A more economical mode, and one, therefore, suit• ed to a less extensive scale of operation, is to inter sect a sandy shore in all directions, with common dead, or wicker work hedges, formed by first driving a row of stakes six or eight feet into the ground, leaving their tops three or four feet above it, and then weaving among these stakes, branches of trees, or the tops of hedges. The Dutch are said to weave straw ropes, and thereby to collect mud in the man. ner of warping. This mode being little expensive, seems to deserve a trial in favourable situations ; and, in so doing, it must not be forgotten, that much depends on the immediate management of the sur face, after it is in some degree fixed. In an exten sive trial of this sort at present in progress, on the west coast of Scotland, under an English gentleman, seeds and roots are baked in a mixture of loam and dung in the gravel, and then formed into masses, and scattered over a sandy surface. These, from their weight, will not, it is thought, be moved by the wa ter or the wind ; but becoming more or less covered with sand, the mass will be kept moist, and the seeds and roots will grow, and, fixing themselves in the soil, will in time cover the surface with verdure. The experiment is ingenious, and we hope will be crowned with success.
Embankments for straightening the Course of Ri vers.—Where a river in a fertile valley is very cir cuitous in its course, land may be gained, and a more rapid efflux of the water produced, by straight ening its course. The best plan in general for ef fecting this is, to find an entirely new bed or course for the river ; otherwise, when it passes alternate ly through new soil, and through a part of its old bed, its action on surfaces which are so different in regard to induration ends, if great care is not taken, in holes and gulleys in the new bank, which require to be constantly filled up with loose stones thrown in, and left to be fixed by the pressure and motion of the water.
The embankment used in straightening the course of rivers is almost always the mound, with a clay wall in the centre, varying in width according to the depth of the different parts of the old bed of the ri ver which it has to intersect. The materials for these banks are obtained from excavations for the new bed.
The pier, called the Protecting Pier, is to be con sidered as a species of embankment, whose object is to prevent the increase of partial breaches made in the banks of rivers, by accidental obstructions dur ing floods. A tree or branch carried down by a stream, and deposited, or accidentally fixed or re tained in its banks, will repel that part of the stream which strikes against it, and the impulse (counter- acted more or less by the general current) will di rect a substream against the opposite bank. The
effect of this continual action against one point of the opposite bank is, to wear out a hole or breach ; and the protecting pier is placed so as to receive the im pulse of the substream, and reverberate it to the middle of the general stream. If this pier is placed very obliquely to the substream, as well as to the general stream, it will prove injurious to the op posite bank, by directing a subcurrent there as great as the first ; and, indeed, it is next to impos sible to avoid this ; so much so, that Mr Smeaton, in every instance in which he was consulted in cases of this sort, recommended removing the obstacle where that could be done, and then throwing loose stones into the breach. A perfect bed of a river would be s perfect half cylinder, and therefore we are decidedly of opinion that Mr Smeaton's mode is the best, as tending to maintain, as much as 'possible, this form. Mr Marshal (Treatise on Landed Pro poly) has treated on piers of this description a considerable length ; but a very little reflection will show, that they are more likely to increase than to remedy the evil they are intended to cure. We have seen the injurious effects of piers on the Tay and the Dee, and on a part of the Jed near Crafting they are so numerous, that the stream is, to use a familiar phrase, banded about like a foot ball, from one shore to the other; behind every pier an eddy is formed, and, if the stream does not strike it exactly, a breach in the bank. Many of these piers have in consequence, been taken down.
The use of such piers can only be justified where the obstruction, from ill-neighbourhood or some such cause, cannot be removed from the opposite bank; or where, as is sometimes the case, it emits from an island of sand or gravel thrown out by the river near its middle, and which, however absurd it may appear, the interested parties cannot agree as to who may remove it. The case of buildings also being in danger may justify such a pier for imme diate protection ; but, if such breaches are taken in time, a few loads of loose stones will effect a remedy without the risk of incurring or occasioning a greater evil.
Such piers are frequently constructed of wicker work ; either a mere wicker hedge projecting into the water, as is common where the rivers are of slow motion,—as in England, and particularly on the , Thames, Tame, and Severn ; or a case of wicker work filled with stones, as is common where the mo tion is rapid,—as in Scotland, and particularly on the Esk, Tweed, Tay, and Clyde.