000,000 n - eor £250,000 ; not far from £22 per acre. The ^the enclosure dike are + or — the datum line at Amor the mean level of the sea in that port.” ,

Embankment of the flooded part of theTaarlem railway. —The bottom Dart consists of tieb ^

from centre to centre, and 0.25° diameter ; two

double

ofda* 0 ’

Haarlem railway .—The bottom part consists o. »*— a paof fascines, tied down by longitudinal poles 1 “.nL 6 stak"

e di» te

at each end of the poles, and two ties in the intern cedistances. The interstices of the fascines and th aI -t,between the rows, are filled in with sand. The upp ^sforming the encasement for the ballast, is made of tin i

of treble fascines, well staked and wattled together. ^ ^d 9 , j“ A core of sand or clay, faced with step fascines, 1 j