4 PRACTICE OF AGRICULTURE. Part III. 



breadth of the surface of the latter; and, therefore, that as far as width or extent is con- 

 cerned, it is just as easy to exclude the Atlantic ocean as a pond or a river of a few yards 

 in width. 



4003. Embankments may be considered in regard to their situation, direction, con- 

 struction, and materials. 



4004. The situation of the bank should be such that its base may not be exposed 

 unnecessarily, to the immediate action of the waves, or the current. And, where the 

 quantity of water is limited, as that of land floods in a particular river may be said to 

 be, the more room it has left to spread in, the less height and strength the bank will 

 require ; and the power of the current will be proportionably lessened. It is to be recol- 

 lected, 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. 



4005. 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. 



4006. In the construction or form of the bank there are certain principles to be ob- 

 served. Its height and strength ought ever to be proportioned to the depth and weight 

 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 ofi^'the 

 weight of water. In diflScult cases, the outer surface may form an angle with a per- 

 pendicular line of 45 to 60 degrees, according to the force to be guarded against, and 

 the materials to be employed. 



4007. 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, with- 

 out 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 to be particularly guarded, to prevent its 

 being undermined ; the most mischievous and irreparable disaster of embankments. 

 Hence, when the foundation is not suflficiently firm, piles, timber, and masonry may be 

 required, to insure success. And no man ought to begin a work of this nature, with- 

 out attentively guarding it against every probability of miscarriage. 



4008. A system of drains and floodgates is requisite for the purpose of freeing the em- 

 banked lands from internal waters. 



4009. 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 cuiTcnt of the water into which it opens, is 

 of considerable importance. It ought to be such, that the current of the receiving water 

 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 as given circumstances and a prudent ex- 

 penditure will allow, beneath the floodgate of the embankment ; 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 a still undisturbed situation 

 effectually stops its progress. 



40 1 0. 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 labor and expense. 

 In an obstinate case of this kind on Lord Cawdor's estate, in Pembrokeshire, the dis- 

 charging 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 im- 

 provement being of considerable magnitude, with great profit : and 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, or some defence is necessary. For the 

 floodgate) when loaded, cuts off all communication between the pent up waters and the 



