714 PRACTICE OF AGRICULTURE. Part III. 



Repertory of Patent Inventions, for January, 1826, and in the JSulletiii des Sciences Agri- 

 coles, for November, 1827. 



4322. Very little has been wntten on the subject of embankments, as a separate branch of 

 art, by British authors. Dugdale's work is entirely historical and topographical. But 

 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, fin 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 Agricidtural 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 arc enabled, by their own v.-cight, 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 loater against the sides of the vessel containing it being as its 

 depth, it folloAvs, 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, con- 

 struction, 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 sulliagc, that the narrower 

 the space is, in which the water is confined, the stronger will be its current, and the less silt will, in ordi- 

 nary 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. 



4328. In Vie 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 construc- 

 tion 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 preventingresistance 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 drabis and floodgates is requisite for the purpose of freeing the em- 

 banked lands from internal waters. 



4331. In designing and setting out the main drain, or discharging channel, on the outside of the embank, 

 ment, 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 con- 

 trary, 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 flood- - 

 gates maybe 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 flood- 

 gate 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 efffected at a great expense, but nevertheless, the improvement being of considerable mag- 

 nitude, 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 



