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RECLAMATION OF LAND

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Originally appearing in Volume V22, Page 955 of the 1911 Encyclopedia Britannica.
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RECLAMATION OF See also:

LAND . The boundaries between See also:sea and land are perennially changing. In many sheltered bays and estuaries the sea is receding, while along other portions of the sea-See also:coast it is continuously encroaching. The same causes operate to produce both results: the See also:rivers carry down with them detritus and sediment from the higher ground; the sea, aided by See also:wind and See also:tide, is always eroding exposed portions of the seaboard; and even such lesser influences as See also:rain and See also:frost assist in disintegrating cliffs composed of softer strata. The See also:main See also:object of reclaiming land from the sea is to increase the See also:area of ground available for cultivation. Land which has been raised by See also:accretion nearly to high-See also:water level can be shut off from the sea by See also:works of a See also:simple and inexpensive nature, and the fresh alluvial See also:soil thus obtained is generally very fertile. Accretion in estuaries takes See also:place very slowly under See also:ordinary conditions. Although at any one See also:time the sheltered areas may be large and the See also:deposit of silt fairly rapid, not much permanent accretion will take place owing to the frequent shifting of the channels. Directly, 'however, a fixed channel is secured by See also:longitudinal embankments or training walls, accretion progresses rapidly and uninterruptedly by the deposit of sediment in the slack-water behind the embankments and at the sides of the See also:estuary; and this is especially the See also:case if the training works are raised to the level of high water, for this has the effect of restricting the greater See also:part of the scour of tide and fresh-water See also:discharge to the one fixed channel. The See also:rate of accretion varies with the shelter of the site and the amount of sediment carried by the water; but by degrees the foreshores, in the upper portion and at the sides of the embanked estuary, are raised sufficiently for samphire to make its See also:appearance, and, later on, a coarse grass. Ultimately the time arrives when the water may be altogether excluded by the construction of enclosing embankments; these must be raised above the level of the highest tide, and should have a See also:flat slope on the exposed See also:side, protected, in proportion to exposure and See also:depth of water, against the See also:face with See also:clay, sods, fascines or See also:stone pitching. In the intermediate stages of the See also:process outlined above much may be done to promote the growth of accretion, or warping as it is termed, and to ensure the fertility of the reclaimed land.

The deposit of warp is accelerated by anything which tends to reduce the flow and consequent scour of the ebb-tide over the See also:

foreshore: thus considerable See also:advantage will accrue from placing rows of faggots or sods across the lines of flow; and See also:banks, enclosing the higher portions of the foreshore, may often be constructed so as materially to increase the See also:period of stagnation, near high tide, of the silt-bearing water upon the See also:lower adjacent foreshore. The See also:light, fertilizing See also:alluvium only deposits in shallow water at high tide, and where there are no tidal currents. The final enclosure, therefore, should not be effected until this deposit has taken place. The enclosing works, also, should be so carried out that increasing shelter may favour the deposits of this alluvium during construction. A final and rapid deposit can sometimes be effected by making sluices in the banks: the turbid water is admitted near high tide, and retained until the whole of its silt has been deposited, the clear water being allowed to See also:escape slowly towards See also:low tide. Premature enclosure must be guarded against; it is more difficult, the cost greater, the reclaimed land is less fertile and, being lower, less easy to drain. The practice of reclaiming land in See also:British estuaries is a very See also:ancient one. The See also:Romans effected reclamations in the Fen districts; the enclosing of Sunk See also:Island in the See also:Humber was begun in the 17th See also:century, and now produces an See also:annual See also:revenue of something like £ro,000; large reclamations in the See also:Dee estuary took place in the 18th century; and, in See also:recent times, works have been carried out in the estuaries of the See also:Seine, the Ribble and the See also:Tees. In the reclamation of land adjoining the sea-coast, sites where accretion is taking place are obviously the most suitable. See also:Marsh lands adjoining the sea, and more or less subject to inundation at high tides, can be permanently reclaimed by embankments; but these, unless there is See also:protection from See also:sand See also:dunes or a See also:shingle See also:beach, require to be stronger, higher, with a less steeply inclined and better protected slope than is required in estuaries. The width of the See also:bank will generally prevent percolation of water at the See also:base; but if there is any danger of infiltration, owing to unsuitability of material, a central core of puddled clay or a See also:row of See also:sheet-piling should be employed. Waves over-topping the bank will quickly cause a See also:breach, and produce disastrous results; the height of the bank must, therefore, be calculated to meet the case of the severest on-See also:shore See also:gale coinciding with the highest See also:spring tide.

Undermining, caused by the recoil of waves on the beach, is liable to occur in exposed sites; this may be prevented by a See also:

line of sheet-piling along the See also:outer toe of the bank. Sea-coast embankments should not generally be constructed farther down the foreshore than See also:half-tide level, as the cost of construction and See also:maintenance would increase out of all proportion to the additional area obtained. It is, as a See also:rule, more economical to reclaim a large area at one time, instead of enclosing it gradually in sections, as the cost varies with the length of See also:embankment; it is, however, more difficult to effect the final closing of a bank, where a large area is thus reclaimed, on See also:account of the greater See also:volume of tidal-water flowing in and out of the contracted opening. The final closing of a reclamation embankment is best accomplished by leaving a fairly wide See also:aperture, and by gradually raising a level bank across its entire length. The enclosed area may be See also:left full of water to the height of the unfinished bank, or the tide-water may be allowed to escape and enter again by sluices in the finished sections. The embankments in See also:Holland are closed by sinking See also:long See also:fascine mattresses across the opening; these are weighted with clay and stone, and effectually withstand the scour through the See also:gap; the two terminal slopes of the finished sections are similarly protected. There are many examples of sea-coast reclamation: See also:Romney marsh was enclosed long ago by the Dymchurch See also:wall (see fig. r), and a large portion of Holland has been reclaimed from the sea by embankments (see fig. 2); the reclamation bank for the Hodbarrow See also:iron mines (see fig. 3) illustrates the use of puddled clay to prevent infiltration. The repair of a breach effected in a completed reclamation embankment is a more difficult task than that of closing thefinal gap during construction; this is owing to the channel or See also:gully scoured out upon the opening of the breach. When a maw , aO . 1 . See also:loo P.*.

FIG. r.—Sea-wall at Dymchurch.

End of Article: RECLAMATION OF LAND

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RECLUS, JEAN JACQUES ELISEE (1830-1905)

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