drying marl-pits, &c., it may be used to advantage in excavating a sufficient passage for the water, without opening a trench. In laying leaden pipes for the conveyance of water, it is also useful in making a hole 663

in which the pipe may be laid, without opening a cut on purpose. For tapping springs, or finding water at the bottom of a hill, either for the supply of a house, or for draining the ground, it may likewise be used with success; as the water of the spring, when hit on, will flow more easily and in greater abundance through a horizontal or level, than through a perpendicular outlet.

4318. The manner of using it is this:-Suppose a lake or pond of water, surrounded with high banks, to be emptied, if the ground declines lower on the opposite side, find the level of the bank where the perforation is to be made. There smooth the surface of the ground so as to place the frame nearly level with the auger, pointing a little upwards. It requires two men to turn the handles at top (a), in order to work it; and when the auger or shell is full, the rods are drawn back by reversing the lower handle (b). Other rods are added at the joint when the distance requires them. In boring through a bank of the hardest clay, two men will work through from thirty to forty feet in a day, provided there is no interruption from hard stones, which will require the chisel to be fixed on in place of the shell, and longer time to work through. If the length to be bored through is considerable, or longer than the whole length of the rods, a pit must be sunk upon the line, down to the hole, for placing the frame when removed, and the operation carried on as before.

CHAP. II.

Rivers or the Sea.

4319. Lands adjoining rivers or the sea are frequently liable to be overflowed or washed away, or to be injured by the courses of rivers being changed during great floods. These evils are guarded against by embankments and piers; or by these constructions joined to deepening or straightening the courses of rivers, and we shall therefore treat in succession of embankments and of improving the courses of rivers.

SECT. I. Embanking Lands from Rivers or the Sea.

4320. The great value of alluvial soil to the agriculturist no doubt gave rise to the invention of banks, or other barriers, to protect soils from the overflowing of their accompanying rivers. The civilised nations of the highest antiquity were chiefly inhabitants of valleys and alluvial plains; the soil, moisture, and warmth of which, by enlarging the component parts and ameliorating the fruits of the vegetable kingdom, afforded to man better nourishment at less labour than could be obtained in hilly districts. The country of Paradise and around Babylon was flat, and the soil saponaceous clay, occasionally overflowed by the Euphrates. The inhabited part of Egypt was also entirely of this description. Historians inform us that embankments were first used by the Babylonians and Egyptians, very little by the Greeks, and a good deal by the Romans, who embanked the Tiber near Rome, and the Po for many stadia from its embouchure. The latter is perhaps one of the most singular cases of embankment in the world.

4321. The oldest embankment in England is that of Romney Marsh; as to the origin of which, Dugdale remarks, "there is no testimony left to us from any record or historian." (History of Embanking and Draining.) It is conjectured to have been the work of the Romans, as well as the banks on each side of the Thames, for several miles above London, which protect from floods and spring tides several thousand acres of the richest garden ground in the neighbourhood of the metropolis. The commencement of modern embankments in England took place about the middle of the seventeenth century, under Cromwell. In the space of a few years previous to 1651, 425,000 acres of fens, morasses, or overflowed muddy lands, were recovered in Lincolnshire, Cambridgeshire Hampshire, and Kent; and let at from 2s. 6d. to 30s. an acre. (Harte's Essays, p. 54, 2d edit.) Vermuyden, a Fleming by birth, and a colonel of horse under Cromwell, who had served in Germany during the thirty years' war, was the principal undertaker of

Repertory of Patent Inventions, for January, 1826, and in the Bulletin des Sciences Agricoles, for November, 1827.

But

4322. Very little has been written on the subject of embankments, as a separate branch of art, by British authors. Dugdale's work is entirely historical and topographical. the writings of Smeaton, Young, Gregory, &c., contain the general principles on which is founded the art of embanking, and every other operation connected with water; and Beatson, (in Communication to Board of Agriculture,) Dr. Anderson, Marshal, and some others, have written on the practice of the art. The works of this sort constructed in our own times will be found described in the Agricultural Reports of the maritime counties, especially of Lincolnshire, by Arthur Young. We shall first submit some general remarks on the principles of designing embankments, and next describe the principal kinds of banks, with their application.

SUBSECT. 1. General Principles of designing Embankments.

4323. The theory of embanking, Marshal observes, is beautifully simple. The outward waters having been resisted by a line of embankment, and having receded, those that have collected internally are enabled, by their own weight, to open a valve placed in the foot of the bank, and effect their escape: thus securing the embanked lands from inundation, though beset on every side with water.

4324. The pressure of still water against the sides of the vessel containing it being as its depth, it follows, that a bank of any material whatever, impervious to water, whose section is a right-angled triangle, and the height of whose perpendicular side is equal to that of the water it is to dam in, will balance or resist this water, whatever may be the breadth of the surface of the latter; and therefore that, as far as width or extent is concerned, it is just as easy to exclude the Atlantic Ocean as a pond or a river of a few yards in width. 4325. Embankments may be considered in regard to their situation, direction, construction, and materials.

4326. The situation of the bank should be such that its base may not be unnecessarily exposed to the im. mediate action of the waves or the current; and where the quantity of water is limited, as in the case of land-floods in a particular river, the more room it has to spread, the less height and strength the bank will require; and the power of the current will be proportionably lessened. It is to be recollected, however, in all cases where the channel of the water is liable to be warped or filled up by sulliage, that the narrower the space is, in which the water is confined, the stronger will be its current, and the less silt will, in ordinary cases, be deposited.

4327. The direction of embankment should be free from sharp angles, so as to occasion the least possible resistance to the current, whether of a land-flood or the tide.

432. In the construction or form of the bank there are certain principles to be observed. Its height and strength ought ever to be proportioned to the depth and the pressure of water which it will have to sustain; and, to increase its firmness, the inner face should lean towards it, as a buttress. But it is on the construction of the outer face its strength, firmness, and durability principally depend. This ought to be made sloping, to a degree of flatness; for the twofold purpose of preventing resistance and taking off the weight of water. In difficult cases, the outer surface may form an angle with a perpendicular line of 45 to 60 degrees, according to the force to be guarded against, and the materials to be employed.

4329. The materials of the body of the bank (as well as of the inner face), where the foundation is sound and firm, and the bank can be carried up at a proper season, without great molestation from the water, may generally be the natural soil of the lands to be embanked; and, where merely the weight of stagnant or slowly moving water is to be guarded against, the outer slope may be of the same material. But where force, whether of waves or a strong current, will act immediately upon the bank, its outer face ought to be made proof against it; and its base should be particularly guarded, to prevent its being undermined; the most mischievous and irreparable disaster of embankments. Hence, when the foundation is not sufficiently firm, piles, timber, and masonry may be required, to ensure success; and no man ought to begin a work of this nature without attentively guarding it against every probability of miscarriage. 4330. A system of drains and floodgates is requisite for the purpose of freeing the embanked lands from internal waters.

4851. In designing and setting out the main drain, or discharging channel, on the outside of the embankment, there are points which require particular attention. The situation of the outfall, or mouth, with respect to the current of the water into which it opens, is of considerable importance. It ought to be such that the current of the water received will not warp up the channel of the drain; but such, on the contrary, as will tend to clear the mouth and keep the channel free. If it were not to preserve the requisite character of an elementary work, it might be deemed unnecessary to add, that the mouth of the discharging drain should be situated as low beneath the floodgate of the embankment as given circumstances and a prudent expenditure will allow; in order that, by inducing a sufficient current, the floodgate, as well as the mouth of the channel, may become free from obstructions. Against the open sea, or a wide estuary, where there is no disgorging channel, but where the waves reach the foot of the embankment, two floodgates may be required: one on the outer side, to sustain the force of the waves, and prevent their blowing up the inner works; the other within, to secure the passage the more effectually. The outer gate in this case is liable to be lifted with the agitation of the waves, and thereby to admit much water; but the inner valve, being in an undisturbed situation, effectually stops its progress.

4332. Where the discharge is made immediately behind a shifting beach, and especially where the floodgate is necessarily placed level with or beneath the general surface of the gravel bank, through which the waters have been wont to force a channel, the valve is liable to be buried, and the channel to be closed up by every spring tide, and by every gale of wind which sets in upon it; and cannot be kept free but by unceasing labour and expense. In an obstinate case of this kind on Lord Cawdor's estate, in Pembroke. shire, the discharging floodgate is defended by a covered channel, carried out through the line or ridge of beach into the sea; being made strong enough to sustain the weight of the heaviest breakers. This, it is true, has been effected at a great expense, but nevertheless, the improvement being of considerable magnitude, with great profit. In every case where an external valve is required, and where it is liable to be silted up, or loaded with sand or gravel, great attention to the outward channel is necessary, or some defence must be constructed; for the floodgate, when loaded, cuts off all communication between the pent up waters and the materials that impound them. They cannot, by loosening the obstructing matter, as

nature would otherwise direct them, force their way through it; nor, by surmounting it, can they wear down a channel, and thus set themselves at liberty.

4333. In ordinary cases, the outer floodgate may be guarded by a pile fence or jetty, run out from the foot of the embankment, across the known drift of the beach; and in such a manner as not to interrupt the outfall channel of the water; the gravel, &c. which such a safeguard may accumulate, being removed from time to time as occasion may require.

4334. The best construction of the flood-gate for the uses now under consideration is the common valve, hingeing at the top, swinging outward and falling into a rabbeted frame. In forming and hanging a floodgate of this construction, there are a few particulars worthy of attention. It should be made of seasoned wood, and ought to be double; the boards or planks of which it is formed being made to cross each other, to prevent its casting. It should fall truly, and fit neatly within a surrounding rabbet (to lessen the power of the waves to lift it); but not so closely or tight as to stick when swelled by moisture. To prevent this, as well as to give it additional tightness, its edges should not be square, but should bevel somewhat inward in the manner of a bung; the rabbet in the frame being made to answer it. In fixing the frame, it ought to be suffered to lean or batter inward; in which position the door will shut closer, and be less liable to the action of the waves in an exposed situation than it would if it were hung perpendicularly. It ought not, however, to lie so flat or heavy as to prevent the free escape of the internal waters. The floodgates or self-acting sluices, at Bar Loch embankment fall against a flat

664

surface. (fig. 664.) A writer in the Perth Miscellany states, (vol. i. p. 41.) that many of the tunnels in the embankments of the Tay have only wooden valves with iron hinges, and a lid of lead or iron nailed on for weight to keep them down. These, he says, are not to be depended on, and he has accordingly had some tunnels made of two inch plank with the end cut at an angle of 450 for the valve, and placed on a slope of 8 inches in 18 feet, the water being discharged on a broad piece of pavement. He had an iron plate "cast the exact size of the mouth of the tunnel, and about half an inch thick, with holes drilled two inches apart, and threefourths from the edge of the plate, for riveting a piece of saddler's leather, or shoemaker's brown sole, which extended at least two inches beyond the plate, and covered the whole end of the tunnel, the upper end of the leather nailed to the wood serving as hinges, and the edges of the mouth previously lined with the same material. Thus the strength of the tide never raises the valves, and completely prevents the water from getting in." (p. 42.)

4335. The internal waters which rise within or fall upon the area of the embanked lands, are to be collected by a main drain, continued upward from the floodgate; and furnished with branches to spread over every part of the field of improvement, so as to draw the water from every dip and hollow place as it collects, and thus free the surface effectually from stagnant water; saving such only as may be wanted for the use of pasturing stock.

4336. If alien waters have a natural and accustomed channel through the embanked area, it may be found necessary to raise a suitable bank at a proper distance on each side of the stream, in order to prevent its overflowing the area in time of floods. Where it is found that an outlet cannot be had low enough to free the area entirely from surface water, it is requisite (though no alien waters intrude) to form an embanked channel or reservoir, to gain the required outfall; and to throw the waters which lodge on the lower grounds into this receptacle, by a draining mill, of which there are a great variety of

constructions.

4337. An embanked channel, if the banks are raised high enough, or are placed wide enough asunder so as to contain a sufficient body of water, may have a further use, which, in some cases, may be of the highest importance to an improvement of this nature. For, by the help of folding floodgates, such as are commonly seen in use for the locks of navigable canals, placed at the lower end of this canal or reservoir, a body of water may be collected and rapidly discharged; by which easy means, not only the channel of the outer drain, but its mouth, if judiciously contracted, may from time to time be cleared from obstructions. Where alien waters of a good quality pass through the field of improvement, an embanked channel may be profitably applied in watering the lands; and where alien waters, which have not a natural or fortuitous passage through it can be commanded, and conducted to it at a moderate expense, they may prove highly beneficial, for either or both of these purposes.

SUBSECT. 2. Different Descriptions of Banks in general Use for excluding Waters. 4338. Mounds or banks for excluding rivers or the sea are generally formed of earth, but sometimes also of masonry and even of wood. Embankments of common earth are sufficient for resisting occasional floods: if this earth be loose, the bank will require to be spread out at the base, at the rate of one foot and a half or two feet horizontal for every foot in height; that is to say, a bank of loose earth three feet high will require to be nine feet or twelve feet broad. If the earth to be made use of is a compact clay, or if turf of a solid and compact body can be procured, the slope of the bank may be much steeper, according to its height and the depth of water which may be expected to press against it.

4339. The earthen wall (fig. 665.) is the simplest description of embankment, and is

of turf on the outsides, with

665

frequently erected by temporary occupiers of lands on the general principle of enclosing and subdividing, which is sometimes made a condition of tenure between the landlord and tenant. This wall applies to lands occasionally, but rarely, overflowed or inundated; and is set out in a direction generally parallel to the river or shore. Its base is commenced on the surface, from two to five feet wide, regularly built the grassy sides underneath. The middle of the wall is

centre, so as to finish in a width of one foot or eighteen inches, at five or six feet in height. Collaterally with such walls, and at the distance of three or four feet, a small open drain is formed, as well to collect the surface water of the grounds within, as that which in time of floods will necessarily ooze through a wall of this construction. The water so collected is let through the wall by tubes, or tunnels of boards, with a valve opening outwards on their exterior extremity. When the flow of water from without approaches, it shuts the valve, which remains in this state till the flood subsides, when, the height of the water within being greater than that without, it presses open the valve and escapes. Walls and valves of this kind are common enough in the drier parts of the fenny districts of Lincolnshire and Cambridgeshire.

4340. The earthen mound (fig. 666.) is the most general description of embankment,

666

and, as it is executed at considerable expense, is only undertaken by such as have a permanent interest in the soil. This barrier applies to sea lands overflowed by every spring tide, and to alluvial plains inundated by every flood. It is set out in a direction parallel to the shore, and to the general turns of the river, but not to its minute windings; and it is placed farther from or nearer to the latter, according to the quantity of water in time of floods, the rapidity of the current from the declivity of the bed, the straight course of the stream, and the intended height of the bank. The two sides of such a mound are generally formed in different slopes. That towards the land is always the most abrupt, but can never be secure if more so than 45°; that towards the water varies from 45° to 15°; the power of the bank to resist the weight of the water, as well as to break its force when in motion, being inversely as its steepness. The power of water to lessen the gravity of bodies, or in other words, to loosen the surfaces over which they flow or stand, is also lessened in a ratio somewhat similar.

4341. The formation of the earthen mound consists merely in taking earth from the general surface of the ground to be protected, or from a collateral excavation, distant at least the width of the mound from its base line, and heaping it up in the desired form. The surface is then in general cases covered with turf, well rolled in order to bind it to the loose earth. The earth of such mounds is generally wheeled in barrows; but sometimes it is led in carts placed on a wooden roller instead of wheels, which, with the treading of the horses, serves in some degree to consolidate the bank.

4342. The excavation serves the same purposes as the open drain in the earthen wall; and similarly constructed sluices or valves are introduced on a larger scale. Sometimes, also, the interior water is drawn off by windmills, and thrown over the mound into the river. This is very common in Huntingdonshire, and might be greatly improved on by employing steam engines for entire districts, one of which, of a ten horse power, would do the work of twenty mills, and this in calm weather, when the latter cannot move.

4343. Embankments of this description are the most universal of any, and their sections vary from a scalene triangle of ten feet in base, and three feet in height, as on the Forth near Stirling, and the Thames at Fulham, to a base of 100 feet, and a height of ten feet, as in the great bank of the Ouse, near Wisbeach. The great rivers of Germany and Holland are embanked in this way, when so far from the sea as to be out of the reach of the tide; as the Vistula at Marienwerder, the banks of which, near Dantzic, are above fifteen feet in height; the Oder, the Elbe, &c. All these banks are closely covered in every part with a grassy surface, and sometimes ornamented with rows of trees.

4344. Near the sea, where such banks are washed by every tide when the course of the wind is towards the shore, and by all land floods and spring-tides, grass is only to be found on and near their summits. The rest of the bank is bare, and to preserve it from the action of waves, currents, and the stones, pieces of wood, and other foreign matters which they carry with them, the surface is covered with gravel, reeds, or straw kept down by pieces of wood; faggots, wicker hurdles, nets of straw ropes, straw ropes laid side by side and fastened, or handfuls of straw fixed in the ground with a dibber (Neale's Travels in Germany, &c. chap. i.), or any other contrivance, according to the situation, to prevent the washing away of the bank. It is common to attribute to these coverings the power of breaking the force of the waves; but this power depends, as we have already stated, on the slope of the bank and its smoothness; and the use of the surface covering, and of the constant attention required to remove all obstacles which may be left on it by floods and tides, is to prevent the loosening power of the water from wearing it into holes. For this purpose, a sheet of canvas or straw-netting is as good, whilst it lasts, as a covering of plate iron or stone pavement.

4345. All banks whatever require to be constantly watched in time of floods or spring-tides, in order to remove every object, except sand or mud, which may be left by the water. Such objects, put in motion by the water, in a short time wear out large holes. These holes, presenting abrupt points to the stream, act as obstructions, soon become much larger, and if not immediately filled up, turfed over, and the turfs 667

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b

α

pinned down, or the new turfs ren. dered by some other means not easily softened and raised up by the water, will end in a breach of the bank. A similar effect is produced by a surface formed of unequal degrees of hardness and durability. The banks of this description in Holland, at Cuxhaven, and along the coast of Lincolnshire, are regularly watched throughout the year; the surface protection is repaired whenever it goes out of repair; as is the body of the bank in the summer season.

4346. The mound with puddle wail. fig. 667.) It generally happens that the earth of

such banks is alluvial, and their foundation of the same description; but there are some

cases where the basis is sand, silt, or gravel; or a mud or black earth, as in some parts of Cambridgeshire and Lincolnshire, which does not easily become so compact. Here it is common, before beginning the bank, to bring up from the solid substratum (a) what is called a puddle-ditch, or section of clay in the centre of the highest part of the mound in the direction of its length, and of three or five feet wide, according to the depth of the stratum of silt (6), and the intended height of the bank (c). When the clay of this puddle-ditch is well worked, either by men's feet or clay rammers, the bank will be perfectly impervious to water, and if against a mild stream or shore, need not contain such an accumulation of earth as where the imperviousness of the bank to water depends chiefly on the mass of materials. As already observed, the important point to attend to in this variety of mound is, to found the section, or wall of clay, so deeply as to be in contact with a stratum (a), either by induration, or its argillaceous nature, impervious to water. In the drainage of the Bar Loch in the county of Renfrew, considerable difficulty was experienced in some places in getting to the bottom of the sandy subsoil, so as to bring up the 668

puddle wall from the retentive stratum. Such was the difficulty in some cases, that the puddle could not be carried up perpendicularly, but a puddle wall being raised within the bank, as high as the natural surface, it was joined horizontally to another puddle wall in the body of the bank. (fig. 668.)

4347. Puddling is often found defective, owing to the imperfect working of the materials. Many think that when clay is used, if it be worked into the consistence of dough, it is sufficient; but this is a mistake: it should be slaked and so decomposed by the labour of proper tools and treading, and so completely saturated with water, that the whole mass becomes one uniform and homogeneous body, and almost fluid.

4348. Mounds with reversed slopes. In some cases of embanking rivers, as where they pass through parks, it is desirable to conceal, as much as possible, the appearance of a bank from the protected grounds. Hence the mound is simply reversed, the steepest side being placed next the water. It is proper to observe, that such banks are not so strong, by the difference of the weight of the triangle of water which would rest on the prolonged slope, were it placed next the river, and are more liable to be deranged in surface in proportion to the difference of the slopes, the water acting for a longer period on every part of the slope.

4349. Mound faced with stones. This is the same species of mound, with a slope next the water of forty-five or fifty degrees, paved or causewayed with stones or timber. In Holland this pavement or causeway is often formed of planking or bricks; but in England generally with stones, and the mortar used is either some cement which will set under water, or, what is better, plants of moss firmly rammed between them. The objections to such banks are their expense, and their liability to be undermined invisibly by the admission of the water through crevices, &c. They are, therefore, chiefly used where there is little room, or where it is desirable to narrow and deepen the course of a river. 4350. The bank formed with piles, brushwood, and stones, is occasionally used for protecting moving sands, or directing the course of streams flowing through a sandy shore. A dike or bank for the latter purpose (fig. 669.) has been erected on the river Don in Aberdeen669 shire. It consists of piles or poles, being the thinnings of plantation of Scotch pine and larch, driven six feet into the sand (a a a): the spaces between these piles (bb) are filled in with furze or other spray or small branches; and on the top of them, are wedged in stones to

aaa

keep them down. On the side of this row of piles next the river, stones (c) from 50lbs. to half a ton weight each, are precipitated from a punt, until they form a bank of an angle of nearly 45°. On the outside of this bank and piles, the sand (d) gradually drifts up, and forms a bank, which, being planted with Arúndo arenària and other grasses, gradually becomes covered with verdure. (Highland Soc. Trans. vol. vii. p. 91.)

4351. Mound protected by a wicker hedge. This is a Dutch practice, and, where appearance is no object, has the advantage of not requiring watching. Wicker-work, however, subjected to the strain of waves, will be obviously less durable, than where it lies flat on the ground, and can only decay chemically. This wicker hedge is sometimes a series of hurdles supported by posts and studs; but generally in Britain it is a dead hedge or row of stakes, wattled or wrought with bushes presenting their spray to the sea or river. Besides placing such a hedge before a bank, others are sometimes placed in parallel rows on its surface; the object of which is to entrap sand, shells, and sea weeds, to increase the mass of mound, or to collect shells for the purpose of carrying